#4 Read About Improving Soil Fertility
Edited by Len Phillips, updated January 2023
Sections You may go directly to the section by clicking on titles listed here.
Edited by Len Phillips, updated January 2023
Sections You may go directly to the section by clicking on titles listed here.
Click on the green text in each section for more information.
Fertilization of Landscape Trees
Research about trees transplanted from nurseries indicates that there is little benefit to fertilizing at the time of installation. Tree fertilization is not recommended on native soils as well because it is usually unnecessary. Unscreened loam is preferred for better tree growth. Conifers rarely need fertilization at all, since most conifers do well in low-nutrient soils.
Determining the Need for Fertilizer
The best indicator of whether fertilization is necessary is a soil test. Ideally, a soil sample should be taken before trees are installed. In the absence of a soil test, the next best indicator of the need for additional fertilizer on trees is current shoot growth. Depending on the species, if current shoot growth is in excess of 6 inches, then fertilization is not necessary. If shoot growth is between 2 and 6 inches (5 – 15 cm) then fertilizer may be applied and if shoot growth is less than 2 inches (5 cm), then fertilizer applications are appropriate as well as a complete review of the tree to determine if there is anything else that might be wrong with the tree.
Foliage color is another indicator of the need for fertilizer. Again, depending on the species, yellow leaves may indicate the need for fertilizer as these symptoms generally occur on trees that are not taking up enough nutrients or in some instances, the soil is lacking necessary nutrients like iron and manganese.
A final indicator is the history of the location. Trees in locations that are fertilized for gardens or turf on a regular basis rarely need to have supplemental fertilizer applied.
Many soils have low pH levels (5.5 and below) and this may negatively affect trees by reducing the availability of useful nutrients and increase the availability of aluminum, a potentially toxic element. In low pH soils, lime can be applied to raise the pH and it is best done before a tree is installed.
Soils with a pH of over 7.5 can be altered with the use of chemicals, but it is not recommended because it is only a short term fix. The best solution is selecting trees that tolerate a high pH value.
Application Techniques
Many trees are injured each year by human errors during improper fertilization. Mistakes due to calculation errors during mixing, poor application technique, or incorporating the wrong chemical into the tank mix are all too common. While improper mixing and application account for some tree deaths, researchers have also discovered that excess nitrogen and phosphorous (even at the recommended rates of 4 to 6 lbs N/1,000 sq. ft. or 100 sq. m.) have been shown to cause the loss of beneficial mycorrhizal activity and increase the pathogenic activity in the soil.
When to Fertilize
Most trees experience a single flush of growth during spring followed by slower growth throughout the summer and autumn. Because of this single flush of growth, it is desirable to have nutrients available to the tree before this growth occurs. Therefore, the most beneficial time to apply fertilizer is from when the ground is workable in the spring until just before trees start leaf growing a month later. Normally, spring fertilization promotes top growth and autumn fertilization promotes root growth.
If a tree shows a sign that it might indicate a nutrient deficiency, fertilizer can be applied at any time during the growing season. If the fertilizer is applied under hot and dry conditions, it is important to provide water for the tree soon after fertilizer is applied so that salts from the fertilizer do not build up and damage the tree’s root system. One inch of water should be applied every week around the area where fertilizer was applied.
What to Apply
A soil test provides the best indicator of elements that may need to be added to the soil to prevent nutrient problems. Unless a tree is deficient in some other element, increased nitrogen (N), more than any other plant nutrient, provides the most pronounced effects on the growth. Just because an increase in N produces a more visible increase in growth, it does not mean that other elements are not required.
High rates of phosphorous (P) should not be applied unless a need is indicated by the soil test. High rates of P can negatively affect the environment, especially lakes and streams. Never use a fertilizer that includes any kind of herbicide around a tree. These broadleaf fertilizers may be beneficial to plants, but the herbicide can damage these same broadleaf trees.
Application Methods and Rates
Trees typically go through 3 stages of nitrogen need.
1. During the newly planted phase, quick release N levels should not exceed 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.) per year or a higher rate of a slow release fertilizer, up to 0.2 lb N/100 sq. ft. (90 g. N/10 sq. m.) per year, can be used. Slow releasing and inorganic fertilizers can be incorporated into the backfill soil. Quick release fertilizers should be broadcast after tree installation and then watered in. Do not mix quick release forms with the soil used to backfill the installation hole, because direct contact with fertilizer will burn the roots.
2. On young landscape trees and shrubs where rapid growth is desirable, use 0.2 to 0.4 lb N/100 sq. ft. (90 g. N/10 sq. m.) per year. For trees in lawn areas, do not exceed 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.) per application unless a slow release or inorganic fertilizer is used. Higher rates will burn the grass. Recent research indicates that fertilizer at this stage has only a slight enhancement of tree growth.
3. As trees and shrubs mature, and the growth rate naturally slows down, the need for N drops to a level to maintain landscape plants in a healthy condition without excessive vegetative growth.
Too much nitrogen fertilizer will push leaf development at a rate faster than the roots can support. Too much fertilizer will also cause a fertilizer burn. This occurs because the high concentration of fertilizer draws water out of the root and into the soil, in turn causing a drought condition to occur in the tree. Flooding the root zone with water should reverse the problem, provided the soil is well drained.
Surface Fertilizer Application
Plants respond best to surface applications of fertilizer that are broadcast over the area where the tree roots lie. A late autumn or early winter application will provide the tree with the maximum value from the nutrients. Dry or granular fertilizers can be applied by hand or with the use of a mechanical spreader. Trees should always be watered around the area of fertilizer application soon after the fertilizer has been applied. This helps to ensure that the fertilizer will move down to the trees’ root system before it can be taken up by weeds or grass. A good rain (1 – 2")(2 – 5 cm) will also be sufficient to move fertilizer to the trees root zone.
Drill-hole Fertilizer Application
For established trees requiring phosphorus or potassium, or to apply a higher rate of fertilizer than 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.), fertilizer can be applied using the drill-hole method. This method is advantageous for supplying phosphorus and potassium to trees because these nutrients are relatively immobile in soils. Drilling holes will reduce soil compaction and increase aeration. However, the drill hole method is extremely time consuming. Generally, the drill-hole method is only used by professional landscapers for high value trees and trees under extreme nutrient stress.
The drill-hole application method involves digging holes 2 feet (0.6 m.) apart with a soil auger in a grid pattern with the tree at the center of this pattern. Holes should begin 3 feet (1 m.) from the trunk of the tree and be 1½ to 2 inches (30 – 50 cm.) in diameter and 1 – 1½ feet (0.3 – 0.5 m.) deep. The holes should be drilled in a series of parallel lines under the spread of the tree and extending 2 feet (0.6 m.) beyond the drip line. For columnar trees, holes should be drilled 4 to 6 feet (1.2 – 1.8 m.) beyond the drip line.
To calculate the amount of fertilizer to place into each hole, use the following formula: (100/analysis of N in fertilizer) × 0.12 = amount of fertilizer to add to each hole in teaspoons. For example, if you are using a fertilizer with an analysis of 18-8-8, then use (100 /18) × 0.12 = 0.66 or 2/3 teaspoons of fertilizer per hole. After the holes are dug, place the recommended quantity of fertilizer in each hole, water the fertilizer in, and refill the holes.
Hydraulic Fertilizer Application
Hydraulic injection of liquid fertilizers into the root zone of the tree is an acceptable way to provide nutrients and may be offered by some specialty tree care companies. The use of specialized equipment and fertilizers increases cost. However, when a large number of trees need to be fertilized this system may become an economical alternative. Injections are applied in a grid pattern similar to the drill-hole method except that injection sites should be 3 feet (1 meter) from each other and should extend 15 feet (4.6 m.) from the base of the tree as with the drill-hole method. Hydraulic injection allows nutrients, including immobile elements, to be available to the tree more rapidly than any other fertilizer application alternative.
Foliar Fertilizer Application
To rapidly correct certain micro-nutrient problems, iron, zinc, and manganese, foliar fertilization supplies the needed nutrients directly to the leaf, where they are needed. Foliar applications, usually applied to landscape trees with a hand held sprayer, are effective in correcting specific nutrient deficiencies for a short period of time. Soil pH adjustment and additional soil application of these nutrients are required to correct the problem for the long-term. Pesticides can also be applied as a foliar spray. However, foliar sprays are difficult to apply to large trees and the materials will sometimes leave a whitish film or spots on the leaves. Spray drift is also a major concern.
Fertilizer Injection Application
Another rapid way to correct micro-nutrient problems is by injecting the necessary nutrients directly into the trunk of the tree. The micro-injection technique requires a good understanding of how a tree system absorbs nutrients, compartmentalizes wounds, and recovers from the small injury created by the process. To follow the basic guidelines of micro-injection, the arborist/technician must know proper placement, size, and depth of the injection hole, and the acceptable conditions under which proper injections should take place. When fertilizer is injected into the sap stream of the tree, the material moves quickly throughout the entire vascular system. The individual components go directly to where they are needed for optimum benefit to the tree. With other fertilization methods, the tree is dependent on the technician to place the material near all the fine absorbing roots.
pH Adjustments
In cases where the soil pH is above the optimum range for the growth of a particular plant species, interveinal chlorosis, or yellowing between veins, may occur on their foliage. This chlorosis is an indication of poor iron availability in the soil. The soil contains enough iron, but the plant is not able to take up and use the iron efficiently. The solution is to decrease the pH of the soil and apply iron chelate to the leaves or the soil. Foliar applications of iron chelate needs to be made several times during the growing season. Generally it is better to match the tree's preferred pH range to the soil than to try to change the soil.
Summary
It is not common that trees suffer from soil nutrient deficiencies. More often, the cause of the suffering is from inadequate water, poor or damaged root systems, or a high soil pH. The tree may be perfectly healthy for the site it is growing in. However, if a newly installed tree is in poor soil or if there is a need for more rapid growth, fertilization can be beneficial. Water is still the overriding amendment that determines plant health, even for established, mature trees.
As an old nurseryman once told me, “The three best fertilizers for a tree are: water; water; and more water. Water once when installing the tree; water again the next day; and water again once every week for the remainder of the growing season.” After that, the tree should do well on its own.
Fertilization of Landscape Trees
Research about trees transplanted from nurseries indicates that there is little benefit to fertilizing at the time of installation. Tree fertilization is not recommended on native soils as well because it is usually unnecessary. Unscreened loam is preferred for better tree growth. Conifers rarely need fertilization at all, since most conifers do well in low-nutrient soils.
Determining the Need for Fertilizer
The best indicator of whether fertilization is necessary is a soil test. Ideally, a soil sample should be taken before trees are installed. In the absence of a soil test, the next best indicator of the need for additional fertilizer on trees is current shoot growth. Depending on the species, if current shoot growth is in excess of 6 inches, then fertilization is not necessary. If shoot growth is between 2 and 6 inches (5 – 15 cm) then fertilizer may be applied and if shoot growth is less than 2 inches (5 cm), then fertilizer applications are appropriate as well as a complete review of the tree to determine if there is anything else that might be wrong with the tree.
Foliage color is another indicator of the need for fertilizer. Again, depending on the species, yellow leaves may indicate the need for fertilizer as these symptoms generally occur on trees that are not taking up enough nutrients or in some instances, the soil is lacking necessary nutrients like iron and manganese.
A final indicator is the history of the location. Trees in locations that are fertilized for gardens or turf on a regular basis rarely need to have supplemental fertilizer applied.
Many soils have low pH levels (5.5 and below) and this may negatively affect trees by reducing the availability of useful nutrients and increase the availability of aluminum, a potentially toxic element. In low pH soils, lime can be applied to raise the pH and it is best done before a tree is installed.
Soils with a pH of over 7.5 can be altered with the use of chemicals, but it is not recommended because it is only a short term fix. The best solution is selecting trees that tolerate a high pH value.
Application Techniques
Many trees are injured each year by human errors during improper fertilization. Mistakes due to calculation errors during mixing, poor application technique, or incorporating the wrong chemical into the tank mix are all too common. While improper mixing and application account for some tree deaths, researchers have also discovered that excess nitrogen and phosphorous (even at the recommended rates of 4 to 6 lbs N/1,000 sq. ft. or 100 sq. m.) have been shown to cause the loss of beneficial mycorrhizal activity and increase the pathogenic activity in the soil.
When to Fertilize
Most trees experience a single flush of growth during spring followed by slower growth throughout the summer and autumn. Because of this single flush of growth, it is desirable to have nutrients available to the tree before this growth occurs. Therefore, the most beneficial time to apply fertilizer is from when the ground is workable in the spring until just before trees start leaf growing a month later. Normally, spring fertilization promotes top growth and autumn fertilization promotes root growth.
If a tree shows a sign that it might indicate a nutrient deficiency, fertilizer can be applied at any time during the growing season. If the fertilizer is applied under hot and dry conditions, it is important to provide water for the tree soon after fertilizer is applied so that salts from the fertilizer do not build up and damage the tree’s root system. One inch of water should be applied every week around the area where fertilizer was applied.
What to Apply
A soil test provides the best indicator of elements that may need to be added to the soil to prevent nutrient problems. Unless a tree is deficient in some other element, increased nitrogen (N), more than any other plant nutrient, provides the most pronounced effects on the growth. Just because an increase in N produces a more visible increase in growth, it does not mean that other elements are not required.
High rates of phosphorous (P) should not be applied unless a need is indicated by the soil test. High rates of P can negatively affect the environment, especially lakes and streams. Never use a fertilizer that includes any kind of herbicide around a tree. These broadleaf fertilizers may be beneficial to plants, but the herbicide can damage these same broadleaf trees.
Application Methods and Rates
Trees typically go through 3 stages of nitrogen need.
1. During the newly planted phase, quick release N levels should not exceed 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.) per year or a higher rate of a slow release fertilizer, up to 0.2 lb N/100 sq. ft. (90 g. N/10 sq. m.) per year, can be used. Slow releasing and inorganic fertilizers can be incorporated into the backfill soil. Quick release fertilizers should be broadcast after tree installation and then watered in. Do not mix quick release forms with the soil used to backfill the installation hole, because direct contact with fertilizer will burn the roots.
2. On young landscape trees and shrubs where rapid growth is desirable, use 0.2 to 0.4 lb N/100 sq. ft. (90 g. N/10 sq. m.) per year. For trees in lawn areas, do not exceed 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.) per application unless a slow release or inorganic fertilizer is used. Higher rates will burn the grass. Recent research indicates that fertilizer at this stage has only a slight enhancement of tree growth.
3. As trees and shrubs mature, and the growth rate naturally slows down, the need for N drops to a level to maintain landscape plants in a healthy condition without excessive vegetative growth.
Too much nitrogen fertilizer will push leaf development at a rate faster than the roots can support. Too much fertilizer will also cause a fertilizer burn. This occurs because the high concentration of fertilizer draws water out of the root and into the soil, in turn causing a drought condition to occur in the tree. Flooding the root zone with water should reverse the problem, provided the soil is well drained.
Surface Fertilizer Application
Plants respond best to surface applications of fertilizer that are broadcast over the area where the tree roots lie. A late autumn or early winter application will provide the tree with the maximum value from the nutrients. Dry or granular fertilizers can be applied by hand or with the use of a mechanical spreader. Trees should always be watered around the area of fertilizer application soon after the fertilizer has been applied. This helps to ensure that the fertilizer will move down to the trees’ root system before it can be taken up by weeds or grass. A good rain (1 – 2")(2 – 5 cm) will also be sufficient to move fertilizer to the trees root zone.
Drill-hole Fertilizer Application
For established trees requiring phosphorus or potassium, or to apply a higher rate of fertilizer than 0.1 lb N/100 sq. ft. (45 g. N/10 sq. m.), fertilizer can be applied using the drill-hole method. This method is advantageous for supplying phosphorus and potassium to trees because these nutrients are relatively immobile in soils. Drilling holes will reduce soil compaction and increase aeration. However, the drill hole method is extremely time consuming. Generally, the drill-hole method is only used by professional landscapers for high value trees and trees under extreme nutrient stress.
The drill-hole application method involves digging holes 2 feet (0.6 m.) apart with a soil auger in a grid pattern with the tree at the center of this pattern. Holes should begin 3 feet (1 m.) from the trunk of the tree and be 1½ to 2 inches (30 – 50 cm.) in diameter and 1 – 1½ feet (0.3 – 0.5 m.) deep. The holes should be drilled in a series of parallel lines under the spread of the tree and extending 2 feet (0.6 m.) beyond the drip line. For columnar trees, holes should be drilled 4 to 6 feet (1.2 – 1.8 m.) beyond the drip line.
To calculate the amount of fertilizer to place into each hole, use the following formula: (100/analysis of N in fertilizer) × 0.12 = amount of fertilizer to add to each hole in teaspoons. For example, if you are using a fertilizer with an analysis of 18-8-8, then use (100 /18) × 0.12 = 0.66 or 2/3 teaspoons of fertilizer per hole. After the holes are dug, place the recommended quantity of fertilizer in each hole, water the fertilizer in, and refill the holes.
Hydraulic Fertilizer Application
Hydraulic injection of liquid fertilizers into the root zone of the tree is an acceptable way to provide nutrients and may be offered by some specialty tree care companies. The use of specialized equipment and fertilizers increases cost. However, when a large number of trees need to be fertilized this system may become an economical alternative. Injections are applied in a grid pattern similar to the drill-hole method except that injection sites should be 3 feet (1 meter) from each other and should extend 15 feet (4.6 m.) from the base of the tree as with the drill-hole method. Hydraulic injection allows nutrients, including immobile elements, to be available to the tree more rapidly than any other fertilizer application alternative.
Foliar Fertilizer Application
To rapidly correct certain micro-nutrient problems, iron, zinc, and manganese, foliar fertilization supplies the needed nutrients directly to the leaf, where they are needed. Foliar applications, usually applied to landscape trees with a hand held sprayer, are effective in correcting specific nutrient deficiencies for a short period of time. Soil pH adjustment and additional soil application of these nutrients are required to correct the problem for the long-term. Pesticides can also be applied as a foliar spray. However, foliar sprays are difficult to apply to large trees and the materials will sometimes leave a whitish film or spots on the leaves. Spray drift is also a major concern.
Fertilizer Injection Application
Another rapid way to correct micro-nutrient problems is by injecting the necessary nutrients directly into the trunk of the tree. The micro-injection technique requires a good understanding of how a tree system absorbs nutrients, compartmentalizes wounds, and recovers from the small injury created by the process. To follow the basic guidelines of micro-injection, the arborist/technician must know proper placement, size, and depth of the injection hole, and the acceptable conditions under which proper injections should take place. When fertilizer is injected into the sap stream of the tree, the material moves quickly throughout the entire vascular system. The individual components go directly to where they are needed for optimum benefit to the tree. With other fertilization methods, the tree is dependent on the technician to place the material near all the fine absorbing roots.
pH Adjustments
In cases where the soil pH is above the optimum range for the growth of a particular plant species, interveinal chlorosis, or yellowing between veins, may occur on their foliage. This chlorosis is an indication of poor iron availability in the soil. The soil contains enough iron, but the plant is not able to take up and use the iron efficiently. The solution is to decrease the pH of the soil and apply iron chelate to the leaves or the soil. Foliar applications of iron chelate needs to be made several times during the growing season. Generally it is better to match the tree's preferred pH range to the soil than to try to change the soil.
Summary
It is not common that trees suffer from soil nutrient deficiencies. More often, the cause of the suffering is from inadequate water, poor or damaged root systems, or a high soil pH. The tree may be perfectly healthy for the site it is growing in. However, if a newly installed tree is in poor soil or if there is a need for more rapid growth, fertilization can be beneficial. Water is still the overriding amendment that determines plant health, even for established, mature trees.
As an old nurseryman once told me, “The three best fertilizers for a tree are: water; water; and more water. Water once when installing the tree; water again the next day; and water again once every week for the remainder of the growing season.” After that, the tree should do well on its own.
Fertilizer Components
Fertilizer consists of elements or nutrients that are easily released into the soil for a plant to absorb.
Macronutrients
There are three nutrients known as macro-nutrients that are the primary ingredients in most fertilizers. They are nitrogen (N), phosphorus (P), and potassium (K). While they may be only three of the 17 elements known to be essential for tree growth, a fertilizer will be considered to be complete when it is comprised of varying percentages of these three elements.
Nitrogen
Nitrogen is the main element to consider in choosing a fertilizer. Nitrogen encourages above ground vegetative growth. Nitrogen is the fundamental element in amino acids and proteins, the building blocks of life, and is a major component of DNA and RNA. Deficiencies in nitrogen can be noted in the yellowing of mature leaves and stunted growth. Nitrogen is often in short supply because watering and rainfall flush it from the soil.
Nitrogen is the most volatile and transient of all the elements used by a tree. It is estimated that of all the nitrogen fertilizer that is put in the ground, the tree uses only .001%. The rest is sucked up by other organisms, volatilized, leached away into ground water, or is simply turned back into nitrogen gas by soil organisms.
The growing plant needs a continuous supply of nitrogen. Air is the source of about 78% of nitrogen by volume. Other sources include soluble sources of nitrogen in the soil. On many fertilizer bags are the letters W.I.N. (Water Insoluble Nitrogen). The higher the percentage of W.I.N., the safer and longer lasting the nitrogen will be and nitrogen will be available at a slow and steady rate.
Phosphorus
Phosphorus is important for seedling development, cell building, disease resistance, and root growth. Phosphorous is also used in the transfer of energy as Adenosine TriPhosphate (ATP) and is the adhesive component of DNA and RNA. The symptoms from a lack of phosphorus appear in the lower leaves and show a lack of chlorophyll, blotches of deep green, or a reddish color in the leaves. Unfortunately, cold temperature, high light intensity, insect damage, and drought can also induce foliar reddening. Deficient trees have weak roots, delayed maturity, and low flower and fruiting. Adding phosphate to trees increases color as well as vigor and simulates growth. Over fertilizing with phosphorus results in leaf chlorosis and is detrimental to mycorrhizal health. Excess phosphate will also find its way into waterways and induce algal blooms and eutrophication. To control excess phosphorus, add and maintain organic soil and mulch on the soil surface. This provides a slow release of phosphorus and other needed macro and micro-nutrients over time.
Phosphorus is the plant nutrient in the soil that is in the greatest demand because it is not readily recycled by microorganisms. Phosphorus is usually made available to trees through the breakdown of organic matter and soil minerals, by fungi in the soil. This breakdown lets phosphorus enter plants as phosphate.
The plant uses only about 10% to 20% of the phosphorus applied by fertilizer. It does not move within the soil except by cultivation. Research has indicated that phosphorus is also affected by the moisture supply. Good watering practices and cool weather help maximize the available phosphorus. Urban sites, where there is little organic material, will usually be deficient in available phosphorous, even though it is a major component in forest soils.
Potassium
Potassium, also called potash, assists plants in forming starches and proteins and helps trees resist disease. Potassium is usually adequate in the soil. Since it is unavailable to plants in mineral form, sandy soils are particularly susceptible to leaching of potassium salts. Trees use potassium in large amounts in the production of sugar, respiration, transpiration, and synthesis of proteins. It is released slowly from the soil and becomes a deficiency to the tree during peak growth periods. Deficiencies result in slow growth and scorched leaves, particularly at the tip and along the margins. By adding potassium to the tree, you also increase insect and disease resistance.
The total potassium content of U.S. soils generally increases from east to west and from south to north in the eastern half of the U.S. Many trees use as much potassium as they do nitrogen, which is three to four times the amount of phosphorus used. Because potassium may be leached from the soil, annual applications should be made in sufficient quantities to supply the plant's needs.
Secondary Nutrients
Many fertilizers contain secondary nutrients or micro-elements Many micro-elements are used by trees in similar quantities to macro-elements, but are generally found in more available forms.
Calcium is common in most soils and is ranked third behind nitrogen and potassium in use by plants. It is used mainly in cell walls and interactions with potassium and magnesium.
Magnesium is abundant in most soils. Magnesium is a key ingredient in chlorophyll, is active in enzymes, interacts with phosphorus for translocation from cell to cell, and is most abundant at the meristem. When magnesium is lacking, leaves turn light green with streaks or bands and the leaf margins appear up-turned. Tip necrosis is also a sign while lower branches may be deep green. In the Southeast and in warmer coastal areas, palm trees are particularly prone to deficiencies.
Lime is the principal source of calcium and magnesium in most areas. Lime can be added to the soil in several forms: agricultural lime, dolomite, marl (lime rich mud), and others. In areas where the soil is neutral to alkaline, there is normally enough calcium and magnesium naturally available in the soil for the plant's needs.
Sulfur is just as important as nitrogen for the making of new protoplasm for plant cells. Sulfur is found in organic matter and the atmosphere in the form of sulfur dioxide. It is vital in many amino acids and proteins used in plant growth, and it is a vital portion of enzymes. Sulfur chlorosis appears interveinally with stunted new growth. Excessive sulfur causes pH imbalances that can reduce the availability of other micro-elements
Iron is the most common cause of chlorosis in trees. Iron is needed for chlorophyll synthesis, enzyme activity, and other energy transport reactions. Iron is fixed in plant tissues and will not move. Some species like Pin Oak require more iron than others and needles of conifers lacking in iron turn yellow-green. Iron must be administered before new leaves appear in the spring to be effective.
Micro-nutrients
The amounts of the micro-nutrients are necessary in small doses for trees. They are nevertheless essential to plants. Specific micro-nutrients may need to be added to the soil when deficiency symptoms occur. Many commercial fertilizers contain micro-nutrients as part of the formulation. However, micro-nutrients are seldom in short supply in most soils. The diagnosis of micro-nutrient deficiency is tricky, because many environmental (e.g., drought) and structural (e.g., girdling root) problems can also produce chlorotic leaves. Micro-nutrient deficiencies on urban trees are often due to a high pH (7.8-8.2 on soils with significant lime content from the leaching of concrete sidewalks) that makes these elements not available to the plant.
Manganese is a micro-element that falls into a category similar to iron. It is needed for chlorophyll and activates certain enzyme reactions. Manganese interrelates with iron and is also immobile. Manganese deficiency often appears whitish in color on new growth. Since both iron and manganese are closely connected, a misdiagnosis can result. A mildly chlorotic plant as a result of manganese deficiency may become severely chlorotic if iron is used to correct the problem. Therefore it is necessary to treat with both elements in this situation. Plant tissue analysis can determine which element is missing, but results are often unreliable. Using both iron and manganese in a 3:1 ratio is justified when treating these problems.
Zinc is found in most soils but is commonly needed along the U.S. Gulf Coast and in sandy soils. Some plants, particularly pecans and conifers, benefit from high levels of zinc. Zinc serves as a catalyst along with copper and manganese and is essential for photosynthesis. Together with copper, zinc aids in the reduction of nitrogen. Zinc chlorosis appears uniform, sometimes with necrotic spots and small leaves that are narrow and pointed. Terminal meristems produce rosettes of leaves that die back. Fruit is small and highly colored.
Copper is found in enzyme reactions. Although this element is almost never found to be a deficiency, it has been demonstrated that the addition of small amounts of copper affects a tree's metabolism. This results in greater tree vitality and vigor.
Molybdenum is important for nitrate utilization by plants.
Boron and Chlorine are only needed in extremely small amounts. Boron is applied in calcium usage and assists with sugar movement, while chlorine is used to regulate osmotic pressures and ionic chemical exchange.
Sodium is needed by certain plants for maintaining osmotic pressure and photosynthesis,
Cobalt is needed by microorganisms within certain plants for nitrogen fixation, but is not used in the plant system itself.
Fertilizer consists of elements or nutrients that are easily released into the soil for a plant to absorb.
Macronutrients
There are three nutrients known as macro-nutrients that are the primary ingredients in most fertilizers. They are nitrogen (N), phosphorus (P), and potassium (K). While they may be only three of the 17 elements known to be essential for tree growth, a fertilizer will be considered to be complete when it is comprised of varying percentages of these three elements.
Nitrogen
Nitrogen is the main element to consider in choosing a fertilizer. Nitrogen encourages above ground vegetative growth. Nitrogen is the fundamental element in amino acids and proteins, the building blocks of life, and is a major component of DNA and RNA. Deficiencies in nitrogen can be noted in the yellowing of mature leaves and stunted growth. Nitrogen is often in short supply because watering and rainfall flush it from the soil.
Nitrogen is the most volatile and transient of all the elements used by a tree. It is estimated that of all the nitrogen fertilizer that is put in the ground, the tree uses only .001%. The rest is sucked up by other organisms, volatilized, leached away into ground water, or is simply turned back into nitrogen gas by soil organisms.
The growing plant needs a continuous supply of nitrogen. Air is the source of about 78% of nitrogen by volume. Other sources include soluble sources of nitrogen in the soil. On many fertilizer bags are the letters W.I.N. (Water Insoluble Nitrogen). The higher the percentage of W.I.N., the safer and longer lasting the nitrogen will be and nitrogen will be available at a slow and steady rate.
Phosphorus
Phosphorus is important for seedling development, cell building, disease resistance, and root growth. Phosphorous is also used in the transfer of energy as Adenosine TriPhosphate (ATP) and is the adhesive component of DNA and RNA. The symptoms from a lack of phosphorus appear in the lower leaves and show a lack of chlorophyll, blotches of deep green, or a reddish color in the leaves. Unfortunately, cold temperature, high light intensity, insect damage, and drought can also induce foliar reddening. Deficient trees have weak roots, delayed maturity, and low flower and fruiting. Adding phosphate to trees increases color as well as vigor and simulates growth. Over fertilizing with phosphorus results in leaf chlorosis and is detrimental to mycorrhizal health. Excess phosphate will also find its way into waterways and induce algal blooms and eutrophication. To control excess phosphorus, add and maintain organic soil and mulch on the soil surface. This provides a slow release of phosphorus and other needed macro and micro-nutrients over time.
Phosphorus is the plant nutrient in the soil that is in the greatest demand because it is not readily recycled by microorganisms. Phosphorus is usually made available to trees through the breakdown of organic matter and soil minerals, by fungi in the soil. This breakdown lets phosphorus enter plants as phosphate.
The plant uses only about 10% to 20% of the phosphorus applied by fertilizer. It does not move within the soil except by cultivation. Research has indicated that phosphorus is also affected by the moisture supply. Good watering practices and cool weather help maximize the available phosphorus. Urban sites, where there is little organic material, will usually be deficient in available phosphorous, even though it is a major component in forest soils.
Potassium
Potassium, also called potash, assists plants in forming starches and proteins and helps trees resist disease. Potassium is usually adequate in the soil. Since it is unavailable to plants in mineral form, sandy soils are particularly susceptible to leaching of potassium salts. Trees use potassium in large amounts in the production of sugar, respiration, transpiration, and synthesis of proteins. It is released slowly from the soil and becomes a deficiency to the tree during peak growth periods. Deficiencies result in slow growth and scorched leaves, particularly at the tip and along the margins. By adding potassium to the tree, you also increase insect and disease resistance.
The total potassium content of U.S. soils generally increases from east to west and from south to north in the eastern half of the U.S. Many trees use as much potassium as they do nitrogen, which is three to four times the amount of phosphorus used. Because potassium may be leached from the soil, annual applications should be made in sufficient quantities to supply the plant's needs.
Secondary Nutrients
Many fertilizers contain secondary nutrients or micro-elements Many micro-elements are used by trees in similar quantities to macro-elements, but are generally found in more available forms.
Calcium is common in most soils and is ranked third behind nitrogen and potassium in use by plants. It is used mainly in cell walls and interactions with potassium and magnesium.
Magnesium is abundant in most soils. Magnesium is a key ingredient in chlorophyll, is active in enzymes, interacts with phosphorus for translocation from cell to cell, and is most abundant at the meristem. When magnesium is lacking, leaves turn light green with streaks or bands and the leaf margins appear up-turned. Tip necrosis is also a sign while lower branches may be deep green. In the Southeast and in warmer coastal areas, palm trees are particularly prone to deficiencies.
Lime is the principal source of calcium and magnesium in most areas. Lime can be added to the soil in several forms: agricultural lime, dolomite, marl (lime rich mud), and others. In areas where the soil is neutral to alkaline, there is normally enough calcium and magnesium naturally available in the soil for the plant's needs.
Sulfur is just as important as nitrogen for the making of new protoplasm for plant cells. Sulfur is found in organic matter and the atmosphere in the form of sulfur dioxide. It is vital in many amino acids and proteins used in plant growth, and it is a vital portion of enzymes. Sulfur chlorosis appears interveinally with stunted new growth. Excessive sulfur causes pH imbalances that can reduce the availability of other micro-elements
Iron is the most common cause of chlorosis in trees. Iron is needed for chlorophyll synthesis, enzyme activity, and other energy transport reactions. Iron is fixed in plant tissues and will not move. Some species like Pin Oak require more iron than others and needles of conifers lacking in iron turn yellow-green. Iron must be administered before new leaves appear in the spring to be effective.
Micro-nutrients
The amounts of the micro-nutrients are necessary in small doses for trees. They are nevertheless essential to plants. Specific micro-nutrients may need to be added to the soil when deficiency symptoms occur. Many commercial fertilizers contain micro-nutrients as part of the formulation. However, micro-nutrients are seldom in short supply in most soils. The diagnosis of micro-nutrient deficiency is tricky, because many environmental (e.g., drought) and structural (e.g., girdling root) problems can also produce chlorotic leaves. Micro-nutrient deficiencies on urban trees are often due to a high pH (7.8-8.2 on soils with significant lime content from the leaching of concrete sidewalks) that makes these elements not available to the plant.
Manganese is a micro-element that falls into a category similar to iron. It is needed for chlorophyll and activates certain enzyme reactions. Manganese interrelates with iron and is also immobile. Manganese deficiency often appears whitish in color on new growth. Since both iron and manganese are closely connected, a misdiagnosis can result. A mildly chlorotic plant as a result of manganese deficiency may become severely chlorotic if iron is used to correct the problem. Therefore it is necessary to treat with both elements in this situation. Plant tissue analysis can determine which element is missing, but results are often unreliable. Using both iron and manganese in a 3:1 ratio is justified when treating these problems.
Zinc is found in most soils but is commonly needed along the U.S. Gulf Coast and in sandy soils. Some plants, particularly pecans and conifers, benefit from high levels of zinc. Zinc serves as a catalyst along with copper and manganese and is essential for photosynthesis. Together with copper, zinc aids in the reduction of nitrogen. Zinc chlorosis appears uniform, sometimes with necrotic spots and small leaves that are narrow and pointed. Terminal meristems produce rosettes of leaves that die back. Fruit is small and highly colored.
Copper is found in enzyme reactions. Although this element is almost never found to be a deficiency, it has been demonstrated that the addition of small amounts of copper affects a tree's metabolism. This results in greater tree vitality and vigor.
Molybdenum is important for nitrate utilization by plants.
Boron and Chlorine are only needed in extremely small amounts. Boron is applied in calcium usage and assists with sugar movement, while chlorine is used to regulate osmotic pressures and ionic chemical exchange.
Sodium is needed by certain plants for maintaining osmotic pressure and photosynthesis,
Cobalt is needed by microorganisms within certain plants for nitrogen fixation, but is not used in the plant system itself.
Fertilizer Types
Fertilizer Label
The labels on containers of fertilizer must carry the specific analysis, which is the weight percentage of the three major nutrients in the fertilizer mix:
Total N means the total amount of ammoniacal N, urea N, water insoluble N, and other recognized and determinable forms of N. The N breakdown statement is only required when slow release or organic N properties are claimed or guaranteed.
When reading the label, a 20-10-10 analysis for example, would contain 20% total N, 10% P2O5, and 10% K2O. Therefore, a fifty-pound bag of fertilizer with this analysis would contain ten pounds of total N, five pounds of P2O5, and five pounds of K2O, or a total of twenty pounds of plant food. The other 60% would consist of inert material or minor nutrients. Always read the ingredients and follow all label directions prior to applying fertilizer.
There are many formulations, but the listings are always in the same order, with N first, followed by P2O5, and K2O. The specific fertilizer ratio needed will depend on the soil nutrient level. One general rule can be established: the percentage of N in the formula usually dictates the amount of fertilizer to be applied.
When other plant nutrients in addition to N, P, or K are guaranteed, they must be listed in columnar form immediately below the primary nutrient guarantees and always in the following order with minimum percentages listed: Calcium (Ca); Magnesium (Mg); Sulfur (S); Boron (B); Chlorine (Cl); Cobalt (Co); Copper (Cu); Iron (Fe); Manganese (Mn); Molybdenum (Mo); Sodium (Na); and Zinc (Zn).
Fertilizer Types
There are three types of fertilizers: organic, inorganic, and slow release fertilizer.
1. Organic Fertilizer
The significant difference between natural organics and chemical inorganics is that organisms in the soil must release N into natural organics before it can become food for the tree. Therefore, since they are not soluble in water, they are less likely to be lost through leaching, and they are slow-releasing and non-burning. Natural
organics are usually low in N.
Organic fertilizers are derived from nature, such as manure, sludge, etc., and are marketable in dry form only. There are also synthetic organic fertilizers such as urea formaldehyde and isobutylidene diurea. All of these materials act more slowly than other fertilizers, thus reducing the danger of over-fertilization. However, those
that have a low percentage of N are bulkier and heavier to handle because they must be applied in much
greater quantities. These materials release the fertilizing elements somewhat unpredictably when the soil is
warm.
Bone meal decomposes slowly and thus releases P2O5 slowly. It is a well-known additive at the bottom of the
hole for bulb planting. Another advantage of bone meal is that it helps neutralize the acidity of peat based
potting mixes.
Cottonseed meal is a by-product of cotton manufacturing. It is somewhat acidic in reaction as a fertilizer.
Formulas vary slightly, but are generally 7-3-2. Cottonseed meal is available in warm soils and there is little
danger of over-fertilizing. It is used with acid loving plants.
Fish emulsion is a fertilizer made from fish byproducts. A major disadvantage is the intense odor; however, the
smell will dissipate in a day or two. Fish emulsion is high in N and is a source of several trace elements. It is
excellent for use in the late winter to boost the early growth spurt. It is possible to 'burn' plants if too strong a
solution is applied.
Seaweed is a source of trace metals and growth hormones. Its greatest disadvantage is the high cost. This
form of fertilizer is usually used for houseplants, but experimentation continues for tree and garden use.
Manure comes in several types including horse, cow, pig, chicken, and sheep products. Fresh manures have
the highest concentration of nutrients, but when they are aged or composted, the nutrient content is reduced.
Fresh manure should not be used where it will come into contact with tender roots. Composted forms are
more commonly used to reduce burning the plant roots. Manures are useful for increasing the organic content
of the soil, improving soil structure, and increasing bacterial activity. Manure should be spread evenly and
dug, rototilled, or plowed under.
Sewage sludge or biosolid is a recycled product from municipal sewage treatment plants. Activated sludge
has higher concentrations of nutrients (approximately 6-3-5) compared to composted sludge. It is usually sold
in a dry, granular form for general-purpose use and as a long-lasting, non-burning fertilizer. Composted sludge
is mainly used as a soil additive and has a lower nutrient content (approx. 2-3-0).
2. Inorganic Fertilizer
The blended inorganic fertilizers readily break down in the soil and quickly bring nutrients to the plants. These
fertilizers are soluble in water. They are often termed "hot fertilizers" because they contain salts and various
mineral compounds that can burn tree roots if not handled properly. The chief advantage is that they contain a
high ratio of N, P2O5, and K2O. While inorganic fertilizer supplies nutrients to the soil, it does not feed soil
microorganisms. It is the soil microorganisms that are essential for long-term release of nutrients stored in
organic matter. Inorganic fertilizers are generally used for agricultural crops and turfgrass.
Inorganic fertilizers are chemical or mineral products available in dry or liquid form. The N becomes available
from bacterial action over a longer period of time and thus extends its fertilizing action gradually. Slow-
release pellets, packets, and sticks are available for tree fertilization. These pellets are an acceptable source
of nutrients. However, compared to surface application, they do not provide good lateral movement of
nutrients, are somewhat expensive, and have to be reapplied periodically.
Soluble inorganics include urea, ammonium sulfate, ammonium nitrate, potassium nitrate, and sodium nitrate.
They are inexpensive and have a very high level of N.
3. Slow-Release Fertilizer
Slow-release fertilizers are more expensive and many people are reluctant to use them. The three main
categories of slow-release technologies are: Synthetic Organics, Coatings, and Urea.
Urea materials include Urea Formaldehyde (UF) reaction products. The release of N from UF-reaction
products requires microbial activity. Factors such as temperature and pH can influence the rate of enzymes
and microbial activity and the subsequent release of N. Manufacturing UF materials consists of combining
water-soluble urea and formaldehyde in a reactor under controlled conditions. The main components are
allowed to react for a period of time and then the reaction stops. A heterogeneous mixture of polymers is
produced. The finished product contains some percentage of unreacted urea and varying percentages of UF
polymers such as methylene diurea, trimethylene tetraurea and tetramethylene pentaurea. The exact
combination of urea and polymers makes a product unique. One of the best-known products is Nitroform®
(Blue Chip), with an analysis of 38-0-0.
Poly-methylene urea is a liquid compound that actually delivers its full complement of N over about 8 months
and is completely soluble in water. The fertilizer is non-corrosive, will not settle in the tank, contains no salts,
and is completely biodegradable. Additionally, the product is easier on equipment because there is no grit
involved. Poly-methylene urea is now commercially available with a premixed complement of micro-nutrients
and some ammonium nitrate, and it can even be used as a foliar fertilizer treatment.
IBDU are synthetic organics including materials where N release is determined by a material with low water
solubility. IBDU is the predominant product in this group. It is manufactured much like a urea product only
with a different aldehyde. The N release is regulated by water, not microbes. Once the urea is released it is
converted to ammoniacal N by an enzyme and to the nitrate form of nitrogen by bacteria. It is not affected by
temperature and is therefore a good fertilizer for spring or autumn.
Bio-fertilizers represent a new tool for growing trees that are based on biology. Bio-fertilizers provide slow but
lasting fertilizing effects. Bio-fertilizers are based on living organisms and maintain their beneficial effects as
long as the host trees sustain them. Scientists have isolated various mycorrhizal fungi and beneficial
rhizosphere bacteria, and they have further devised the means to mass-produce bio-fertilizer and to formulate
new products that contain them. The commercial availability of bio fertilizer allows planting sites to possess
the sustainable fertility more characteristic of the natural forest.
Keep in mind that the best fertilizer for trees is water. Trees have the means to gather what nutrients they need from the soil and seldom, if ever need supplemental fertilization.
Fertilizer Label
The labels on containers of fertilizer must carry the specific analysis, which is the weight percentage of the three major nutrients in the fertilizer mix:
- total nitrogen (N),
- available phosphate (P2O5),
- water-soluble potash (K2O).
Total N means the total amount of ammoniacal N, urea N, water insoluble N, and other recognized and determinable forms of N. The N breakdown statement is only required when slow release or organic N properties are claimed or guaranteed.
When reading the label, a 20-10-10 analysis for example, would contain 20% total N, 10% P2O5, and 10% K2O. Therefore, a fifty-pound bag of fertilizer with this analysis would contain ten pounds of total N, five pounds of P2O5, and five pounds of K2O, or a total of twenty pounds of plant food. The other 60% would consist of inert material or minor nutrients. Always read the ingredients and follow all label directions prior to applying fertilizer.
There are many formulations, but the listings are always in the same order, with N first, followed by P2O5, and K2O. The specific fertilizer ratio needed will depend on the soil nutrient level. One general rule can be established: the percentage of N in the formula usually dictates the amount of fertilizer to be applied.
When other plant nutrients in addition to N, P, or K are guaranteed, they must be listed in columnar form immediately below the primary nutrient guarantees and always in the following order with minimum percentages listed: Calcium (Ca); Magnesium (Mg); Sulfur (S); Boron (B); Chlorine (Cl); Cobalt (Co); Copper (Cu); Iron (Fe); Manganese (Mn); Molybdenum (Mo); Sodium (Na); and Zinc (Zn).
Fertilizer Types
There are three types of fertilizers: organic, inorganic, and slow release fertilizer.
1. Organic Fertilizer
The significant difference between natural organics and chemical inorganics is that organisms in the soil must release N into natural organics before it can become food for the tree. Therefore, since they are not soluble in water, they are less likely to be lost through leaching, and they are slow-releasing and non-burning. Natural
organics are usually low in N.
Organic fertilizers are derived from nature, such as manure, sludge, etc., and are marketable in dry form only. There are also synthetic organic fertilizers such as urea formaldehyde and isobutylidene diurea. All of these materials act more slowly than other fertilizers, thus reducing the danger of over-fertilization. However, those
that have a low percentage of N are bulkier and heavier to handle because they must be applied in much
greater quantities. These materials release the fertilizing elements somewhat unpredictably when the soil is
warm.
Bone meal decomposes slowly and thus releases P2O5 slowly. It is a well-known additive at the bottom of the
hole for bulb planting. Another advantage of bone meal is that it helps neutralize the acidity of peat based
potting mixes.
Cottonseed meal is a by-product of cotton manufacturing. It is somewhat acidic in reaction as a fertilizer.
Formulas vary slightly, but are generally 7-3-2. Cottonseed meal is available in warm soils and there is little
danger of over-fertilizing. It is used with acid loving plants.
Fish emulsion is a fertilizer made from fish byproducts. A major disadvantage is the intense odor; however, the
smell will dissipate in a day or two. Fish emulsion is high in N and is a source of several trace elements. It is
excellent for use in the late winter to boost the early growth spurt. It is possible to 'burn' plants if too strong a
solution is applied.
Seaweed is a source of trace metals and growth hormones. Its greatest disadvantage is the high cost. This
form of fertilizer is usually used for houseplants, but experimentation continues for tree and garden use.
Manure comes in several types including horse, cow, pig, chicken, and sheep products. Fresh manures have
the highest concentration of nutrients, but when they are aged or composted, the nutrient content is reduced.
Fresh manure should not be used where it will come into contact with tender roots. Composted forms are
more commonly used to reduce burning the plant roots. Manures are useful for increasing the organic content
of the soil, improving soil structure, and increasing bacterial activity. Manure should be spread evenly and
dug, rototilled, or plowed under.
Sewage sludge or biosolid is a recycled product from municipal sewage treatment plants. Activated sludge
has higher concentrations of nutrients (approximately 6-3-5) compared to composted sludge. It is usually sold
in a dry, granular form for general-purpose use and as a long-lasting, non-burning fertilizer. Composted sludge
is mainly used as a soil additive and has a lower nutrient content (approx. 2-3-0).
2. Inorganic Fertilizer
The blended inorganic fertilizers readily break down in the soil and quickly bring nutrients to the plants. These
fertilizers are soluble in water. They are often termed "hot fertilizers" because they contain salts and various
mineral compounds that can burn tree roots if not handled properly. The chief advantage is that they contain a
high ratio of N, P2O5, and K2O. While inorganic fertilizer supplies nutrients to the soil, it does not feed soil
microorganisms. It is the soil microorganisms that are essential for long-term release of nutrients stored in
organic matter. Inorganic fertilizers are generally used for agricultural crops and turfgrass.
Inorganic fertilizers are chemical or mineral products available in dry or liquid form. The N becomes available
from bacterial action over a longer period of time and thus extends its fertilizing action gradually. Slow-
release pellets, packets, and sticks are available for tree fertilization. These pellets are an acceptable source
of nutrients. However, compared to surface application, they do not provide good lateral movement of
nutrients, are somewhat expensive, and have to be reapplied periodically.
Soluble inorganics include urea, ammonium sulfate, ammonium nitrate, potassium nitrate, and sodium nitrate.
They are inexpensive and have a very high level of N.
3. Slow-Release Fertilizer
Slow-release fertilizers are more expensive and many people are reluctant to use them. The three main
categories of slow-release technologies are: Synthetic Organics, Coatings, and Urea.
- Synthetic Organic Fertilizers are water-soluble and can be taken up by the plant almost immediately. Thus applying too much of this type of fertilizer can damage plants.
- Coatings are a physical barrier made of sulfur or plastic that surrounds a water-soluble fertilizer core.
Sulfur coated urea is coated with plastic. The N is released when microbes feed on the sulfur. The thickness of the coating determines the longevity of the product. The water-soluble center is released by temperature vaporizing the coating. - Polymer-coated urea (PCU) is the most recent advancement in fertilizer technologies. The polymer film, similar to timed-release capsules in drugs, coats the water-soluble urea. Besides urea, these fertilizers may contain muriate of potash, potassium nitrate, and N-phosphorus-potassium substrates. Osmocote™ is the oldest and best know PCU.
Urea materials include Urea Formaldehyde (UF) reaction products. The release of N from UF-reaction
products requires microbial activity. Factors such as temperature and pH can influence the rate of enzymes
and microbial activity and the subsequent release of N. Manufacturing UF materials consists of combining
water-soluble urea and formaldehyde in a reactor under controlled conditions. The main components are
allowed to react for a period of time and then the reaction stops. A heterogeneous mixture of polymers is
produced. The finished product contains some percentage of unreacted urea and varying percentages of UF
polymers such as methylene diurea, trimethylene tetraurea and tetramethylene pentaurea. The exact
combination of urea and polymers makes a product unique. One of the best-known products is Nitroform®
(Blue Chip), with an analysis of 38-0-0.
Poly-methylene urea is a liquid compound that actually delivers its full complement of N over about 8 months
and is completely soluble in water. The fertilizer is non-corrosive, will not settle in the tank, contains no salts,
and is completely biodegradable. Additionally, the product is easier on equipment because there is no grit
involved. Poly-methylene urea is now commercially available with a premixed complement of micro-nutrients
and some ammonium nitrate, and it can even be used as a foliar fertilizer treatment.
IBDU are synthetic organics including materials where N release is determined by a material with low water
solubility. IBDU is the predominant product in this group. It is manufactured much like a urea product only
with a different aldehyde. The N release is regulated by water, not microbes. Once the urea is released it is
converted to ammoniacal N by an enzyme and to the nitrate form of nitrogen by bacteria. It is not affected by
temperature and is therefore a good fertilizer for spring or autumn.
Bio-fertilizers represent a new tool for growing trees that are based on biology. Bio-fertilizers provide slow but
lasting fertilizing effects. Bio-fertilizers are based on living organisms and maintain their beneficial effects as
long as the host trees sustain them. Scientists have isolated various mycorrhizal fungi and beneficial
rhizosphere bacteria, and they have further devised the means to mass-produce bio-fertilizer and to formulate
new products that contain them. The commercial availability of bio fertilizer allows planting sites to possess
the sustainable fertility more characteristic of the natural forest.
Keep in mind that the best fertilizer for trees is water. Trees have the means to gather what nutrients they need from the soil and seldom, if ever need supplemental fertilization.
Fertilizer Myths
A lot has been written about fertilizer, but some of it is wrong.
Myth: Commercial fertilizers are chemicals that are harmful to people and animals.
Fact: Commercial fertilizers are made of natural nutrients that trees can absorb. They are the same minerals as those in the food that people eat.
Myth: Organic fertilizer is better for trees than chemical fertilizers.
Fact: Trees can only use nitrogen in the nitrate form. Organic nitrogen requires the nitrification conversion process by microorganisms to become nitrate. Inorganic fertilizer can provide the nitrate form immediately. Nitrate itself, is the same whether it is from an organic or an inorganic source.
Myth: Organic matter and organic fertilizer are the same thing.
Fact: This is not quite true. Organic matter is soil composed of organic compounds that have come from the remains of once-living organisms such as dead plants and animals and their waste products in the environment. It is digested by bacteria and other organisms. Organic fertilizers contain insoluble nitrogen and act as a slow-release fertilizer. In other words, an organic fertilizer refers to a soil amendment derived from natural sources that increases organic matter in the soil.
Myth: More fertilizer means faster growing trees.
Fact: The practical matter is that soil can only hold on to a certain amount of nutrients at one time. Once the soil is saturated with nutrients, the surplus nutrients just leach out into the groundwater or surface water where it causes eutrification.
Myth: Even with nutrients in the soil, adding more in the form of fertilizer makes plants grow faster?
Fact: Trees use nutrients in the soil so they can grow. Adding fertilizer is actually just replacing what the tree used. Extra fertilizer just sits in the soil unused by trees and usually washed away by groundwater.
Myth: Lots of phosphorus makes lots of flowers.
Fact: Phosphorus does not stimulate flower production or root growth and it also has no apparent relation to winter hardiness. Overloading phosphorus in the soil actually stretches inter-nodes making the trees leggy and weak. It can tie up root intake sites for several other nutrients including nitrogen. It leaches readily and has become one of our major water pollutants. It is true that a cold soil can cause plants to show phosphorus deficiency such as red or purplish discoloration. But this isn't because phosphorus isn't present; the roots simply can't absorb it when the soil is cold.
When fertilizing, read and follow label instructions. Apply these products sparingly and over the root zone. Large amounts may slow the growth of the tree and cause deficiency symptoms of other nutrients.
Myth: Potassium and magnesium will increase cold hardiness of trees.
Fact: Studies have shown that neither mineral affects cold hardiness of plants. Common sources of these minerals are fireplace ashes and Epsom salts. Wood ashes are not beneficial but Epsom salts do make leaves greener and reduce the soil pH briefly, so they might be helpful with cold hardiness, but there is no research proof of this.
Myth: Controlled-release fertilizers release the product at the wrong time.
Fact: This myth is partially correct. All water soluble fertilizers are encapsulated with some form of polymer coating. The release of nutrients and predictability of performance is dependent upon the polymer used in the coating process and each manufacturer has its own formula.
The coating is activated by moisture and the release of nutrients is associated with temperature. The higher the temperature the faster the release. When it is applied in the spring, the release increases with the rising temperatures and this is good. However, if it is applied in autumn, which is fine as the temperature and nutrient release decreases. But, if there is a long-term January thaw, the fertilizer is released and the tree thinks it is spring. The result is major damage to the tree and this is bad.
Myth: Autumn fertilization is bad because it makes wood too soft to tolerate the cold weather.
Fact: Trees that are starved for nutrition as they go into their winter dormancy period will have a greater risk for winter injury than those that have a reserve of nutrients to carry them through. In addition when spring arrives and the trees start their natural growth cycle, those with some nutrient reserves react quickly and make that all important first spurt of growth.
On the other hand, trees that have excess nutrients in autumn are unable to slow down and take advantage of their natural rest period. When the first real cold snap occurs, it freezes the active vascular systems causing the tree major harm.
The best recommendation is to use common sense. It is better to use controlled-release fertilizers that are controlled by temperatures, because they will slow down with the lowering temperatures. Autumn fertilization is fine as long as it is done sparingly. If the controlled-release fertilizer is applied at half or a quarter of the recommend rate, it will carry the trees safely through the winter and still allow them to utilize their reserves for growth in the spring.
A lot has been written about fertilizer, but some of it is wrong.
Myth: Commercial fertilizers are chemicals that are harmful to people and animals.
Fact: Commercial fertilizers are made of natural nutrients that trees can absorb. They are the same minerals as those in the food that people eat.
Myth: Organic fertilizer is better for trees than chemical fertilizers.
Fact: Trees can only use nitrogen in the nitrate form. Organic nitrogen requires the nitrification conversion process by microorganisms to become nitrate. Inorganic fertilizer can provide the nitrate form immediately. Nitrate itself, is the same whether it is from an organic or an inorganic source.
Myth: Organic matter and organic fertilizer are the same thing.
Fact: This is not quite true. Organic matter is soil composed of organic compounds that have come from the remains of once-living organisms such as dead plants and animals and their waste products in the environment. It is digested by bacteria and other organisms. Organic fertilizers contain insoluble nitrogen and act as a slow-release fertilizer. In other words, an organic fertilizer refers to a soil amendment derived from natural sources that increases organic matter in the soil.
Myth: More fertilizer means faster growing trees.
Fact: The practical matter is that soil can only hold on to a certain amount of nutrients at one time. Once the soil is saturated with nutrients, the surplus nutrients just leach out into the groundwater or surface water where it causes eutrification.
Myth: Even with nutrients in the soil, adding more in the form of fertilizer makes plants grow faster?
Fact: Trees use nutrients in the soil so they can grow. Adding fertilizer is actually just replacing what the tree used. Extra fertilizer just sits in the soil unused by trees and usually washed away by groundwater.
Myth: Lots of phosphorus makes lots of flowers.
Fact: Phosphorus does not stimulate flower production or root growth and it also has no apparent relation to winter hardiness. Overloading phosphorus in the soil actually stretches inter-nodes making the trees leggy and weak. It can tie up root intake sites for several other nutrients including nitrogen. It leaches readily and has become one of our major water pollutants. It is true that a cold soil can cause plants to show phosphorus deficiency such as red or purplish discoloration. But this isn't because phosphorus isn't present; the roots simply can't absorb it when the soil is cold.
When fertilizing, read and follow label instructions. Apply these products sparingly and over the root zone. Large amounts may slow the growth of the tree and cause deficiency symptoms of other nutrients.
Myth: Potassium and magnesium will increase cold hardiness of trees.
Fact: Studies have shown that neither mineral affects cold hardiness of plants. Common sources of these minerals are fireplace ashes and Epsom salts. Wood ashes are not beneficial but Epsom salts do make leaves greener and reduce the soil pH briefly, so they might be helpful with cold hardiness, but there is no research proof of this.
Myth: Controlled-release fertilizers release the product at the wrong time.
Fact: This myth is partially correct. All water soluble fertilizers are encapsulated with some form of polymer coating. The release of nutrients and predictability of performance is dependent upon the polymer used in the coating process and each manufacturer has its own formula.
The coating is activated by moisture and the release of nutrients is associated with temperature. The higher the temperature the faster the release. When it is applied in the spring, the release increases with the rising temperatures and this is good. However, if it is applied in autumn, which is fine as the temperature and nutrient release decreases. But, if there is a long-term January thaw, the fertilizer is released and the tree thinks it is spring. The result is major damage to the tree and this is bad.
Myth: Autumn fertilization is bad because it makes wood too soft to tolerate the cold weather.
Fact: Trees that are starved for nutrition as they go into their winter dormancy period will have a greater risk for winter injury than those that have a reserve of nutrients to carry them through. In addition when spring arrives and the trees start their natural growth cycle, those with some nutrient reserves react quickly and make that all important first spurt of growth.
On the other hand, trees that have excess nutrients in autumn are unable to slow down and take advantage of their natural rest period. When the first real cold snap occurs, it freezes the active vascular systems causing the tree major harm.
The best recommendation is to use common sense. It is better to use controlled-release fertilizers that are controlled by temperatures, because they will slow down with the lowering temperatures. Autumn fertilization is fine as long as it is done sparingly. If the controlled-release fertilizer is applied at half or a quarter of the recommend rate, it will carry the trees safely through the winter and still allow them to utilize their reserves for growth in the spring.
Soil pH
Soil pH is a measure of acidity or alkalinity in soil, represented by a number on a scale on which 1 is very acidic, 7 is neutral, and 14 is extremely alkaline. For optimum plant growth, efforts should focus on maintaining a nearly neutral soil pH. "pH" means the power of Hydrogen and is a measurement of hydrogen atoms in the soil. Acidic soil contains many H+ ions and alkaline soil contains many hydrogen oxide or hydroxide (OH–) ions.
The most accurate method of determining soil pH is by a pH meter. Secondary methods, which are simple and easy but less accurate than using a pH meter, consists of using certain indicator paper strips or indicator dyes and matching the color to a known pH level.
Soil pH Formation
Under conditions in which rainfall exceeds leaching, the basic soil cations (Ca, Mg, K) are gradually depleted and replaced with cations held in colloidal soil reserves, leading to soil acidity. The woodland floor is carpeted in needles of conifers, leaves of hardwood trees, and other dead plant matter, most of which increase soil acidity as they decompose. Unless this woodland is on top of a huge deposit of alkaline material such as limestone or serpentine, the soil will tend to be slightly acidic.
Importance
Soil pH is important because it influences plant growth, beneficial bacteria growth, nutrient availability, toxic elements, and soil structure:
The pH is not an indication of fertility, but it affects the solubility and availability of nutrients to be taken up by microorganisms and plant roots. A soil may contain adequate nutrients, yet growth may be limited by a very unfavorable pH. Likewise, builder's sand, which is virtually devoid of nutrients, may have an optimum pH for certain plant growth. Descriptive terms commonly associated with certain ranges in soil pH and the pH ranges of common products are:
Soils tend to become acidic as a result of:
How to Correct pH
Normally, limestone (calcium carbonate), dolomitic limestone (calcium carbonate and magnesium carbonate), burnt lime (calcium oxide), or slaked lime (calcium hydroxide) are used to increase the pH, or "sweeten" the soil. Limestone and dolomitic limestone are less likely to "burn" plant roots, while burnt and slaked lime are not recommended around plants. The amount of these materials necessary to change the pH will depend on the soil type. The greater the amount of organic matter or clay in a soil, the more limestone or dolomitic limestone will be required to raise the pH. Table 1 shows the amounts of limestone needed to raise the pH to a pH level of 6.5.
Table 1
Pounds of limestone per 100 sq. ft.
Sandy loam Loam Clay
From pH 4.5 to 6.5 12.6 25.3 34.8
From pH 5.0 to 6.5 10.6 21.2 29.0
From pH 5.5 to 6.5 4.2 8.4 11.6
From pH 6.0 to 6.5 1.7 3.3 4.5
If a soil is tested as too alkaline, determine if this is due to recent application of limestone or whether it is due to an inherent characteristic of the soil. It is quite difficult, if not impossible, to appreciably change the pH of naturally alkaline soil by use of acid-forming materials. If a high pH is due to applied limestone or other alkaline additives, ammonium sulfate, sulfur, or similar acid-forming materials can be applied. Table 2 shows the amounts of sulfur needed to lower the pH.
Table 2
Pounds of sulfur per 100 square feet needed to lower the pH
To pH 6.5 To pH 6.0 To pH 5.5 To pH 5.0
From pH 8.0 3.0 4.0 5.5 7.0
From pH 7.5 2.0 3.5 5.0 6.5
From pH 7.0 1.0 2.0 3.5 5.0
From pH 6.5 None 1.0 2.5 4.0
Not more than 1 pound (0.46 kg) of sulfur per 100 sq. ft. (9 sq. m.) should be applied in one treatment. If the soil is clay loam, heavier applications of sulfur will be necessary. Repeated applications of sulfur should not be made more often than once every 8 weeks. Sulfur oxidizes in the soil and mixes with water to form a strong acid that can burn the roots of plants and should be used with caution. It is easier to raise the pH of soil than it is to lower it.
Organic Matter Effect
As organic matter decomposes, minerals are slowly converted to salts that dissolve in water and become available for plant roots to absorb. Using overly acidic compost won't usually do any long-term damage to the soil, but using one that's too alkaline might. Regular applications of good-quality compost help maintain neutral soil pH. High-pH composts often contain carbonates, usually in the form of limestone (calcium carbonate). In naturally alkaline soil (most common in drier regions), avoid using high-pH compost because other nutrients, such as phosphorus and zinc, will become unavailable.
Tree Growth
Trees grow within a limited range of pH values. It is difficult to change the pH in a landscape situation as compared to an agricultural situation where the soil is turned frequently and soil amendments are easily added. In the landscape situation, limestone or sulfur can be conveniently added only during the installation process. Therefore, it is better to install trees that tolerate the existing pH rather than trying to change it after the installation, unless the entire root zone is replaced with soil having the desired pH. To do otherwise may result in nutrient deficiencies that would affect plant growth and survival.
Trees Installed in Alkaline Soil
Trees that are tolerant of alkalinity can get their needed nutrients through a process that acidifies the soil around their roots. At installation time, include well-decomposed organic matter and soil sulfur in the planting mix of an over-sized installation hole. The organic matter naturally tends to moderate the alkaline conditions, especially over time.
Sulfur is only available in pellet form. When intact, the pellet has a limited effect and is overly concentrated in that spot. To counter this condition, add the sulfur to the backfill piles and turn the pile once. The pile must be at least somewhat moist. Allow the pile to sit for a few hours so the soil moistens the sulfur pellets and the sulfur becomes softer and prone to disintegration. When the soil is turned a second time and again in the installation hole, the pellets break apart and disintegrate. This process of allowing the sulfur to soften greatly enhances its effectiveness.
The final step in the process of creating and maintaining better soil pH levels in our environment is in the use of organic mulch. The moderating effects of this soil treatment are slow and gradual, but are profound. Even if we properly prepare soils, with alkaline irrigation water any moderating effects are eventually lost and pH levels begin to climb again. The use of the organic (usually wood-chip) mulches counters this natural and inevitable climb in pH levels and helps to build and maintain soils that are nutrient rich, dark, pliable and of course, of lower pH.
Instead of trying to correct the soil, it is much more cost effective and sustainable to grow trees that will tolerate alkaline soil such as those on the second list below. One recent development for growing trees in alkaline soils is the introduction of Redpointe Maple Acer rubrum ‘Frank Jr.’ PP 16769. This tree was selected for its beauty and size as well as its extreme resistance to chlorosis in high pH soils. Expect to see similar alkaline tolerant trees to be introduced in the future.
Trees that Tolerate Soil More Acidic than pH 4
Scientific name Common name
Abies spp. Fir
Betula nigra River birch
Carpinus betulus European hornbeam
Chamaecyparis obtusa Hinoki false cypress
Chionanthus virginicus Fringe tree
Cornus florida Dogwood
Crataegus mexicana Mexican hawthorn
Cupressus lindleyi White cedar
Fagus grandifolia American beech
Franklinia altamaha Franklinia
Gordonia lasianthus Gordonia
Grevillea robusta Silk oak
Halesia tetraptera Carolina Silverbell
Ilex verticillata Winterberry
Jacaranda mimosifolia Jacaranda
Liquidambar styraciflua Sweetgum
Maackia amurensis Maackia
Magnolia virginiana Sweet bay
Oxydendrum arboreum Sourwood
Pinus rigida Pitch pine
Quercus spp. Oak (especially pin oak)
Sassafras albidum Sassafras
Stewartia pseudocamellia Japanese Stewartia
Styrax japonicus Japanese snowbell
Symplocos paniculata Asiatic sweetleaf
Taxodium mucronatum Montezuma baldcypress
Taxus canadensis Canada yew
Tsuga spp. Hemlock
Trees that Tolerate Soil more Alkaline than pH 8
Scientific name Common name
Abies spp. Fir
Acacia longifolia Acacia
Acer spp. Maple
Aesculus spp. Horsechestnut
Amelanchier spp. Serviceberry
Asimina triloba Pawpaw
Betula spp. Birch
Carpinus spp. Hornbeam
Casuarina equisetifolia Australian pine
Celtis australis Mediterranean hackberry
Celtis occidentalis Hackberry
Cercidiphyllum japonicum Katsura
Cercis canadensis American redbud
Chamaecyparis spp. Cypress
Cladrastis lutea Yellowwood
Cornus kousa Kousa dogwood
Davidia involucrate Handkerchief tree
Eucommia ulmoides Hardy rubber tree
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Hamamelis virginiana Witch hazel
Holodiscus discolor Holodiscus
Kalopanax pictus Castor-aralia
Koelreuteria paniculata Golden rain tree
Laburnum x watereri Goldenchain
Liquidambar styraciflua Sweetgum
Lonicera tatarica Tartarian honeysuckle
Maackia amurensis Maackia
Magnolia spp. Magnolia
Malus spp. Crabapple
Nyssa sylvatica Tupelo
Ostrya virginiana American hop hornbeam
Phellodendron amurense Amur corktree
Pinus spp. Pine
Prunus spp. Cherry, plum
Pseudotsuga menziesii Douglas fir
Pyrus calleryana Callery pear
Quercus macrocarpa Bur oak
Quercus muhlengergii Chinquapin oak
Phoenix canariensis Canary Island date palm
Platanus x acerifolia London plane tree
Platanus occidentalis American sycamore
Robinia pseudoacacia Black locust
Sciadophitys verticillata Umbrella pine
Styphnolobium japonica Scholar tree
Syringa spp. Lilac
Tamarix gallica Tamarix
Taxodium distichum Bald cypress
Tilia spp. Linden
Ulmus spp. Elm
Washingtonia robusta Mexican fan palm
Zelkova serrata Japanese Zelkova
Soil pH is a measure of acidity or alkalinity in soil, represented by a number on a scale on which 1 is very acidic, 7 is neutral, and 14 is extremely alkaline. For optimum plant growth, efforts should focus on maintaining a nearly neutral soil pH. "pH" means the power of Hydrogen and is a measurement of hydrogen atoms in the soil. Acidic soil contains many H+ ions and alkaline soil contains many hydrogen oxide or hydroxide (OH–) ions.
The most accurate method of determining soil pH is by a pH meter. Secondary methods, which are simple and easy but less accurate than using a pH meter, consists of using certain indicator paper strips or indicator dyes and matching the color to a known pH level.
Soil pH Formation
Under conditions in which rainfall exceeds leaching, the basic soil cations (Ca, Mg, K) are gradually depleted and replaced with cations held in colloidal soil reserves, leading to soil acidity. The woodland floor is carpeted in needles of conifers, leaves of hardwood trees, and other dead plant matter, most of which increase soil acidity as they decompose. Unless this woodland is on top of a huge deposit of alkaline material such as limestone or serpentine, the soil will tend to be slightly acidic.
Importance
Soil pH is important because it influences plant growth, beneficial bacteria growth, nutrient availability, toxic elements, and soil structure:
- A pH determination (soil test) will tell whether the soil will produce good plant growth or whether it will need to be treated to adjust the pH level. For most plants, the optimum pH range is from 5.5 to 7.0, but certain trees prefer a more acidic soil and others may require a more alkaline level.
- Bacterial activity that releases nitrogen from organic matter and certain fertilizers is particularly affected by soil pH, because bacteria function best in the pH range of 5.5 to 7.0.
- Plant nutrients leach out of soils with a pH below 5.0 much more rapidly than from soils with values between 5.0 and 7.5 and is generally most available to plants in the range of 5.5 to 6.5.
- Aluminum, iron, and manganese may become toxic to plant growth in certain soils with a pH below 5.0.
- The structure of the soil is affected by pH. Clay soils for example, are granular and are easily worked at the optimum pH range (5.5 to 7.0), but if the soil pH is either extremely acid or extremely alkaline, clays
tend to become sticky and hard to cultivate. - Raising the pH will add calcium and reduce the effects of calcium leaching.
- Raising the pH will also raise phosphorus, molybdenum, and magnesium levels.
The pH is not an indication of fertility, but it affects the solubility and availability of nutrients to be taken up by microorganisms and plant roots. A soil may contain adequate nutrients, yet growth may be limited by a very unfavorable pH. Likewise, builder's sand, which is virtually devoid of nutrients, may have an optimum pH for certain plant growth. Descriptive terms commonly associated with certain ranges in soil pH and the pH ranges of common products are:
- Extremely acid - lower than pH 4.5; lemon-2.5; vinegar-3.0; stomach acid-2.0; soda-2.0-4.0
- Very strongly acid - pH 4.5 to 5.0; beer-4.5-5.0; tomatoes-4.5
- Strongly acid - pH 5.1- to 5.5; carrots-5.0; asparagus-5.5; boric acid-5.2; cabbage-5.3
- Moderately acid - pH 5.6 to 6.0; potatoes-5.6
- Slightly acid - pH 6.1 to 6.5; salmon-6.2; cow's milk-6.5
- Neutral - pH 6.6 to 7.3; saliva-6.6-7.3; blood-7.3; shrimp-7.0
- Slightly alkaline - pH 7.4 to 7.8; eggs-7.6-7.8
- Moderately alkaline - pH 7.9 to 8.4; sea water-8.2; sodium bicarbonate-8.4
- Strongly alkaline - pH 8.5 to 9.0; borax-9.0
- Very strongly alkaline - higher than pH 9.1; milk of magnesia-10.5, ammonia-11.1; limestone-12
Soils tend to become acidic as a result of:
- rainwater leaching away basic ions (calcium, magnesium, potassium, and sodium),
- the formation of strong organic and inorganic acids, such as nitric acid and sulfuric acid, from decaying organic matter and oxidation of ammonium and sulfur fertilizers. Strongly acid soils are usually the result of the action of these strong organic and inorganic acids.
How to Correct pH
Normally, limestone (calcium carbonate), dolomitic limestone (calcium carbonate and magnesium carbonate), burnt lime (calcium oxide), or slaked lime (calcium hydroxide) are used to increase the pH, or "sweeten" the soil. Limestone and dolomitic limestone are less likely to "burn" plant roots, while burnt and slaked lime are not recommended around plants. The amount of these materials necessary to change the pH will depend on the soil type. The greater the amount of organic matter or clay in a soil, the more limestone or dolomitic limestone will be required to raise the pH. Table 1 shows the amounts of limestone needed to raise the pH to a pH level of 6.5.
Table 1
Pounds of limestone per 100 sq. ft.
Sandy loam Loam Clay
From pH 4.5 to 6.5 12.6 25.3 34.8
From pH 5.0 to 6.5 10.6 21.2 29.0
From pH 5.5 to 6.5 4.2 8.4 11.6
From pH 6.0 to 6.5 1.7 3.3 4.5
If a soil is tested as too alkaline, determine if this is due to recent application of limestone or whether it is due to an inherent characteristic of the soil. It is quite difficult, if not impossible, to appreciably change the pH of naturally alkaline soil by use of acid-forming materials. If a high pH is due to applied limestone or other alkaline additives, ammonium sulfate, sulfur, or similar acid-forming materials can be applied. Table 2 shows the amounts of sulfur needed to lower the pH.
Table 2
Pounds of sulfur per 100 square feet needed to lower the pH
To pH 6.5 To pH 6.0 To pH 5.5 To pH 5.0
From pH 8.0 3.0 4.0 5.5 7.0
From pH 7.5 2.0 3.5 5.0 6.5
From pH 7.0 1.0 2.0 3.5 5.0
From pH 6.5 None 1.0 2.5 4.0
Not more than 1 pound (0.46 kg) of sulfur per 100 sq. ft. (9 sq. m.) should be applied in one treatment. If the soil is clay loam, heavier applications of sulfur will be necessary. Repeated applications of sulfur should not be made more often than once every 8 weeks. Sulfur oxidizes in the soil and mixes with water to form a strong acid that can burn the roots of plants and should be used with caution. It is easier to raise the pH of soil than it is to lower it.
Organic Matter Effect
As organic matter decomposes, minerals are slowly converted to salts that dissolve in water and become available for plant roots to absorb. Using overly acidic compost won't usually do any long-term damage to the soil, but using one that's too alkaline might. Regular applications of good-quality compost help maintain neutral soil pH. High-pH composts often contain carbonates, usually in the form of limestone (calcium carbonate). In naturally alkaline soil (most common in drier regions), avoid using high-pH compost because other nutrients, such as phosphorus and zinc, will become unavailable.
Tree Growth
Trees grow within a limited range of pH values. It is difficult to change the pH in a landscape situation as compared to an agricultural situation where the soil is turned frequently and soil amendments are easily added. In the landscape situation, limestone or sulfur can be conveniently added only during the installation process. Therefore, it is better to install trees that tolerate the existing pH rather than trying to change it after the installation, unless the entire root zone is replaced with soil having the desired pH. To do otherwise may result in nutrient deficiencies that would affect plant growth and survival.
Trees Installed in Alkaline Soil
Trees that are tolerant of alkalinity can get their needed nutrients through a process that acidifies the soil around their roots. At installation time, include well-decomposed organic matter and soil sulfur in the planting mix of an over-sized installation hole. The organic matter naturally tends to moderate the alkaline conditions, especially over time.
Sulfur is only available in pellet form. When intact, the pellet has a limited effect and is overly concentrated in that spot. To counter this condition, add the sulfur to the backfill piles and turn the pile once. The pile must be at least somewhat moist. Allow the pile to sit for a few hours so the soil moistens the sulfur pellets and the sulfur becomes softer and prone to disintegration. When the soil is turned a second time and again in the installation hole, the pellets break apart and disintegrate. This process of allowing the sulfur to soften greatly enhances its effectiveness.
The final step in the process of creating and maintaining better soil pH levels in our environment is in the use of organic mulch. The moderating effects of this soil treatment are slow and gradual, but are profound. Even if we properly prepare soils, with alkaline irrigation water any moderating effects are eventually lost and pH levels begin to climb again. The use of the organic (usually wood-chip) mulches counters this natural and inevitable climb in pH levels and helps to build and maintain soils that are nutrient rich, dark, pliable and of course, of lower pH.
Instead of trying to correct the soil, it is much more cost effective and sustainable to grow trees that will tolerate alkaline soil such as those on the second list below. One recent development for growing trees in alkaline soils is the introduction of Redpointe Maple Acer rubrum ‘Frank Jr.’ PP 16769. This tree was selected for its beauty and size as well as its extreme resistance to chlorosis in high pH soils. Expect to see similar alkaline tolerant trees to be introduced in the future.
Trees that Tolerate Soil More Acidic than pH 4
Scientific name Common name
Abies spp. Fir
Betula nigra River birch
Carpinus betulus European hornbeam
Chamaecyparis obtusa Hinoki false cypress
Chionanthus virginicus Fringe tree
Cornus florida Dogwood
Crataegus mexicana Mexican hawthorn
Cupressus lindleyi White cedar
Fagus grandifolia American beech
Franklinia altamaha Franklinia
Gordonia lasianthus Gordonia
Grevillea robusta Silk oak
Halesia tetraptera Carolina Silverbell
Ilex verticillata Winterberry
Jacaranda mimosifolia Jacaranda
Liquidambar styraciflua Sweetgum
Maackia amurensis Maackia
Magnolia virginiana Sweet bay
Oxydendrum arboreum Sourwood
Pinus rigida Pitch pine
Quercus spp. Oak (especially pin oak)
Sassafras albidum Sassafras
Stewartia pseudocamellia Japanese Stewartia
Styrax japonicus Japanese snowbell
Symplocos paniculata Asiatic sweetleaf
Taxodium mucronatum Montezuma baldcypress
Taxus canadensis Canada yew
Tsuga spp. Hemlock
Trees that Tolerate Soil more Alkaline than pH 8
Scientific name Common name
Abies spp. Fir
Acacia longifolia Acacia
Acer spp. Maple
Aesculus spp. Horsechestnut
Amelanchier spp. Serviceberry
Asimina triloba Pawpaw
Betula spp. Birch
Carpinus spp. Hornbeam
Casuarina equisetifolia Australian pine
Celtis australis Mediterranean hackberry
Celtis occidentalis Hackberry
Cercidiphyllum japonicum Katsura
Cercis canadensis American redbud
Chamaecyparis spp. Cypress
Cladrastis lutea Yellowwood
Cornus kousa Kousa dogwood
Davidia involucrate Handkerchief tree
Eucommia ulmoides Hardy rubber tree
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Hamamelis virginiana Witch hazel
Holodiscus discolor Holodiscus
Kalopanax pictus Castor-aralia
Koelreuteria paniculata Golden rain tree
Laburnum x watereri Goldenchain
Liquidambar styraciflua Sweetgum
Lonicera tatarica Tartarian honeysuckle
Maackia amurensis Maackia
Magnolia spp. Magnolia
Malus spp. Crabapple
Nyssa sylvatica Tupelo
Ostrya virginiana American hop hornbeam
Phellodendron amurense Amur corktree
Pinus spp. Pine
Prunus spp. Cherry, plum
Pseudotsuga menziesii Douglas fir
Pyrus calleryana Callery pear
Quercus macrocarpa Bur oak
Quercus muhlengergii Chinquapin oak
Phoenix canariensis Canary Island date palm
Platanus x acerifolia London plane tree
Platanus occidentalis American sycamore
Robinia pseudoacacia Black locust
Sciadophitys verticillata Umbrella pine
Styphnolobium japonica Scholar tree
Syringa spp. Lilac
Tamarix gallica Tamarix
Taxodium distichum Bald cypress
Tilia spp. Linden
Ulmus spp. Elm
Washingtonia robusta Mexican fan palm
Zelkova serrata Japanese Zelkova
Soil Conditioners
A soil's physical condition is one factor that can limit tree growth. Poor soil can restrict water intake into a tree and subsequent water movement, root development, and aeration of the soil. Arborists, landscape architects, nurseries, and researchers alike are interested in improving the physical condition of soil to enhance tree growth. These goals can be accomplished in part through the use of good management techniques. In addition, there are amending materials and soil conditioners that can be used to improve the soil.
One of the best things to do is to add soil conditioners. These are not chemical conditioners but are products such as manure, compost, peat moss, and leaves. All of the soil conditioners are put on top of the soil about 2 - 3 inches (5 - 8 cm) deep and then mixed into the soil by natural actions such as by earth worms and soil microorganisms.
Soil Conditioners
Soil conditioners are not new and vary greatly in their composition, application rate, and expected or claimed mode of action. Claims for various products include, but are not limited to:
Changing Soil Physical Properties
Soil conditioners will not behave in the same manner and with the same results on all soil types. Different soil types vary greatly in the physical, chemical, and biological properties that influence the effectiveness of soil conditioners. For instance, gypsum may improve infiltration on high-sodium soils but may be of no benefit on non-sodic soils or soils already high in gypsum. The addition of large amounts of organic material will be more effective on soils very low in organic matter than on soils with a higher level of organic matter. The recommended application rates of soil conditioners range from less than a pound (½ kg) per acre for some synthetic or biological soil conditioners to several tons per acre for compost or manure.
Soil conditioners vary in both their origin and composition. Soil conditioners can be organic or inorganic, synthetic or naturally occurring. Because of this diversity of soil conditioners, it is important to understand the nature, use, and practical benefits of these products.
Organic Soil Conditioners
The beneficial effects of organic matter in the improvement of a soil's physical properties have long been known. Organic matter serves as a reservoir for nutrients, and improves soil structure, drainage, aeration, cation exchange capacity, buffering capacity, and water-holding capacity. It also provides a source of food for beneficial microorganisms. Generally speaking, soils high in organic matter have better physical conditions compared to soils low in organic matter.
Organic matter includes plant and animal residues at various stages of decomposition, cells and tissues of organisms, and compounds synthesized by soil organisms. Organic matter contains a wide array of compounds ranging from fats, carbohydrates, and proteins to high molecular weight humic and fulvic acids. Both the diversity of compounds and the interaction of the different compounds contribute to the beneficial effect attributed to organic matter.
Organic matter is usually less than 10% of the total weight of mineral soils. To actually change the organic matter content of a soil, very large amounts of organic materials must be applied. Research has shown that it takes 5 – 15 pounds (2 – 7 kg) of fresh plant residue to produce 1 pound (½ kg) of stable humus within a given area.
Humus and Humic Acid
Natural composting in the forest soil creates humus, the organic material that results from the decomposition of dead organisms, and it contains humic acids. In a vertical cross section of forest soil, the humic layer is the rich, dark layer between the bottom of the topsoil and the top of the parent soil. Humic acids slow decomposition reactions in soils. Humic and fulvic acids buffer pH swings in the soil. Humic acids are very complex and easily immobilized by soil mineral matter. Humic acids can improve germination of fungi, but the germinated fungus has to rapidly find a root to colonize or it will die. Humic acid is the result of biological decay and can no longer be further decomposed.
Humate
Humates are mineral salts of humic and fulvic acids. Commercial humates are products derived from oxidized lignite, an earthy, coal-like substance associated with lignite outcrops. Oxidized lignite often occurs in shallow deposits and usually overlay soft coal deposits. Humates marketed for agricultural purposes may be soluble or insoluble and maybe fortified with commercial fertilizer. Commercial humates contain between 30 – 60% humic acids. Commercial humates do not resemble soil organic matter and therefore cannot be expected to perform the same function. In addition, the low rate of application normally recommended is insignificant in comparison with organic matter already present in most soils. Mixed humates contain 1.2 – 1.5% nitrogen, of which only a small portion is available to a tree within a given year. At the recommended application rate, commercial humates would add less than 1 pound (0.5 kg) of nitrogen per acre.
Animal Manures
Animal manures can contribute significantly to soil organic matter levels and supply various nutrients. Manure contains partially decomposed plant material plus a wide variety of organisms. Many of the organic compounds in manure are similar to those found in soil organic matter. Manure, however, contains soluble salts, which can be detrimental to soil physical properties and tree growth when added in high amounts, especially to arid soils. It is recommended that animal manures be composted for several months to a year before they are applied to the soil for the benefit of plants and trees.
Other Organic Conditioners
Other materials that can serve as soil conditioners include crop residues, compost, sewage sludge, green manure crops, and sawdust. The effectiveness of the material varies upon the amount of material added to the soil. Sewage sludge may contain potentially harmful levels of heavy metals and other toxic materials and should be analyzed for these materials before using near food crops. Even trees in the forest have been harmed by the addition of sewage sludge to the surface of the soil. Sewage treatment plants have been known to dispose of their liquids on a forest floor, thinking it was a fertilizer for the trees, but it was actually harmful.
Synthetic Binding Agents
Several polymers have been shown to improve various soil physical properties. Polymers received a lot of attention in the 1950s when a particular polymer (Krilium) was marketed. The product was shown to improve physical properties and crop yields on certain soils. However, the application rate at which the benefits were found was not economical and interest in this polymer has declined.
Recently, new polymers applied at much lower rates have been promoted as soil conditioners. These polymers include natural polysaccharides, anionic and cationic polymers, and polyacrylamides. The compounds are long-chain, polymeric organic compounds that have a very high-molecular weight. Polymers bind particles together and form stable aggregates. Research is being conducted to identify polymer types as well as application methods and rates to maintain or improve the physical conditions of different soils. Results to date, under field conditions at low rates of application, have not shown consistent, significant improvement in a soil's physical condition.
Mineral Conditioners
Gypsum – has long been recognized for its benefits on high-sodium-containing soils. As mentioned above, gypsum is a mineral that occurs in nature as soft crystalline rock and varies in purity. Gypsum has been shown to displace exchangeable sodium from the cation exchange sites of soils high in sodium. On irrigated or dry land, gypsum can be used to reclaim saline areas or slick spots, soften and crumble alkali hard pans, supply calcium on low-exchange-capacity soils, and improve infiltration for some puddled soils. Gypsum is not recommended on soils containing native gypsum or areas irrigated with water containing abundant amounts of calcium and magnesium. The amount of gypsum to apply depends on the purity of the gypsum and the quantity of sodium present in the soil. Actual rates should be based on the results of a salt-alkali soil test.
Limestone – is crushed rock and other products high in calcium and/or magnesium that will improve the physical condition of some soils, when applied at several tons per acre. However, no consistent response for improving a soil's physical condition has been documented. Most of these products at the rates recommended will not supply enough calcium and/or magnesium to change the cation composition of the soil exchange complex. Several other categories of soil conditioners, including surfactants, such as ammonium alkyl ether sulfate, are claimed to improve soil physical properties, but researchers are still evaluating them.
A soil's physical condition is one factor that can limit tree growth. Poor soil can restrict water intake into a tree and subsequent water movement, root development, and aeration of the soil. Arborists, landscape architects, nurseries, and researchers alike are interested in improving the physical condition of soil to enhance tree growth. These goals can be accomplished in part through the use of good management techniques. In addition, there are amending materials and soil conditioners that can be used to improve the soil.
One of the best things to do is to add soil conditioners. These are not chemical conditioners but are products such as manure, compost, peat moss, and leaves. All of the soil conditioners are put on top of the soil about 2 - 3 inches (5 - 8 cm) deep and then mixed into the soil by natural actions such as by earth worms and soil microorganisms.
Soil Conditioners
Soil conditioners are not new and vary greatly in their composition, application rate, and expected or claimed mode of action. Claims for various products include, but are not limited to:
- improved soil structure and aeration,
- increased water-holding capacity,
- increased availability of water to plants,
- reduced compaction and hardpan conditions,
- improved drainage,
- alkali soil reclamation,
- release of "locked" nutrients,
- better chemical incorporation,
- better root development,
- higher yields and quality.
Changing Soil Physical Properties
Soil conditioners will not behave in the same manner and with the same results on all soil types. Different soil types vary greatly in the physical, chemical, and biological properties that influence the effectiveness of soil conditioners. For instance, gypsum may improve infiltration on high-sodium soils but may be of no benefit on non-sodic soils or soils already high in gypsum. The addition of large amounts of organic material will be more effective on soils very low in organic matter than on soils with a higher level of organic matter. The recommended application rates of soil conditioners range from less than a pound (½ kg) per acre for some synthetic or biological soil conditioners to several tons per acre for compost or manure.
Soil conditioners vary in both their origin and composition. Soil conditioners can be organic or inorganic, synthetic or naturally occurring. Because of this diversity of soil conditioners, it is important to understand the nature, use, and practical benefits of these products.
Organic Soil Conditioners
The beneficial effects of organic matter in the improvement of a soil's physical properties have long been known. Organic matter serves as a reservoir for nutrients, and improves soil structure, drainage, aeration, cation exchange capacity, buffering capacity, and water-holding capacity. It also provides a source of food for beneficial microorganisms. Generally speaking, soils high in organic matter have better physical conditions compared to soils low in organic matter.
Organic matter includes plant and animal residues at various stages of decomposition, cells and tissues of organisms, and compounds synthesized by soil organisms. Organic matter contains a wide array of compounds ranging from fats, carbohydrates, and proteins to high molecular weight humic and fulvic acids. Both the diversity of compounds and the interaction of the different compounds contribute to the beneficial effect attributed to organic matter.
Organic matter is usually less than 10% of the total weight of mineral soils. To actually change the organic matter content of a soil, very large amounts of organic materials must be applied. Research has shown that it takes 5 – 15 pounds (2 – 7 kg) of fresh plant residue to produce 1 pound (½ kg) of stable humus within a given area.
Humus and Humic Acid
Natural composting in the forest soil creates humus, the organic material that results from the decomposition of dead organisms, and it contains humic acids. In a vertical cross section of forest soil, the humic layer is the rich, dark layer between the bottom of the topsoil and the top of the parent soil. Humic acids slow decomposition reactions in soils. Humic and fulvic acids buffer pH swings in the soil. Humic acids are very complex and easily immobilized by soil mineral matter. Humic acids can improve germination of fungi, but the germinated fungus has to rapidly find a root to colonize or it will die. Humic acid is the result of biological decay and can no longer be further decomposed.
Humate
Humates are mineral salts of humic and fulvic acids. Commercial humates are products derived from oxidized lignite, an earthy, coal-like substance associated with lignite outcrops. Oxidized lignite often occurs in shallow deposits and usually overlay soft coal deposits. Humates marketed for agricultural purposes may be soluble or insoluble and maybe fortified with commercial fertilizer. Commercial humates contain between 30 – 60% humic acids. Commercial humates do not resemble soil organic matter and therefore cannot be expected to perform the same function. In addition, the low rate of application normally recommended is insignificant in comparison with organic matter already present in most soils. Mixed humates contain 1.2 – 1.5% nitrogen, of which only a small portion is available to a tree within a given year. At the recommended application rate, commercial humates would add less than 1 pound (0.5 kg) of nitrogen per acre.
Animal Manures
Animal manures can contribute significantly to soil organic matter levels and supply various nutrients. Manure contains partially decomposed plant material plus a wide variety of organisms. Many of the organic compounds in manure are similar to those found in soil organic matter. Manure, however, contains soluble salts, which can be detrimental to soil physical properties and tree growth when added in high amounts, especially to arid soils. It is recommended that animal manures be composted for several months to a year before they are applied to the soil for the benefit of plants and trees.
Other Organic Conditioners
Other materials that can serve as soil conditioners include crop residues, compost, sewage sludge, green manure crops, and sawdust. The effectiveness of the material varies upon the amount of material added to the soil. Sewage sludge may contain potentially harmful levels of heavy metals and other toxic materials and should be analyzed for these materials before using near food crops. Even trees in the forest have been harmed by the addition of sewage sludge to the surface of the soil. Sewage treatment plants have been known to dispose of their liquids on a forest floor, thinking it was a fertilizer for the trees, but it was actually harmful.
Synthetic Binding Agents
Several polymers have been shown to improve various soil physical properties. Polymers received a lot of attention in the 1950s when a particular polymer (Krilium) was marketed. The product was shown to improve physical properties and crop yields on certain soils. However, the application rate at which the benefits were found was not economical and interest in this polymer has declined.
Recently, new polymers applied at much lower rates have been promoted as soil conditioners. These polymers include natural polysaccharides, anionic and cationic polymers, and polyacrylamides. The compounds are long-chain, polymeric organic compounds that have a very high-molecular weight. Polymers bind particles together and form stable aggregates. Research is being conducted to identify polymer types as well as application methods and rates to maintain or improve the physical conditions of different soils. Results to date, under field conditions at low rates of application, have not shown consistent, significant improvement in a soil's physical condition.
Mineral Conditioners
Gypsum – has long been recognized for its benefits on high-sodium-containing soils. As mentioned above, gypsum is a mineral that occurs in nature as soft crystalline rock and varies in purity. Gypsum has been shown to displace exchangeable sodium from the cation exchange sites of soils high in sodium. On irrigated or dry land, gypsum can be used to reclaim saline areas or slick spots, soften and crumble alkali hard pans, supply calcium on low-exchange-capacity soils, and improve infiltration for some puddled soils. Gypsum is not recommended on soils containing native gypsum or areas irrigated with water containing abundant amounts of calcium and magnesium. The amount of gypsum to apply depends on the purity of the gypsum and the quantity of sodium present in the soil. Actual rates should be based on the results of a salt-alkali soil test.
Limestone – is crushed rock and other products high in calcium and/or magnesium that will improve the physical condition of some soils, when applied at several tons per acre. However, no consistent response for improving a soil's physical condition has been documented. Most of these products at the rates recommended will not supply enough calcium and/or magnesium to change the cation composition of the soil exchange complex. Several other categories of soil conditioners, including surfactants, such as ammonium alkyl ether sulfate, are claimed to improve soil physical properties, but researchers are still evaluating them.
Biostimulants and Growth Enhancement
Poor soil can restrict water intake into the tree and limit tree growth. Arborists, landscape architects, nurseries, and researchers are interested in improving the physical condition of the soil. These goals can be accomplished in part through the use of amending materials that improve the soil's physical condition.
Biostimulants
Biostimulants are living organisms or extracts from living things that can either help protect plants from disease or invigorate growth. They include powdered live forms of organic compounds such as mycorrhizal fungi, beneficial fungi (Gliocladium, Tricoderma), and root-colonizing bacteria (Streptomycetes, Bacillus, Pseudomonas). They also include such things as yucca extracts (wetting agent), kelp, humates, protein hydrolysates, and glutens that provide slow release forms of nitrogen. Certain harmful soil pests can be controlled with chili pepper spray, garlic tea, and Neem oil (a broad-spectrum insecticide derived from the oil of Neem tree (Azadirachta indica) seeds).
The term 'biostimulant' has been used to describe various substances involved in horticultural production over the past few decades. They were originally developed to promote root growth in agriculture and increased root crops by 20 – 30%. They also were used to reduce stress, disease susceptibility, and improve root quality. In recent years, however, it has been established that a biostimulant is a substance that is not a plant nutrient or pesticide but in some manner has a positive impact on soil and plant health. The biostimulant may enhance metabolism and respiration, increase chlorophyll efficiency and production, increase antioxidants, nucleic acid synthesis, enhance nutrient availability and increase the water holding capacity of the soil.
The benefits of biostimulants have been recognized for some time and university research has been published showing various benefits to growing organisms. In several research studies, biostimulants have decreased certain problems leading to chlorosis by enabling the plant to absorb minerals not readily available within the soil profile. University research has demonstrated the effectiveness of biostimulants and how they help retain a healthy forest soil environment. Also biostimulants have been shown to enable antioxidant activity in both the soil and within the plant, especially when the plants are under stress. In many cases, biostimulants help the tree recover quickly from stress and rejuvenate the root system.
In the age where caution has to be utilized with chemicals placed on the landscape, biostimulants can help by utilizing organic means of replenishing nutrients into the soil, while enabling the plant to uptake products more efficiently. At the same time, biostimulants decrease the overall amount of nitrate rich fertilizers, pesticides, and fungicides that need to be applied. The results of current research indicate that biostimulants can improve root growth after transplanting. However, the appropriate biostimulant must be used for the specific species, and many biostimulants do not meet the manufacturer's claims.
Advantages
Sea Kelp
This product is often used as a source of beneficial bacteria. However, sea kelp must be thoroughly washed to remove any salt residue and sea kelp extracts provide few plant hormones so the product effect is negligible.
Amino acids
Amino acids are the building blocks of protein. They take part in a tree's physiological processes that control photosynthetic activity and enhance water and nutrient efficiency of the plant. Plants save energy when treated with amino acids. In principle, the saved energy can be used for other processes resulting in a healthy and efficient plant that can withstand stress and the onslaught of disease.
Commercial Biostimulants
There are many products available that provide nutrients, organic substances, vitamins, amino acids, and enzymes that are advertised to improve plant vigor. However, research has not confirmed that all commercial products make a substantial difference. Furthermore, the biostimulants product industry is not regulated, nor is it subject to any quality control testing.
Poor soil can restrict water intake into the tree and limit tree growth. Arborists, landscape architects, nurseries, and researchers are interested in improving the physical condition of the soil. These goals can be accomplished in part through the use of amending materials that improve the soil's physical condition.
Biostimulants
Biostimulants are living organisms or extracts from living things that can either help protect plants from disease or invigorate growth. They include powdered live forms of organic compounds such as mycorrhizal fungi, beneficial fungi (Gliocladium, Tricoderma), and root-colonizing bacteria (Streptomycetes, Bacillus, Pseudomonas). They also include such things as yucca extracts (wetting agent), kelp, humates, protein hydrolysates, and glutens that provide slow release forms of nitrogen. Certain harmful soil pests can be controlled with chili pepper spray, garlic tea, and Neem oil (a broad-spectrum insecticide derived from the oil of Neem tree (Azadirachta indica) seeds).
The term 'biostimulant' has been used to describe various substances involved in horticultural production over the past few decades. They were originally developed to promote root growth in agriculture and increased root crops by 20 – 30%. They also were used to reduce stress, disease susceptibility, and improve root quality. In recent years, however, it has been established that a biostimulant is a substance that is not a plant nutrient or pesticide but in some manner has a positive impact on soil and plant health. The biostimulant may enhance metabolism and respiration, increase chlorophyll efficiency and production, increase antioxidants, nucleic acid synthesis, enhance nutrient availability and increase the water holding capacity of the soil.
The benefits of biostimulants have been recognized for some time and university research has been published showing various benefits to growing organisms. In several research studies, biostimulants have decreased certain problems leading to chlorosis by enabling the plant to absorb minerals not readily available within the soil profile. University research has demonstrated the effectiveness of biostimulants and how they help retain a healthy forest soil environment. Also biostimulants have been shown to enable antioxidant activity in both the soil and within the plant, especially when the plants are under stress. In many cases, biostimulants help the tree recover quickly from stress and rejuvenate the root system.
In the age where caution has to be utilized with chemicals placed on the landscape, biostimulants can help by utilizing organic means of replenishing nutrients into the soil, while enabling the plant to uptake products more efficiently. At the same time, biostimulants decrease the overall amount of nitrate rich fertilizers, pesticides, and fungicides that need to be applied. The results of current research indicate that biostimulants can improve root growth after transplanting. However, the appropriate biostimulant must be used for the specific species, and many biostimulants do not meet the manufacturer's claims.
Advantages
- Biostimulants will not kill insects, but they will help trees compartmentalize any damage quickly.
- Biostimulants will not cure any tree or shrub disease, but they will help improve a tree's disease resistance.
- Biostimulants will not add micro-nutrients to deficient soils or correct soil pH problems, but they will increase a soil amendment's effectiveness.
- Biostimulants have taken their rightful place as a catalyst for improving soil and the trees themselves.
- Biostimulants improve plant establishment and help produce healthier, stronger trees.
- Biostimulants promote beneficial microbial activity on new building sites where topsoil has been removed or compacted around existing trees.
- Biostimulants improve water and nutrient absorption in poor soils by promoting beneficial microbial activity and mycorrhizae development.
- Biostimulants help protect against soil borne pathogens and enhance soil health.
- Biostimulants help to break down herbicide or salt build-up in soil.
- Biostimulants encourage mycorrhizae development in urban soils with little organic content.
- Biostimulants improve effectiveness of soil amendment treatments and fertilization applications.
- Biostimulants benefit trees by improving feeder root development and the absorption of water and nutrients.
- Biostimulants protect trees against soil disease, while improving tree longevity, survival, and while also
increasing survival rates of transplanted trees. These stimulants help to reduce damage from drought stress and provide a healthier appearance and growth to trees.
Sea Kelp
This product is often used as a source of beneficial bacteria. However, sea kelp must be thoroughly washed to remove any salt residue and sea kelp extracts provide few plant hormones so the product effect is negligible.
Amino acids
Amino acids are the building blocks of protein. They take part in a tree's physiological processes that control photosynthetic activity and enhance water and nutrient efficiency of the plant. Plants save energy when treated with amino acids. In principle, the saved energy can be used for other processes resulting in a healthy and efficient plant that can withstand stress and the onslaught of disease.
Commercial Biostimulants
There are many products available that provide nutrients, organic substances, vitamins, amino acids, and enzymes that are advertised to improve plant vigor. However, research has not confirmed that all commercial products make a substantial difference. Furthermore, the biostimulants product industry is not regulated, nor is it subject to any quality control testing.
Surfactants, Antitranspirants, Water Absorbing Gels
Arborists, nurseries, and researchers alike are interested in improving the physical condition of the soil to enhance tree growth. These goals can be accomplished in part through the use of good management techniques and amending materials that improve the soil's physical condition.
Surfactants
Commercial surfactants (wetting agents) are employed to improve water penetration, especially when watering trees or when applying soluble fertilizers by spray, drenching, or soil injections. Soil surfactants were introduced to the nursery industry more than 50 years ago. They improve water penetration and water distribution in areas exhibiting stress caused by water repellency, in other words, they make water wetter. Soil water repellency manifests itself in a variety of ways, most obviously in the reduction of infiltration rates of water. University research suggests that a main source of water repellency (hydrophobicity) is the development of an organic coating on soil or sand particles. Water repellency can develop in varying degrees, at any time. While there appears to be several causes of the organic coating, including microorganisms and fungal hyphae, one of the primary causes of water repellency is simply a consequence of the breakdown of organic substances, a natural process that occurs in all soils. Whatever the cause or the soil type it affects, these coatings eventually interfere with water movement in soils and can lead to drought stress.
When the organic coating becomes dry, water is repelled. Irrigation practices that encourage wetting and drying cycles may actually accentuate the development and degree of water repellency. It appears that this water-repellent organic coating cannot be removed from the soil particles unless extreme, potentially damaging measures are taken. However, there are ways to manage water repellency and reduce the symptoms. The best strategy seems to be a combination of good management practices along with the use of a soil surfactant.
A soil surfactant molecule is made up of a hydrophilic ("water loving") and a hydrophobic ("water hating") end. Hydrophobic components are attracted to each other. Therefore the hydrophobic end of the surfactant molecule attaches to the hydrophobic organic coating of the soil particle. This leaves the hydrophilic end of the surfactant molecule facing outward, providing a site for water to attach, and thus allowing the soil particle to become hydrated. This has a positive impact on penetration and the distribution of water, fertilizer, and other chemicals that are dispersed into the soil by water.
However, not all surfactants are the same; molecular constructions can differ in weight, shape, and size. Any of these variations can significantly influence the effectiveness of the soil surfactant. Arborists should select a soil surfactant based on their particular needs, desired hydration requirements, and tree management strategy.
Adding a surfactant requires using a reliable pump that will inject a soil surfactant directly into the irrigation water. Implementing this program should increase water infiltration and an overall healthy appearance of the soil and the tree. An effective surfactant will combat the detrimental effects of trees under stress caused by water repellency.
Recent research by the Golf Course Superintendents Association of America looked at several wetting agents. The results were mixed. None of the wetting agent treatments significantly improved turfgrass color or quality during the trials. However, the researchers did find that all the products reduced hydrophobicity compared with no treatment at all.
Localized dry spots are most severe during periods of extended high temperatures and dry weather. Recommended treatments for managing dry spots include:
Antitranspirants
Antitranspirants are chemicals capable of reducing the transpiration rate when applied to a tree's leaves. Since water loss normally occurs through the stomata pores in the leaves, antitranspirants are usually foliar sprays, although they may sometimes be used more conveniently as dips for immersing the above ground plant parts. The idea of coating plant foliage with waxy materials to curtail transpiration, particularly for transplanted seedlings, is not new, but research in this field is relatively recent.
Foliar sprays may reduce transpiration in three different ways:
Pros & Cons of Antitranspirants
The scientific literature on antitranspirants is robust and conflicting. For example, according to recent research:
The bottom line is that antitranspirants prevent stomatal water loss and increase heat load, inhibit gas exchange, and decrease photosynthesis.
Instead of using antitranspirants, consider choosing site-appropriate plants; know the water needs of selected species, and install accordingly. Species with large thin leaves are more sensitive to water stress than those with small thick leaves or needles. A little water stress is a good thing because it will help acclimate the plant to future drought. There is no substitute for adequate soil water, so maintain adequate soil moisture in newly installed landscapes through mulching and other sustainable practices. Maintain optimal soil temperatures through mulching because cooler soils have less evaporation.
Water Absorbing Gels
The water needs of trees and shrubs vary throughout the growing season. A consistent, readily available source of nutrients and water is essential for proper plant growth. Moisture crystals or hydrogels act as a time-release water polymer gel that absorbs and stores many times their weight in water and release it to plants on demand. When added to the soil, moisture crystals reduce plant shock and the effects of drought. This will reduce the amount and frequency of watering as well as reducing plant losses due to water stress.
When added to the soil, moisture crystals can absorb water in the amount of approximately 200 times its dry weight. The plant roots grow directly into the water-swollen polymers, tapping the reserve when needed. Moisture crystals work quickly and absorb most of their capacity in two to three hours; 95% of the water absorbed is available to the plant.
According to one manufacturer, once applied to the soil, moisture crystals remain an effective water management tool for at least 2 years. Moisture crystals also absorb, hold, and release soluble fertilizers. They are environmentally friendly and non-toxic. With an essentially neutral pH, moisture crystals eventually break down in the soil into its component parts of ammonia, carbon dioxide, and water and is less toxic than table salt.
During the installation process, B&B material can lose up to 95% of the root system. With such a small amount of roots left, moisture crystals make sense. They will absorb water and keep it near the developing roots to provide a critical element of support for newly installed trees or shrubs.
Plant materials from containers are water-critical. Although a containerized tree retains its total root system, its water needs double after the container is removed and the tree begins to establish itself in its new landscape environment. This is because of the loss of its perched water table. When soil is in a container, it remains saturated at the bottom of the container after irrigation. The equilibrium of downward gravitational pull and the attraction of water adhering to soil particles create a saturation zone condition. This water is available to the plant while it is containerized. Once the container is removed and the plant is set into the ground, this saturation zone condition no longer exists. Water moves freely downward and largely away from the plant's ability to access it.
Commercial products are available in a variety of particle sizes. For example:
1. The root dip product is very small so it will cling to bare roots.
2. The soil amendment product for tree installation is a little coarser.
3. The broadcast and soil mix sizes are a little larger.
4. The potting mix is the largest particle size product.
Arborists, nurseries, and researchers alike are interested in improving the physical condition of the soil to enhance tree growth. These goals can be accomplished in part through the use of good management techniques and amending materials that improve the soil's physical condition.
Surfactants
Commercial surfactants (wetting agents) are employed to improve water penetration, especially when watering trees or when applying soluble fertilizers by spray, drenching, or soil injections. Soil surfactants were introduced to the nursery industry more than 50 years ago. They improve water penetration and water distribution in areas exhibiting stress caused by water repellency, in other words, they make water wetter. Soil water repellency manifests itself in a variety of ways, most obviously in the reduction of infiltration rates of water. University research suggests that a main source of water repellency (hydrophobicity) is the development of an organic coating on soil or sand particles. Water repellency can develop in varying degrees, at any time. While there appears to be several causes of the organic coating, including microorganisms and fungal hyphae, one of the primary causes of water repellency is simply a consequence of the breakdown of organic substances, a natural process that occurs in all soils. Whatever the cause or the soil type it affects, these coatings eventually interfere with water movement in soils and can lead to drought stress.
When the organic coating becomes dry, water is repelled. Irrigation practices that encourage wetting and drying cycles may actually accentuate the development and degree of water repellency. It appears that this water-repellent organic coating cannot be removed from the soil particles unless extreme, potentially damaging measures are taken. However, there are ways to manage water repellency and reduce the symptoms. The best strategy seems to be a combination of good management practices along with the use of a soil surfactant.
A soil surfactant molecule is made up of a hydrophilic ("water loving") and a hydrophobic ("water hating") end. Hydrophobic components are attracted to each other. Therefore the hydrophobic end of the surfactant molecule attaches to the hydrophobic organic coating of the soil particle. This leaves the hydrophilic end of the surfactant molecule facing outward, providing a site for water to attach, and thus allowing the soil particle to become hydrated. This has a positive impact on penetration and the distribution of water, fertilizer, and other chemicals that are dispersed into the soil by water.
However, not all surfactants are the same; molecular constructions can differ in weight, shape, and size. Any of these variations can significantly influence the effectiveness of the soil surfactant. Arborists should select a soil surfactant based on their particular needs, desired hydration requirements, and tree management strategy.
Adding a surfactant requires using a reliable pump that will inject a soil surfactant directly into the irrigation water. Implementing this program should increase water infiltration and an overall healthy appearance of the soil and the tree. An effective surfactant will combat the detrimental effects of trees under stress caused by water repellency.
Recent research by the Golf Course Superintendents Association of America looked at several wetting agents. The results were mixed. None of the wetting agent treatments significantly improved turfgrass color or quality during the trials. However, the researchers did find that all the products reduced hydrophobicity compared with no treatment at all.
Localized dry spots are most severe during periods of extended high temperatures and dry weather. Recommended treatments for managing dry spots include:
- cultivation of localized dry spots to increase water penetration,
- hand watering to increase soil moisture content,
- preventive and/or curative application of wetting agents.
Antitranspirants
Antitranspirants are chemicals capable of reducing the transpiration rate when applied to a tree's leaves. Since water loss normally occurs through the stomata pores in the leaves, antitranspirants are usually foliar sprays, although they may sometimes be used more conveniently as dips for immersing the above ground plant parts. The idea of coating plant foliage with waxy materials to curtail transpiration, particularly for transplanted seedlings, is not new, but research in this field is relatively recent.
Foliar sprays may reduce transpiration in three different ways:
- Reflecting materials reduce the absorption of radiant energy and thereby reduce leaf temperatures and transpiration rates;
- Emulsions of wax, latex, or plastics, dry on the foliage to form thin transparent films which hinder the
escape of water vapor from the leaves; - Certain chemical compounds can prevent stomata from opening fully (by affecting the guard cells around the stomata pores), thus decreasing the loss of water vapor from the leaf. However, such coatings may curtail photosynthesis on overcast days when light is limited.
Pros & Cons of Antitranspirants
The scientific literature on antitranspirants is robust and conflicting. For example, according to recent research:
- Disease control: Antitranspirants decreased or had no effect on bacterial and fungal diseases; other research indicated it helped reduce insect pests.
- Fruit production: Antitranspirants increased, decreased, or did not affect fruit splitting; decreased or did not affect marketable yield; and increased water loss from fruit.
- Heat or cold-induced desiccation: Antitranspirants had no effect.
- Root production: Antitranspirants delayed or had no effect on growth of cuttings; other research indicated it increased the accumulation of calcium in roots.
- Installation stress: Antitranspirants increased, decreased, or had no effect on plant survival; increased, decreased, or had no effect on transpiration; increased, decreased, or had no effect on leaf water content; reduced the growth rate; decreased the height; increased or decreased fresh and dry weight; delayed leaf unfolding; increased leaf drop; had no effect on root regeneration; decreased evaporative cooling and increased leaf temperature; depressed chlorophyll content.
- Weed Control: Antitranspirants decreased transpiration, increased leaf temperature, and thereby increased weed mortality.
The bottom line is that antitranspirants prevent stomatal water loss and increase heat load, inhibit gas exchange, and decrease photosynthesis.
Instead of using antitranspirants, consider choosing site-appropriate plants; know the water needs of selected species, and install accordingly. Species with large thin leaves are more sensitive to water stress than those with small thick leaves or needles. A little water stress is a good thing because it will help acclimate the plant to future drought. There is no substitute for adequate soil water, so maintain adequate soil moisture in newly installed landscapes through mulching and other sustainable practices. Maintain optimal soil temperatures through mulching because cooler soils have less evaporation.
Water Absorbing Gels
The water needs of trees and shrubs vary throughout the growing season. A consistent, readily available source of nutrients and water is essential for proper plant growth. Moisture crystals or hydrogels act as a time-release water polymer gel that absorbs and stores many times their weight in water and release it to plants on demand. When added to the soil, moisture crystals reduce plant shock and the effects of drought. This will reduce the amount and frequency of watering as well as reducing plant losses due to water stress.
When added to the soil, moisture crystals can absorb water in the amount of approximately 200 times its dry weight. The plant roots grow directly into the water-swollen polymers, tapping the reserve when needed. Moisture crystals work quickly and absorb most of their capacity in two to three hours; 95% of the water absorbed is available to the plant.
According to one manufacturer, once applied to the soil, moisture crystals remain an effective water management tool for at least 2 years. Moisture crystals also absorb, hold, and release soluble fertilizers. They are environmentally friendly and non-toxic. With an essentially neutral pH, moisture crystals eventually break down in the soil into its component parts of ammonia, carbon dioxide, and water and is less toxic than table salt.
During the installation process, B&B material can lose up to 95% of the root system. With such a small amount of roots left, moisture crystals make sense. They will absorb water and keep it near the developing roots to provide a critical element of support for newly installed trees or shrubs.
Plant materials from containers are water-critical. Although a containerized tree retains its total root system, its water needs double after the container is removed and the tree begins to establish itself in its new landscape environment. This is because of the loss of its perched water table. When soil is in a container, it remains saturated at the bottom of the container after irrigation. The equilibrium of downward gravitational pull and the attraction of water adhering to soil particles create a saturation zone condition. This water is available to the plant while it is containerized. Once the container is removed and the plant is set into the ground, this saturation zone condition no longer exists. Water moves freely downward and largely away from the plant's ability to access it.
Commercial products are available in a variety of particle sizes. For example:
1. The root dip product is very small so it will cling to bare roots.
2. The soil amendment product for tree installation is a little coarser.
3. The broadcast and soil mix sizes are a little larger.
4. The potting mix is the largest particle size product.
Tree Growth Regulators
Types of Tree Growth Regulators (TGR):
1) Type One TGR was invented in the 1950s. These regulators stop cell division on contact. Many of the herbicides used today are made from these materials. Type One TGR’s can be very effective for preventing unwanted sucker sprouts. If applied systemically, they will cause disfigurement, and so they are best applied through aerosol sprays.
2) Type Two TGR was developed about 30 years ago and works quite different. Instead of inhibiting cell division, Type Two inhibit cell enlargement. The cells remain wholly intact, except for their size. The number of cells produced by the tree also remains the same.
Paclobutrazol (PBZ) Type Two TGR
Arborists know this product as Cambistat®. A Type 2 TGR is a chemical that suppresses the production of gibberelin, the plant hormone that is responsible for cell elongation in the growing tips of trees and cause them to generate more chlorophyll and increased levels of Abscissic acid. The effect of the additional chlorophyll is greener leaves. Higher levels of the abscissic acid are believed to be responsible for the increased root growth, thicker leaves and the increased drought tolerance exhibited in the treated trees.
Paclobutrazol features include:
Reducing growth with PBZ reduces the amount of energy spent on shoot growth and may stimulate fine root development. There are theories as to why these growth retardants give plants protection from drought. One theory is that the thicker leaf has more water holding capacity, and more roots can gather and store more water. Thicker leaves have a smaller percentage of exposed tissue than thinner leaves, and because treated leaves have a lot more trichome hairs covering the stomata, there may be a physical obstruction to water loss.
Cambistat®
Cambistat® is a soil-applied TGR that is currently being used in the arboricultural industry to reduce tree growth 40% to 60% over a three year period and provide pre-stress conditioning therapy for trees in stressful sites. Studies have demonstrated that Cambistat® enhances rooting, increases tree tolerance to drought, and reduces the incidence of certain diseases. Treated trees have a growth reduction, thus trimming cycles can be extended significantly and a lot of money is saved.
Cambistat® is best applied to the tree at the soil / trunk interface. This can be done with a drench poured into a 2 – 4” deep trench at the base of the tree. Another method of application is by injection into the soil right next to the tree. The roots of the tree will absorb the chemical and disperse it through the tree’s crown to suppress the subsequent growth of the tree. There is no injury to the tree from a TGR application. Every species of tree that has been studied to date has been assigned a letter on the rate chart that signifies the dose of Cambistat® that is needed to give it the right amount of growth control. There are 6 categories – A to F. Too much PBZ on sensitive trees can result in too much growth control. While this will not harm the tree, it can result in a tree that may not be very pleasing to the eye. When the Cambistat label instructions are followed, this should not be an issue.
Effects
The effect of a TGR application will take several months or longer to become apparent. The first effect that will be noticed is an enhanced greening of the leaf. This is caused by the fact that PBZ actually stimulates the tree to produce more chlorophyll. The growth reduction of the tree can take longer, and often becomes apparent the season following application. The crown of a treated tree is typically more dense and compact than an untreated tree.
Risks
It is very important to utilize the application guide and rate chart that comes with the PBZ product to make sure it is updated with information coming from companies using the material. It must be applied correctly – too much PBZ or poor application technique can make a tree grow too slowly. This results in small leaves and the "poodle" effect. The tree will not die and it will eventually grow out of this condition, but people can become alarmed and upset when this happens.
Benefits of Slow Growth
It all comes down to energy allocation. Slowing down the growth of a tree conserves energy. Less energy is spent on top growth, which means more is available for reserves, roots, defense, etc. One of the myths that people have about trees is that fast growth is a sign of health. Health from a tree's perspective is more related to energy than growth. Slower growing trees tend to have higher levels of energy than faster growing trees of the same species. Bigger trees require more energy to maintain.
Tree Characteristic Tree Growth Rate Comparison
___________________________Faster Growth Slower Growth
Resource Demand higher lower
Sensitivity to Resource Availability higher lower
Stored Energy Reserves lower higher
Root/Shoot Ratio lower higher
Sensitivity to Stress or Damage more sensitive less sensitive
Overall Tree Durability less durable more durable
Urban Trees
Urban trees are surrounded by underground obstacles that prevent their root systems from becoming as large as the tree would usually have in unconstrained locations. Add to this the problem of poor quality soil (compaction, low organic matter, herbicides, and few nutrients) and it becomes clear why urban tree lifespans are so greatly limited. A tree's lifespan is not determined by a biological clock but by its ability to make enough energy to support its living mass. Once they reach a "critical size," they become too large to be supported by the environment in which they live. They then begin to decline.
Residential yard soils also have a poor capacity to support tree roots. Turf is so competitive that tree roots in lawns are literally half as abundant as in the forest. This limits how large a tree can get before it will start to decline. Research has shown that laying down a 3-inch layer of mulch under the tree's canopy and removing the turf will double the root system in that area. A healthier soil will increase the capacity of the site to support a larger and healthier tree. The tree will also be able to grow significantly more roots.
There are many reasons why a tree may show symptoms of decline, including soil compaction, irrigation and drainage problems, herbicide damage, grade changes, etc. If the cause of the decline is not addressed, then treatment with a TGR is unlikely to have the desired effect. A TGR should be used in conjunction with other arboricultural practices such as radial trenching, vertical mulching, fertilization to correct mineral deficiencies, etc.
Leaf Disease Impacts
A number of studies have shown that PBZ can have a positive impact on preventing disease infection of the leaves. While the exact mode of this protection is not known, there are two theories that may explain this.
1) The first theory is that the morphological changes of the leaves of treated trees (thicker, more trichome hairs, more chlorophyll) change the disease - leaf interaction. Many tree diseases are highly specific to certain kinds of trees, so by changing the leaf morphology there may be a lack of "recognition" or susceptibility of that leaf to the disease that use to infect it.
2) A second theory is that the increase in trichome hairs creates a physical barrier to disease infection. To understand this, first understand how leaves catch fungal infections. Basically, a fungal spore comes through the air and lands on the leaf. When it gets moisture and the temperature is right, it hatches and a little tentacle (mycelia) comes out and grows in an attempt to get into the leaf before the moisture disappears. If the moisture is present long enough and the fungus is successful, it creates a more difficult journey for the mycelia. PBZ doesn't prevent infection, but it can delay significantly the time needed for an infection to develop.
3) In one recent study from the University of Lancaster in the United Kingdom, researchers tested the ability of nine tree species to capture air pollution dusts in wind-tunnel experiments. Silver birch (Betula pendula), yew (Taxus sp.) and boxelder trees (Acer negundo) were the most effective at capturing industrial dust particles, with the hairs of their leaves contributing to reduction rates of 79%, 71% and 70% respectively. Conifers, like pines and cypresses, are also good natural purifiers.
Bacterial Leaf Scorch
Bacterial leaf scorch (BLS), caused by Xylella fastidiosa, is a destructive disease that affects a number of economically important tree species in the eastern, southern, and mid-west United States. Quercus, Ulmus, Platanus, Acer, Nyssa, and Morus are among the tree species that this disease affects. Symptoms can first be noticed in early summer, but usually increase and intensify throughout the growing season and can be more pronounced in moisture limiting conditions. Most trees with BLS usually display decreased vigor and slowly decline over a number of years.
Bartlett Tree Research Laboratories has been conducting ongoing research on the use of PBZ for suppression of BLS with very promising results. The study showed that PBZ suppressed the decline associated with this disease in five different trees. This disease application needs additional research, but it is interesting to note that the treatment has no impact on the bacteria itself. It is speculated that by changing the morphology of leaves and making them more drought tolerant, the bacteria's effect of dehydrating the tree is reduced.
Note: The mention of product names in this Topic does not constitute an endorsement of these in particular. They are mentioned only for providing the reader with useful information.
Sources
The test that follows contains 80 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test.
ISA will award 4.0 CEUs* for a passing grade. SAF members will earn 1.0 Cat. 1-CT credit for a passing grade. The cost for taking this test is $20 per credit. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Tests with passing scores may be submitted only once to each organization.
*Members of ISA may apply the 4.0 CEUs toward Certified Arborist, Tree Worker Specialist, Utility Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to Merchant' / gibneyCE.com. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks* after that. ISA maintains a record of CEU credits on their website *SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the 'sending your answers' response.
Types of Tree Growth Regulators (TGR):
1) Type One TGR was invented in the 1950s. These regulators stop cell division on contact. Many of the herbicides used today are made from these materials. Type One TGR’s can be very effective for preventing unwanted sucker sprouts. If applied systemically, they will cause disfigurement, and so they are best applied through aerosol sprays.
2) Type Two TGR was developed about 30 years ago and works quite different. Instead of inhibiting cell division, Type Two inhibit cell enlargement. The cells remain wholly intact, except for their size. The number of cells produced by the tree also remains the same.
Paclobutrazol (PBZ) Type Two TGR
Arborists know this product as Cambistat®. A Type 2 TGR is a chemical that suppresses the production of gibberelin, the plant hormone that is responsible for cell elongation in the growing tips of trees and cause them to generate more chlorophyll and increased levels of Abscissic acid. The effect of the additional chlorophyll is greener leaves. Higher levels of the abscissic acid are believed to be responsible for the increased root growth, thicker leaves and the increased drought tolerance exhibited in the treated trees.
Paclobutrazol features include:
- PBZ applications significantly slow the growth of a tree, but do not eliminate growth or the need for tree pruning.
- The application of PBZ will reduce the growth of the tree by 30 – 80%, depending upon the species of tree and the application rate.
- PBZ applications will simply extend the trim cycle intervals between prunings and reduce the amount of pruning needed.
- The use of a PBZ on trees directly under power lines will enable utilities to maintain their systems on a
longer pruning cycle with minimal encroachment of branches that could cause an outage. - PBZ use has been shown to alter the allocation of resources from the production of leaves to favor root growth and the production of defensive chemicals. This may increase the tree’s ability to survive insect and disease attacks and to withstand environmental stresses like pollution and drought.
- PBZ has also been used to stimulate root regeneration after installation.
- It has been studied for the purpose of stabilizing declining trees that have insufficient fine root development. Treatment should be part of a complete tree care program that includes mulching.
- Laboratory and field evaluations over the past 30 years have shown that PBZ does not get into groundwater. The chemical is tightly bound to soil particles and only trace amounts of the chemical have been identified in the soil below 16 inches, even after months of heavy rain.
- The leaves and wood chips from trees treated with PBZ can be used for mulch without adverse impact on other plants.
Reducing growth with PBZ reduces the amount of energy spent on shoot growth and may stimulate fine root development. There are theories as to why these growth retardants give plants protection from drought. One theory is that the thicker leaf has more water holding capacity, and more roots can gather and store more water. Thicker leaves have a smaller percentage of exposed tissue than thinner leaves, and because treated leaves have a lot more trichome hairs covering the stomata, there may be a physical obstruction to water loss.
Cambistat®
Cambistat® is a soil-applied TGR that is currently being used in the arboricultural industry to reduce tree growth 40% to 60% over a three year period and provide pre-stress conditioning therapy for trees in stressful sites. Studies have demonstrated that Cambistat® enhances rooting, increases tree tolerance to drought, and reduces the incidence of certain diseases. Treated trees have a growth reduction, thus trimming cycles can be extended significantly and a lot of money is saved.
Cambistat® is best applied to the tree at the soil / trunk interface. This can be done with a drench poured into a 2 – 4” deep trench at the base of the tree. Another method of application is by injection into the soil right next to the tree. The roots of the tree will absorb the chemical and disperse it through the tree’s crown to suppress the subsequent growth of the tree. There is no injury to the tree from a TGR application. Every species of tree that has been studied to date has been assigned a letter on the rate chart that signifies the dose of Cambistat® that is needed to give it the right amount of growth control. There are 6 categories – A to F. Too much PBZ on sensitive trees can result in too much growth control. While this will not harm the tree, it can result in a tree that may not be very pleasing to the eye. When the Cambistat label instructions are followed, this should not be an issue.
Effects
The effect of a TGR application will take several months or longer to become apparent. The first effect that will be noticed is an enhanced greening of the leaf. This is caused by the fact that PBZ actually stimulates the tree to produce more chlorophyll. The growth reduction of the tree can take longer, and often becomes apparent the season following application. The crown of a treated tree is typically more dense and compact than an untreated tree.
Risks
It is very important to utilize the application guide and rate chart that comes with the PBZ product to make sure it is updated with information coming from companies using the material. It must be applied correctly – too much PBZ or poor application technique can make a tree grow too slowly. This results in small leaves and the "poodle" effect. The tree will not die and it will eventually grow out of this condition, but people can become alarmed and upset when this happens.
Benefits of Slow Growth
It all comes down to energy allocation. Slowing down the growth of a tree conserves energy. Less energy is spent on top growth, which means more is available for reserves, roots, defense, etc. One of the myths that people have about trees is that fast growth is a sign of health. Health from a tree's perspective is more related to energy than growth. Slower growing trees tend to have higher levels of energy than faster growing trees of the same species. Bigger trees require more energy to maintain.
Tree Characteristic Tree Growth Rate Comparison
___________________________Faster Growth Slower Growth
Resource Demand higher lower
Sensitivity to Resource Availability higher lower
Stored Energy Reserves lower higher
Root/Shoot Ratio lower higher
Sensitivity to Stress or Damage more sensitive less sensitive
Overall Tree Durability less durable more durable
Urban Trees
Urban trees are surrounded by underground obstacles that prevent their root systems from becoming as large as the tree would usually have in unconstrained locations. Add to this the problem of poor quality soil (compaction, low organic matter, herbicides, and few nutrients) and it becomes clear why urban tree lifespans are so greatly limited. A tree's lifespan is not determined by a biological clock but by its ability to make enough energy to support its living mass. Once they reach a "critical size," they become too large to be supported by the environment in which they live. They then begin to decline.
Residential yard soils also have a poor capacity to support tree roots. Turf is so competitive that tree roots in lawns are literally half as abundant as in the forest. This limits how large a tree can get before it will start to decline. Research has shown that laying down a 3-inch layer of mulch under the tree's canopy and removing the turf will double the root system in that area. A healthier soil will increase the capacity of the site to support a larger and healthier tree. The tree will also be able to grow significantly more roots.
There are many reasons why a tree may show symptoms of decline, including soil compaction, irrigation and drainage problems, herbicide damage, grade changes, etc. If the cause of the decline is not addressed, then treatment with a TGR is unlikely to have the desired effect. A TGR should be used in conjunction with other arboricultural practices such as radial trenching, vertical mulching, fertilization to correct mineral deficiencies, etc.
Leaf Disease Impacts
A number of studies have shown that PBZ can have a positive impact on preventing disease infection of the leaves. While the exact mode of this protection is not known, there are two theories that may explain this.
1) The first theory is that the morphological changes of the leaves of treated trees (thicker, more trichome hairs, more chlorophyll) change the disease - leaf interaction. Many tree diseases are highly specific to certain kinds of trees, so by changing the leaf morphology there may be a lack of "recognition" or susceptibility of that leaf to the disease that use to infect it.
2) A second theory is that the increase in trichome hairs creates a physical barrier to disease infection. To understand this, first understand how leaves catch fungal infections. Basically, a fungal spore comes through the air and lands on the leaf. When it gets moisture and the temperature is right, it hatches and a little tentacle (mycelia) comes out and grows in an attempt to get into the leaf before the moisture disappears. If the moisture is present long enough and the fungus is successful, it creates a more difficult journey for the mycelia. PBZ doesn't prevent infection, but it can delay significantly the time needed for an infection to develop.
3) In one recent study from the University of Lancaster in the United Kingdom, researchers tested the ability of nine tree species to capture air pollution dusts in wind-tunnel experiments. Silver birch (Betula pendula), yew (Taxus sp.) and boxelder trees (Acer negundo) were the most effective at capturing industrial dust particles, with the hairs of their leaves contributing to reduction rates of 79%, 71% and 70% respectively. Conifers, like pines and cypresses, are also good natural purifiers.
Bacterial Leaf Scorch
Bacterial leaf scorch (BLS), caused by Xylella fastidiosa, is a destructive disease that affects a number of economically important tree species in the eastern, southern, and mid-west United States. Quercus, Ulmus, Platanus, Acer, Nyssa, and Morus are among the tree species that this disease affects. Symptoms can first be noticed in early summer, but usually increase and intensify throughout the growing season and can be more pronounced in moisture limiting conditions. Most trees with BLS usually display decreased vigor and slowly decline over a number of years.
Bartlett Tree Research Laboratories has been conducting ongoing research on the use of PBZ for suppression of BLS with very promising results. The study showed that PBZ suppressed the decline associated with this disease in five different trees. This disease application needs additional research, but it is interesting to note that the treatment has no impact on the bacteria itself. It is speculated that by changing the morphology of leaves and making them more drought tolerant, the bacteria's effect of dehydrating the tree is reduced.
Note: The mention of product names in this Topic does not constitute an endorsement of these in particular. They are mentioned only for providing the reader with useful information.
Sources
- "Basics of Fertilizers", City Trees, The Journal of The Society of Municipal Arborists Vol. 37, Number 3 May/June 2001.
- Chalker-Scott, Dr. Linda, "Phosphorous", WNLA’s B&B newsletter, September 2000.
- Chalker-Scott, Linda, "The Myth of Antitranspirants", Issue 7, Center for Urban Horticulture, University of Washington, June 1999.
- Coder, Dr. Kim D. "Tree Root Growth Requirements", City Trees, The Journal of The Society of Municipal Arborists Vol. 38, Number 2 March/April 2002.
- Davenport, D. C., R. M. Hagan and P. E. Martin, "Antitranspirants Uses and Effects On Plant Life", California Turfgrass Culture, vol. 19 no.4.
- Dong, S., L. Cheng, C. Scagel, and L. Fuchigami, "Nitrogen Absorption, Translocation, and Distribution", Tree Physiology, 2002.
- Durden, Carol, "Fertilizer Label", Minnesota Department of Agriculture, September 5, 2008.
- Elliott, Marianne and Robert L. Edmonds, "Soil Nitrogen and Disease Severity in Pacific Madrone Habitats", Center for Urban Horticulture, University of Washington, Autumn 2001.
- "Fertilizers for the Garden", City Trees, Vol. 37, Number 4 July/August 2001.
- Foerster, Vic, "Biostimulants", ArborAge, April 2003.
- Gillman, Jeff and Carl Rosen, "Tree Fertilization", FO-07410, University of Minnesota, Department of
Horticulture, 2000. - Gilman, Edward E. et. al., "Fertilizer Impact In Sandy Soil", Journal of Arboriculture 26(3): 177-18
- "Guide to Arbor Care", Plant Health Care, Inc. 2011.
- Hickman, John S. and David A. Whitney, "Soil Conditioners", Publication # 295, North Central Regional Extension.
- Jackson, William R. PhD, "Humic, Fulvic and Microbial Balance: Organic Soil Conditioning", Jackson Research Center, Evergreen, CO, 1993.
- Kernan, Michael J. PhD, "Biological Treatments for City Trees", City Trees, Vol. 40, Number 3 May/June 2004.
- Lantagne, Douglas, "Increasing Hardwood Planting Success Using Tree Shelters", Forestry Fact Sheet 12, University of Michigan, September, 1989.
- Mathers, Dr. Hannah, "Field Planting of Caliper Trees", Nursery News, Vol. 20 No. 7, July 2005.
- Nesmith, J. and E.W. McElwee, Circular 352, Florida Cooperative Extension Service, 2010.
- Organic Gardening staff, "Testing for 5 Key Compost Characteristics", Organic Gardening Magazine, 1992.
- Percival, Glynn C., "Are Biostimulants the Next Generation of Fertilizer?", Tree Care Industry, March 2004.
- Perry, Leonard, "pH for the Garden", University of Vermont Extension, 2003.
- Phillips, Leonard, "Using Moisture Crystals", City Trees, Vol. 38 No. 2, pg. 9, May/June 2002.
- Robbins, Jim, "Fertilizer Facts", Nursery Management and Production, P. 30 - 33, October 2003.
- Schmidt, R. E., PhD, Zhang, Zunzhong, PhD, "How Humic Substances Help Turfgrass Grow" Golf Course Management, July 1998.
- "Selecting a Surfactant Strategy", Turfnotes, November 2003.
- Shinano T., M Osaki, and M. Kato, "Differences In Nitrogen Of Trees", Tree Physiology 21:712-624
- Struve, Daniel K., "Nitrogen Research in the US", Journal of Arboriculture, Vol. 28, No. 6 November 2002.
- Trowbridge, Peter J. and Nina L. Bassuk, Trees in the Urban Landscape, John Wiley & Sons, Inc.
2004.
The test that follows contains 80 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test.
ISA will award 4.0 CEUs* for a passing grade. SAF members will earn 1.0 Cat. 1-CT credit for a passing grade. The cost for taking this test is $20 per credit. If you purchase an annual subscription for 15 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report all passing test scores to ISA and/or SAF. If you are a member of ISA and SAF we will report your passing test scores to both for no additional cost. Tests with passing scores may be submitted only once to each organization.
*Members of ISA may apply the 4.0 CEUs toward Certified Arborist, Tree Worker Specialist, Utility Specialist, Municipal Specialist, Aerial Lift Specialist, or BCMA science credits.
California UFC members will receive credit for passing the test. Please add your CaUFC number after your ISA and/or SAF certification number.
ASCA and MTOA members may submit your ISA certification record to these organizations and receive credits one for one.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment online securely with your credit card or Pay Pal account. After your payment is submitted, click on ‘Return to Merchant' / gibneyCE.com. That will take you to the test sign in page followed by the test. Members with certifications from both ISA and SAF, please be sure to add both of your certification numbers. These numbers are important for reporting purposes.
To take the test as an annual subscriber with reduced rates, click on Password and enter your test password which will take you to the test sign in page. If you would like to become a subscriber see our Annual Subscription page for details.
When you have finished answering all questions you will be prompted to click ‘next’ to send your answers to gibneyCE.com. You can then click ‘next’ to view your test summary. A test review of your answers is available upon request.
All passing test scores are sent from gibneyCE.com to your organization(s) at the end of every month and they will appear on your certification record 4 to 6 weeks* after that. ISA maintains a record of CEU credits on their website *SAF requires 5 passing test scores before reporting.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option. You can spend as much time as you would like to take the test but it is important not to leave the test site until you have answered all the questions and see the 'sending your answers' response.