LA Course #GCE-1-1903
Sustainability Issues 3 - Roots, Soil and Mulch
Sections Go directly to the Section by clicking on the title below
Sustainability Issues 3 - Roots, Soil and Mulch
Sections Go directly to the Section by clicking on the title below
Note: Click on green text in each section for more information and photos.
Critical Root Zones for Trees
by Len Phillips
Note: See 6 credit course ‘Trees on Building Sites’ for an expanded version for this article.
Field investigation and research in the last two decades have destroyed the myth that the root system extends only to the drip line of a tree's canopy. Another false myth is that all mature trees have a taproot that is the most vulnerable portion of the root system. Another perspective that dry climate trees have similar root systems to trees growing in climates that receive abundant rainfall during the growing season has to be re-considered. The trees growing in areas that do not receive rainfall during the growing season must have root systems that find water deep below the dry soil in the top 18 to 24 inches (50 – 60 cm) of soil profile. A tree's root system varies in width, depth, and structural characteristics with the species of tree, as well as with the soils and moisture levels. The only way to know where tree roots are growing is to find them through careful excavation, the use of an air tool or with root radar.
Critical Root Zone for Trees
A Critical Root Zone (CRZ) is the area under the tree crown where the most important roots for tree stability and survival are growing. These are the vital roots that collect nutrients and moisture for the tree, and they must be protected for the tree to survive. It is very important to determine the minimum area around the tree trunk that must be left undisturbed.
The health of the CRZ can be damaged by:
CRZ Size
Some reports indicate that the CRZ is the same as the tree's drip line. Others indicate that the CRZ will typically be represented by a concentric circle centering on the tree's trunk with a radius equal in feet to one time the number of inches of the trunk diameter. For example: The CRZ radius of a 20-inch (60 cm) diameter tree is 20 feet (7 m).
The other important factor in conserving trees during construction is the design of the structure. Flat slabs compacting and covering the CRZ will cause more damage to the soil and the tree than bridged construction where a few piers are inserted into the ground and the structure rests on the piers instead of the soil. The more soil that can be left uncovered, permeable, and uncompacted, the more groundwater infiltration, roots, and healthier soils will be retained.
CRZ Formula
In an attempt to calculate the location of a tree’s critical root zone using information such as the tree’s age, the tree's condition, and the species tolerance for root disturbance, the following CRZ formula was developed:
(dbh of tree) x (Distance from trunk – condition rating from Table) = radius (in feet) of CRZ
Critical Root Zone Determination for Trees with a Condition Rating of 2 – 5 (5 being best)
____________________________________________________________________________________
Species tolerance Tree Age Distance from Trunk / Condition Rating
________________________________________________________________4 or 5 2 or 3 Good Young (<20% of life expectancy) 0.5’ 0.62’
Mature (20 – 80% of life expectancy 0.75’ 0.94’
Over mature (>80% of life expectancy) 1.0’ 1.25’
Moderate Young 0.75’ 0.94’
Mature 1.0’ 1.25’
Over mature 1.25’ 1.56’
Poor Young 1.0’ 1.25’
Mature 1.25’ 1.56’
Over mature 1.5’ 1.88’
Note: For trees with a poor condition rating of 1, a determination should be made, with assistance of a qualified Arborist, as to whether or not the tree can be saved or is worth investing resources into.
Examples:
1) A 60-year-old, 32” dbh live oak (Quercus virginiana), with a Condition Rating of 4 (good tolerance, mature age): 32 x 0.75 = 24’ CRZ radius
2) A 15-year-old, 10” dbh tulip tree (Liriodendron tulipifera), with a Condition Rating of 2 (poor tolerance, young age): 10 x 1.25 = 12.5’ CRZ radius
Preferred CRZ Determination
Relying on formulas or guesswork alone will not suffice when engineering a parking lot to the nearest inch in elevation or the nearest fraction of a foot horizontally for a sewage line. The latest research indicates that in order to successfully determine the extent of the CRZ and to build in close proximity to significant or specimen trees, it is important to have an accurate depiction of a tree's underground structure. Because nature is variable, textbook answers and ballpark formulas will never be sufficient to make decisions on tree conservation. Site investigation, combined with field experience, the use of an air tool or root radar, is the best way to determine the CRZ location. Investigative digging is a common sense approach employed by experienced urban forestry professionals. Sample trees within representative soils and moisture levels are traced to determine representative root widths, depths and responses to particular site conditions.
It is important to know all aspects about site conditions, the available space, the construction practices, and how to select a tree species that will adapt to the site environment. These need to be based on comprehensive inventories of the urban tree resources and should assess the aesthetic, social, environmental and economic functions of the urban forest. The intent is to match and grow the right tree in the right place for the right purpose.
Critical Root Zones for Trees
by Len Phillips
Note: See 6 credit course ‘Trees on Building Sites’ for an expanded version for this article.
Field investigation and research in the last two decades have destroyed the myth that the root system extends only to the drip line of a tree's canopy. Another false myth is that all mature trees have a taproot that is the most vulnerable portion of the root system. Another perspective that dry climate trees have similar root systems to trees growing in climates that receive abundant rainfall during the growing season has to be re-considered. The trees growing in areas that do not receive rainfall during the growing season must have root systems that find water deep below the dry soil in the top 18 to 24 inches (50 – 60 cm) of soil profile. A tree's root system varies in width, depth, and structural characteristics with the species of tree, as well as with the soils and moisture levels. The only way to know where tree roots are growing is to find them through careful excavation, the use of an air tool or with root radar.
Critical Root Zone for Trees
A Critical Root Zone (CRZ) is the area under the tree crown where the most important roots for tree stability and survival are growing. These are the vital roots that collect nutrients and moisture for the tree, and they must be protected for the tree to survive. It is very important to determine the minimum area around the tree trunk that must be left undisturbed.
The health of the CRZ can be damaged by:
- cutting roots,
- excavating soil,
- applying chemicals,
- compacting the soil,
- applying any fill material or vertical barriers in the soil that impedes the flow of water or air to the roots.
CRZ Size
Some reports indicate that the CRZ is the same as the tree's drip line. Others indicate that the CRZ will typically be represented by a concentric circle centering on the tree's trunk with a radius equal in feet to one time the number of inches of the trunk diameter. For example: The CRZ radius of a 20-inch (60 cm) diameter tree is 20 feet (7 m).
The other important factor in conserving trees during construction is the design of the structure. Flat slabs compacting and covering the CRZ will cause more damage to the soil and the tree than bridged construction where a few piers are inserted into the ground and the structure rests on the piers instead of the soil. The more soil that can be left uncovered, permeable, and uncompacted, the more groundwater infiltration, roots, and healthier soils will be retained.
CRZ Formula
In an attempt to calculate the location of a tree’s critical root zone using information such as the tree’s age, the tree's condition, and the species tolerance for root disturbance, the following CRZ formula was developed:
(dbh of tree) x (Distance from trunk – condition rating from Table) = radius (in feet) of CRZ
Critical Root Zone Determination for Trees with a Condition Rating of 2 – 5 (5 being best)
____________________________________________________________________________________
Species tolerance Tree Age Distance from Trunk / Condition Rating
________________________________________________________________4 or 5 2 or 3 Good Young (<20% of life expectancy) 0.5’ 0.62’
Mature (20 – 80% of life expectancy 0.75’ 0.94’
Over mature (>80% of life expectancy) 1.0’ 1.25’
Moderate Young 0.75’ 0.94’
Mature 1.0’ 1.25’
Over mature 1.25’ 1.56’
Poor Young 1.0’ 1.25’
Mature 1.25’ 1.56’
Over mature 1.5’ 1.88’
Note: For trees with a poor condition rating of 1, a determination should be made, with assistance of a qualified Arborist, as to whether or not the tree can be saved or is worth investing resources into.
Examples:
1) A 60-year-old, 32” dbh live oak (Quercus virginiana), with a Condition Rating of 4 (good tolerance, mature age): 32 x 0.75 = 24’ CRZ radius
2) A 15-year-old, 10” dbh tulip tree (Liriodendron tulipifera), with a Condition Rating of 2 (poor tolerance, young age): 10 x 1.25 = 12.5’ CRZ radius
Preferred CRZ Determination
Relying on formulas or guesswork alone will not suffice when engineering a parking lot to the nearest inch in elevation or the nearest fraction of a foot horizontally for a sewage line. The latest research indicates that in order to successfully determine the extent of the CRZ and to build in close proximity to significant or specimen trees, it is important to have an accurate depiction of a tree's underground structure. Because nature is variable, textbook answers and ballpark formulas will never be sufficient to make decisions on tree conservation. Site investigation, combined with field experience, the use of an air tool or root radar, is the best way to determine the CRZ location. Investigative digging is a common sense approach employed by experienced urban forestry professionals. Sample trees within representative soils and moisture levels are traced to determine representative root widths, depths and responses to particular site conditions.
It is important to know all aspects about site conditions, the available space, the construction practices, and how to select a tree species that will adapt to the site environment. These need to be based on comprehensive inventories of the urban tree resources and should assess the aesthetic, social, environmental and economic functions of the urban forest. The intent is to match and grow the right tree in the right place for the right purpose.
Fixing Compact Soils
Edited by Len Phillips and R W Gibney RLA - ISA
Compacted soils occur when developers come in with heavy equipment to build structures, install utilities, and layout streets and sidewalks. They need to have compacted soil so foundations do not settle and sidewalks and streets would not crack. While this process may be good for development, it is not good for growing trees and other plants. Their roots cannot penetrate the compact soil in sufficient quantity to support tree growth.
Prevention of Soil Compaction
There are several steps an arborist can take to prevent damage to soils from compaction during the construction process.
Treatment of Compacted Soils
If the prevention efforts were not applied to the site and the soil is severely compacted, there are several steps an arborist can take to encourage root growth in compact soils. Some of these efforts were developed for agricultural fields, but they apply to large areas where tree roots are expected to be growing years after construction is complete. They include the following:
Follow-up after Treatment
The landscape architect should access the extent and quality of the compacted soil prior to planting any trees. Monitor the treatments to be sure they were effective and covered the area sufficiently. Most of the products mentioned above should be applied by air tillage or cores, followed by mulch and/or compost surface treatments as necessary for nutrient replacement.
Often several years are required to determine the effectiveness of the treatments. In locations where treatments were not applied, as evidence by historic dirt roads, the compacted wheel ruts are still visible 100 years after the use of the road ceased.
Source:
Scharenbroch, Dr. Bryant, “Fix Compact Soils”, lecture, November 2016.
Edited by Len Phillips and R W Gibney RLA - ISA
Compacted soils occur when developers come in with heavy equipment to build structures, install utilities, and layout streets and sidewalks. They need to have compacted soil so foundations do not settle and sidewalks and streets would not crack. While this process may be good for development, it is not good for growing trees and other plants. Their roots cannot penetrate the compact soil in sufficient quantity to support tree growth.
Prevention of Soil Compaction
There are several steps an arborist can take to prevent damage to soils from compaction during the construction process.
- Prior to the start of construction, the soil where trees exist or are to be planted should be protected from compaction. This is most easily done by installing fencing around the tree's drip line and other areas where roots are expected to be growing. The intent of the fencing is to keep construction equipment away from the root zone of the existing and proposed trees, but this step must be monitored throughout the project. At the same time a deep layer of wood chips or other mulch should be spread over the root zone of all the existing and future trees to absorb the compression of heavy machinery on surrounding soils.
- All equipment must be kept off of wet soil. Compaction of wet soil will result in irreversibly damaged soil. Wet soil has water in the pore spaces making the soil elastic and easily crushed. The crushed soil then no longer has the pore space that is essential for containing oxygen and water molecules that are needed by the tree roots for survival.
Treatment of Compacted Soils
If the prevention efforts were not applied to the site and the soil is severely compacted, there are several steps an arborist can take to encourage root growth in compact soils. Some of these efforts were developed for agricultural fields, but they apply to large areas where tree roots are expected to be growing years after construction is complete. They include the following:
- Replace the compacted soil with suspended pavements, structural soils, or soil cells prior to installing surface pavements, curbs, etc.
- Soils only marginally compacted can be improved with the addition of:
- biosolids which have a high nutrient content and are products of sewage treatment facilities.
- biochar which is not a fertilizer but has large pores and are composed of pure carbon, that will improve soil quality.
- biosolids and biochar together provide an effective treatment for many marginally compacted soils.
- compost which contains a wide variety of micro-organisms and nutrients makes a good soil amendment.
- composted woodchips that are often used in conjunction with compost or after a compost treatment will provide a long period for compaction treatment.
- mulch on the surface provides long-term nutrient replacements.
- Consider manipulation of heavily compacted soil with:
- backhoes that can dig holes and trenches to loosen the soil as it is being replaced by dropping the soil from 6 ft. above the surface. Compost should be added in the same manner.
- trenching equipment can loosen the soil to provide a channel that directs root growth to non-compact soils beyond the construction limits.
- vertical boring of 2 inch diameter holes 18 in. apart within the root zone of existing and proposed trees should be at least 18 in. deep. The holes may receive fertilizer and other amendments prior to the soil being replaced in the holes.
- air tillage (Air Spade™) may be used to blow the compact soil off of all the roots so it can be pulled back over the roots in a non-compacting manner.
- an aerator attachment to a small, light weight tractor with balloon tires will loosen the top 6 to 8 inches of soil by punching holes in the soil. This equipment may require several repeated treatments to relieve severe compaction and the tines may occasionally damage existing unseen roots.
- a subsoiler is a large probe in the shape of a fish hook, that is lowered into the soil and pulled through the compact soil to the depth and area necessary. This process needs a powerful light weight tractor with balloon tires to pull the hook in heavily compacted soil.
- plows on the back of a tractor will loosen the soil in the same manner as the subsoiler, but only 8 to 10 inches deep. If the soil is wet when the plow is used, the bottom of the plow will sometimes seal the bottom of the trench and prevent water penetration below the plow depth.
- rotary tillers are very effective at loosening the soil but they are limited in the depth to which they can work by their design and the engine power. Very large tillers that attach to tractors can go as deep as 18 inches.
- add soil amendments such as mulches, compost, and fertilizers on the surface prior to the start of a manipulation so the amendment is worked into the improved, non-compacted soil.
Follow-up after Treatment
The landscape architect should access the extent and quality of the compacted soil prior to planting any trees. Monitor the treatments to be sure they were effective and covered the area sufficiently. Most of the products mentioned above should be applied by air tillage or cores, followed by mulch and/or compost surface treatments as necessary for nutrient replacement.
Often several years are required to determine the effectiveness of the treatments. In locations where treatments were not applied, as evidence by historic dirt roads, the compacted wheel ruts are still visible 100 years after the use of the road ceased.
Source:
Scharenbroch, Dr. Bryant, “Fix Compact Soils”, lecture, November 2016.
Living Mulches
By Len Phillips
In the practice of general plant care, a living mulch is a ground cover plant growing at the base of a tree. Living mulches are sometimes used at locations where the tree is growing in a sidewalk tree cut-out and the living mulch (plants) are growing around the tree. The living mulch is intended to beautify and replace the need for a tree grate or conventional mulch by using plants to provide weed suppression, control of the soil temperature, and a visual means to discourage people from walking close to the tree and causing soil compaction. Living mulches can reduce water runoff and erosion, and filter surface water runoff for use by the tree. Living mulches have also been shown to increase the population of organisms which enhance the quality of the soil. Living mulches are intended to grow for many years in harmony with the tree. Opponents of this concept believe the living mulch robs the tree of soil moisture, nutrients, and microorganisms. But the fact is that these plants actually help the tree by preventing evaporation of soil moisture and converting nutrients into forms that are useful for the tree.
Plant selection for creating a living mulch is not an easy task. While just about any plant might grow in harmony with a tree in a conventional landscape, very few will thrive living in the sidewalk cutout surrounded by concrete. The planting of the ground covers may occur anytime including right after the tree has been planted. The plants should be planted on a grade of no more than 1 inch (2.5 cm) below the sidewalk elevation to hold runoff water for the plants and tree. The living mulch plants should be carefully placed around the outside edge of the sidewalk cutout to avoid any conflict with the newly developing tree roots and the underground root stabilizing system.
Never plant anything within 12" (30 cm) of the flare. No part of the tree's trunk and bark should ever be covered with anything that retains moisture. Doing so encourages rot. In addition, any planting of small ground covers needs to be done carefully so as not to damage the existing tree's roots. Open areas should still be mulched with composted wood chips so the soil is never left bare.
Most Desirable Living Mulches
The following, in this author's opinion, are the best living mulches because they are vigorous ground covers and will tolerate pedestrian traffic, winter snow plow damage, and erratic weather conditions:
White clover Trifolium repens; Clovers with their deep roots, provide resistance to soil compaction. Legume living mulches also have some important positive effects on the nutrient cycling that benefit the tree. For example, clover fixes the atmospheric nitrogen that is important for tree growth and it is effective for enhancing and recycling the soil's nutrients. Clover has the ability to grow in sun or shade, maintain a low profile, thrive if repeatedly mowed and it will withstand foot traffic. It is considered by many as the best choice for a living mulch. In established stands, it also may provide some nitrogen suitable for use by the tree. Photo
Vinca Vinca minor; Vinca does well in all light conditions and, once established, is fairly tolerant of a less than desirable site and soil conditions. Vinca is a shallow rooted creeper that tolerates soil compaction and pedestrian foot traffic, once it is established. It should be planted with quart size plants that have large root systems to reduce the time for the plant to become established. These larger plants are quite developed and fewer plants are needed so there's a lot less disturbance in the sidewalk cutout area. Impact on the tree is minimal.
Creepers
Creepers are plants that can grow to cover the soil from the outside edge of the sidewalk cutout where there is more light, and they may grow toward the trunk of the tree with time. These are all shallow-rooted perennials with roots in the top 6 inches (15 cm) of soil, and therefore, above the tree's main roots. They are all tolerant of varying sun exposures. Creepers do require weeding and extra water for the first few years but once established, the plants look outstanding all year. All the plants cool the roots and discourage any compacting foot traffic. Reports indicate that there has to be some assumed nutrient competition between tree and the ground cover but these reports also indicate that both the tree and the creepers appear to be living in harmony. Some of the best creepers for this function, include:
Undesirable Living Mulches
Not only are the plants listed below considered invasive in many locations, they can also cause moisture retention, root rot, and other problems for the tree. Many of these plants can also climb over the entire tree. NOT recommended are:
Caution
Not all trees are created equal. Each requires specific light, soil, and moisture conditions to survive and remain healthy. Some tree species are extremely sensitive to major soil disturbance. Planting beneath trees that are sensitive to having their roots disturbed may need to have the proposed plantings scaled back or carried out over a few years.
Source
The test that follows contains 30 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test.
LA CES will award 1.0 PDH (HSW) credit for a passing grade. North Carolina Board of LA and New Jersey Board of Architects will award 1.0 credits for a passing grade.
The cost for taking this test is $20 per credit. If you purchase an annual subscription for 12 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report your passing test score to LA CES. If you are also ISA* certified we will report your passing score to ISA for no additional cost. Please be sure to add your ISA Certification number when you sign in. Tests with passing scores may be submitted only once to each organization.
*ISA has approved this course for .5 CEUs per section for a total of 1.5 CEUs. Critical Root Zones for Trees section is applied toward Certified Arborist, Municipal Specialist, or BCMA management credits. Fixing Compact Soils and Living Mulches sections is applied toward Certified Arborist, Municipal Specialist, or BCMA practice credits.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment 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. If you are an ISA and/or CLARB member, please be sure to include your certification/member number(s) along with your LA license and ASLA numbers.
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. 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.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option.
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.
LA CES maintains a record of earned PDH credits on their website http://laces.asla.org/
ISA maintains a record of earned CEU credits on their website http://www.isa-arbor.com/
By Len Phillips
In the practice of general plant care, a living mulch is a ground cover plant growing at the base of a tree. Living mulches are sometimes used at locations where the tree is growing in a sidewalk tree cut-out and the living mulch (plants) are growing around the tree. The living mulch is intended to beautify and replace the need for a tree grate or conventional mulch by using plants to provide weed suppression, control of the soil temperature, and a visual means to discourage people from walking close to the tree and causing soil compaction. Living mulches can reduce water runoff and erosion, and filter surface water runoff for use by the tree. Living mulches have also been shown to increase the population of organisms which enhance the quality of the soil. Living mulches are intended to grow for many years in harmony with the tree. Opponents of this concept believe the living mulch robs the tree of soil moisture, nutrients, and microorganisms. But the fact is that these plants actually help the tree by preventing evaporation of soil moisture and converting nutrients into forms that are useful for the tree.
Plant selection for creating a living mulch is not an easy task. While just about any plant might grow in harmony with a tree in a conventional landscape, very few will thrive living in the sidewalk cutout surrounded by concrete. The planting of the ground covers may occur anytime including right after the tree has been planted. The plants should be planted on a grade of no more than 1 inch (2.5 cm) below the sidewalk elevation to hold runoff water for the plants and tree. The living mulch plants should be carefully placed around the outside edge of the sidewalk cutout to avoid any conflict with the newly developing tree roots and the underground root stabilizing system.
Never plant anything within 12" (30 cm) of the flare. No part of the tree's trunk and bark should ever be covered with anything that retains moisture. Doing so encourages rot. In addition, any planting of small ground covers needs to be done carefully so as not to damage the existing tree's roots. Open areas should still be mulched with composted wood chips so the soil is never left bare.
Most Desirable Living Mulches
The following, in this author's opinion, are the best living mulches because they are vigorous ground covers and will tolerate pedestrian traffic, winter snow plow damage, and erratic weather conditions:
White clover Trifolium repens; Clovers with their deep roots, provide resistance to soil compaction. Legume living mulches also have some important positive effects on the nutrient cycling that benefit the tree. For example, clover fixes the atmospheric nitrogen that is important for tree growth and it is effective for enhancing and recycling the soil's nutrients. Clover has the ability to grow in sun or shade, maintain a low profile, thrive if repeatedly mowed and it will withstand foot traffic. It is considered by many as the best choice for a living mulch. In established stands, it also may provide some nitrogen suitable for use by the tree. Photo
Vinca Vinca minor; Vinca does well in all light conditions and, once established, is fairly tolerant of a less than desirable site and soil conditions. Vinca is a shallow rooted creeper that tolerates soil compaction and pedestrian foot traffic, once it is established. It should be planted with quart size plants that have large root systems to reduce the time for the plant to become established. These larger plants are quite developed and fewer plants are needed so there's a lot less disturbance in the sidewalk cutout area. Impact on the tree is minimal.
Creepers
Creepers are plants that can grow to cover the soil from the outside edge of the sidewalk cutout where there is more light, and they may grow toward the trunk of the tree with time. These are all shallow-rooted perennials with roots in the top 6 inches (15 cm) of soil, and therefore, above the tree's main roots. They are all tolerant of varying sun exposures. Creepers do require weeding and extra water for the first few years but once established, the plants look outstanding all year. All the plants cool the roots and discourage any compacting foot traffic. Reports indicate that there has to be some assumed nutrient competition between tree and the ground cover but these reports also indicate that both the tree and the creepers appear to be living in harmony. Some of the best creepers for this function, include:
- Ajuga Ajuga reptans
- Peanut Arachis repens
- Epimedium Epimedium spp.
- Wild Woodland Strawberry Fragaria vesca Photo
- Coral Bells Heuchera spp.
- Mini and dwarf Hosta varieties Hosta spp. Photo
- Yellowroot (Golden Seal) Hydrastis canadensis Photo
- Liriope Liriope muscari Photo
- Cupflower Mazus repens Photo
- Pachysandra Pachysandra Photo
- Ginseng Panax quinquefolius Photo
- Woodland Phlox Phlox divaricata
- Stonecrop Sedum spp. Photo
- Comfrey Symphytum officinale Photo
- Creeping Thyme Thymus serpyllum Photo
- Turkish Speedwell Veronica liwanensis Photo
- Barren Strawberry Waldsteinia ternata Photo
- Hardy Ferns – Several species are suitable for living mulch, especially in somewhat shady areas.
Undesirable Living Mulches
Not only are the plants listed below considered invasive in many locations, they can also cause moisture retention, root rot, and other problems for the tree. Many of these plants can also climb over the entire tree. NOT recommended are:
- Porcelain Berry Ampelopsis brevipedunculata
- Climbing Euonymus Euonymus fortunei
- English Ivy Hedera helix
- Kudzu Pueraria lobata
- Bittersweet Solanum dulcamara
- Poison Ivy Toxicodendron radicans
- Grape Vitis spp.
- Wisteria Wisteria spp.
- Annuals - Growing annuals under young trees is the exception to being good for trees. Annuals are aggressive growers and they can cause growth reduction to the tree because of the competition for soil nutrients. Annuals also need lots of water and weekly maintenance.
- Shrubs - Often young trees have been planted and combined with nice flowering shrubs. Over time the trees will win the competition and the shrubs look terrible and need to be removed, so they are not a good choice in the sidewalk cut out areas.
- Juniperus horizontalis – Creeping Juniper is a very popular group of junipers that require a lot of maintenance to keep them from growing over the flare and sidewalk, while also encouraging pest and disease problems causing harm to the tree. These problems are in addition to the problems mentioned above with annuals and shrubs.
Caution
Not all trees are created equal. Each requires specific light, soil, and moisture conditions to survive and remain healthy. Some tree species are extremely sensitive to major soil disturbance. Planting beneath trees that are sensitive to having their roots disturbed may need to have the proposed plantings scaled back or carried out over a few years.
Source
- Special thanks to members of LinkedIn's Urban Forestry discussion group for sharing their favorite living mulches.
The test that follows contains 30 questions. Before taking the test be sure you have read the article carefully. The passing grade is 80% on the entire test.
LA CES will award 1.0 PDH (HSW) credit for a passing grade. North Carolina Board of LA and New Jersey Board of Architects will award 1.0 credits for a passing grade.
The cost for taking this test is $20 per credit. If you purchase an annual subscription for 12 credits, the cost per credit is reduced by 50% (see Annual Subscription link below). We will report your passing test score to LA CES. If you are also ISA* certified we will report your passing score to ISA for no additional cost. Please be sure to add your ISA Certification number when you sign in. Tests with passing scores may be submitted only once to each organization.
*ISA has approved this course for .5 CEUs per section for a total of 1.5 CEUs. Critical Root Zones for Trees section is applied toward Certified Arborist, Municipal Specialist, or BCMA management credits. Fixing Compact Soils and Living Mulches sections is applied toward Certified Arborist, Municipal Specialist, or BCMA practice credits.
To take the test by the pay per test option, click on the 'Pay Now' button below where you can send payment 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. If you are an ISA and/or CLARB member, please be sure to include your certification/member number(s) along with your LA license and ASLA numbers.
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. 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.
Test re-takes are allowed, however you will have to pay for the retake if you are using the pay per test option.
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.
LA CES maintains a record of earned PDH credits on their website http://laces.asla.org/
ISA maintains a record of earned CEU credits on their website http://www.isa-arbor.com/