#5 Read About Urban Tree Installation
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.
Specifications for Quality Nursery Trees
The Specification for Quality Nursery Trees can now be found in the Specification Section of our website. To read this specification, click here. If you plan on taking the test for CEU's on this Topic 5, please follow the link to read the specification because test questions on this spec are asked on the Topic 5 test at the bottom of this page.
Specifications for Quality Nursery Trees
The Specification for Quality Nursery Trees can now be found in the Specification Section of our website. To read this specification, click here. If you plan on taking the test for CEU's on this Topic 5, please follow the link to read the specification because test questions on this spec are asked on the Topic 5 test at the bottom of this page.
General Tree Installation
Street trees in the city should be nursery grown in order to obtain the highest quality product possible. High quality is essential because of the difficult environment street trees will have to deal with.
Amending the Planting Site Soil
After planting a tree, it is best to create a uniform mix throughout the transition zone where the roots must grow. Recent research indicates that amendments such as peat moss, compost, composted manure, or hydrogels will enhance soil water retention when mixed with the parent material. Moreover, adding no more than one-third (by volume) of a well-composted source of organic matter will reduce compaction when worked into the top 24" - 36" (60-90 cm) of a planting bed. Too much soil amendment, however, can create shrinkage, moisture gradients, and cause the roots to be confined to the planting hole.
Never backfill the planting pit with only a soil amendment! If an amendment is going to be made based on the soil conditions, it should be applied in a manner necessary to correct soil deficiencies and in the largest area possible. For example, if the soil is sandy, it may be necessary to add a 4" - 5" (10 - 12 cm) layer of compost, mixed into the top 24" (60 cm) of previously tilled topsoil. If the soil is clay it may be necessary to add 9" - 10" (21 - 23 cm) of compost to loosen the soil for proper root development.
Tree Installation
With or without amendments, a large planting area should be loosened to expedite root growth. The sooner the roots are able to grow into the surrounding soil; the sooner the tree will become established and recover from transplant shock. Loosen the surrounding soil down to the depth of the tree's root system, and horizontally to a distance of at least three times the length of the roots. By loosening any compacted soil, cracks and fissures will provide avenues of growth and expansion for the newly developing roots. Video
In the center of the prepared area, dig a shallow hole to set the tree. The planting hole must be wide enough to accommodate the roots without bending any. The hole should allow the root ball to sit on solid but not compacted ground rather than in loose soil. Once the tree is set in the hole, the flare should be level with or 1 inch (3 cm) above the final soil level. Position the tree so that it is vertical and its branches will cause no harm to abutters.
Drainage is vital to the tree's survival and must be correct at installation time. Small trees have a shallow root ball and are better suited for installation on wet sites. If large-sized nursery stock is absolutely necessary for a poorly drained site, purchase trees with a shallow root ball or plant on a mound to keep the roots above the water table.
When the installation is finished, consider building a berm of mulch (preferred) or soil (less preferred) around the root ball circumference to hold rain and irrigation water. Keep this saucer less than 4 inches high. It is more appropriate to make the berm from mulch since the berm typically ends up on top of the root ball where mulch is desirable. Breach or remove the berm just before the first solid freeze of winter so water is not trapped on the surface.
Installing on Slopes
Early practice suggested the tree be installed with the flare on grade or one inch (2.5 cm) higher and there would be a cut on the uphill half of the tree pit and fill on the lower half. However, current research requires that the root flare should be one inch (2.5 cm) higher than the uphill side to prevent the tree from being installed too deep. The root ball on the downhill side will be covered with a mound of fill.
Mulching
Two to four inches of organic mulch around the tree results in a noticeably improved survival rate, transplant shock recovery, and subsequent growth. Combined with adequate irrigation on a regular basis, mulch is the most effective measure to ensure tree installation success. Remember to keep the mulch away from directly touching the trunk.
Watering
Supplying adequate water to trees insures plant survival and long-term health. Poorly drained soil is the most common cause of plant mortality. Never put rocks or gravel in the bottom of the hole to improve drainage unless it is connected to a drain system.
Pruning
During installation, remove all dead, damaged, or weak branches and roots along with one of any co-dominant leaders. Also, consider whether pruning for corrections of structural defects should be done now or wait until the tree is established in a couple of years. There is no need to remove a third of the top growth. Research has proven that this heavy pruning, intended to compensate for root loss, has no benefit whatsoever and may even retard the tree's recovery from the transplanting root loss. Trees need every possible leaf to make the food necessary to replace the missing roots.
Weed Control
Weeds in the root ball must be controlled by hand pulling or with mulch. Small nursery stock may be the better choice for weed control because small trees establish and grow quickly and are better able to compete with weeds.
Collected Trees
Native trees are sometimes collected from natural stands and transplanted to landscape sites. If held in a nursery for two years, they are considered to be nursery grown. Research indicates that root balls on collected trees are similar to those on nursery-grown trees but have fewer fine roots. In addition, they often have a thinner canopy until they become established. Collected trees do grow slower after transplanting than trees from nursery production systems because of their lack of fine roots.
Comparison Between Installation Techniques
Trees can be purchased in several different ways. It is possible to install some species at any time of the year depending upon the choices of nursery stock and installation methods. Those in hard plastic containers or boxes are most resistant to abusive handling; those in soft, fabric containers and those that are B&B (balled & burlapped) are less sensitive. Bare root trees are the least sensitive to abuse, but will recover the fastest because there is no soil adaptation required. On the other hand, bare root trees do require special attention to ensure a rapid response to the transplanting.
B&B trees and shrubs are dug with a firm ball of soil around the roots and held securely in place with burlap, twine, and usually a wire basket. The soil ball protects tree roots from water stress during the installation process. Field-grown plants are best moved while they are dormant. B&B trees are generally produced for homes, parks, and street tree installation projects. The vast majority of B&B trees are dug at less than 4" trunk diameter but special large trees are dug this way as well.
Bare Root (BR) trees are dug and stored without any soil around their roots. Bare root trees must be installed while dormant and are ideal for the challenges of urban environments. The BR method utilizes trees up to two inches in caliper and can be substituted for the B&B tree at half the cost to purchase and install, while still offering excellent rates of survival and growth However, BR tree roots are susceptible to drying out and must be kept moist at all times. For more information on Bare Root trees see Topic #7.
Containerized trees are convenient and less expensive than B&B trees, but more than BR trees. They can be installed anytime the ground is not frozen and are usually easier to handle than B&B or BR trees. Shoot and trunk growth appear to be similar between B&B and BR trees. Containerized trees appear to be more susceptible to desiccation, death, and slower growth until they become established if the roots are not kept moist after installation and for several months until they appear established. They have a good survival rate because there is a higher root regeneration capacity. However, they also have the highest probability of root malformation, which can lead to girdling roots, instability, and shortened life span.
Grow Bags are about half the volume of the root balls of field-grown trees, which makes them easier to handle. Research shows that because the root ball is smaller, there is less water storage capacity. This makes trees in grow bags more sensitive to desiccation immediately after digging than are B&B trees grown directly in the field.
Installing Season
Expected weather conditions during the weeks after installation are very important in determining the time for transplanting shock recovery. Extended periods of moderately warm soil temperatures and adequate soil moisture are ideal for promoting active root growth and minimizing stress. The absence of rainfall need not delay installation if irrigation is available during and after planting.
Autumn Installation
Autumn installation of trees is often done because certain species focus on root system development in autumn. Most other species regenerate new roots better when installed in spring. Autumn installation is successful if the plants are mulched and there is at least 4 weeks before the soil temperature drops below 40° F (4° C). Evergreens installed in autumn need several weeks of soil temperature in the 60°-70° F (15°-20° C) range for root growth. Evergreens must be well established before the ground is too cold to obtain the necessary moisture needed to balance water loss through their needles in winter. Installing trees on sites exposed to excessive wind should be delayed until spring, if possible. During the first winter after installation, evergreens should be shielded from prevailing winds by using some form of wind barriers.
Installation Out Of Season
The best option if installing trees out of season is required, is to install containerized trees. If a tree must be dug in full leaf, the tree should have been root pruned at the nursery several weeks prior to digging. The tree should be hand dug so the root ball is balled and burlapped in the hole. The root ball must be soaked and kept in a shady misting area for three to seven days until the new growth has hardened off. During the hardening off period, roots begin to regenerate within the root ball, and the tree may drop some leaves. Purchasing freshly dug trees that are not hardened-off is not recommended unless you have assurances that they were regularly root pruned during production, have fibrous roots, and the leaves were misted for a week before the sale.
The tree should be installed as soon as possible. It is also critical that the tree be watered twice, immediately after installing, and then watering should be done at least twice a week for the rest of the growing season.
Installing with a pneumatic soil excavating tool (Air-Spade®) or a tree spade may be more successful in the summer than B&B because the root ball can be over-sized and the fine roots are disturbed less.
Winter Planting
Some tree species can be installed when the soil ball is frozen. Large soil balls can be easier to handle and transport with less chance that the ball will crack and damage the roots. Frozen ground provides better access for heavy equipment at both the digging and the installation site. Sugar maple (Acer saccharum), pine (Pinus sp.), honeylocust (Gleditsia triacanthos), elm (Ulmus sp.), linden (Tilia sp.), and crabapple (Malus sp.) are species most suited for winter installation. Red oak (Quercus rubra), dogwood (Cornus florida), hemlock (Tsuga canadensis), sycamore (Platanus occidentalis), sweetgum (Liquidambar styraciflua), birch (Betula sp.), and magnolia (Magnolia sp.) are less likely to survive.
Some nurseries dig trees when the ground is frozen. The frozen surface of the ball replaces the burlap and wire basket. The frozen ball is actually only frozen a few inches around the root ball surface and must not be allowed to thaw out or freeze solid until it is installed. The installation hole must be kept mulched before the tree is installed so the backfill soil is not frozen. This practice requires so much attention to freezing and thawing it is no longer encouraged.
Easily Installed Trees
Scientific name Common name
Abies sp. Fir
Acacia longifolia Acacia
Acer campestre Hedge maple
Acer x freemanii Freeman Maple
Acer miyabei Miyabei Maple
Acer nigrum Black maple
Acer platanoides Norway maple
Acer pseudoplatanus Sycamore maple
Acer rubrum Red maple
Acer saccharinum Silver maple
Acer saccharum Sugar maple
Acer tartaricum Tartaricum Maple
Acer tartaricum ssp. ginnala Amur Maple
Aesculus sp. Buckeye
Aesculus hippocastanum Horsechestnut
Aesculus x carnea Red Horsechestnut
Ailanthus altissima Tree of heaven
Alnus sp Alder
Amelanchier sp. Serviceberry
Casuarina equisetifolia Australian pine
Catalpa sp. Catalpa
Celtis sp. Hackberry
Cercidiphyllum japonicum Katsura tree
Cercis canadensis American redbud
Chionanthus virginicus White fringe tree
Cladrastis kentukea Yellowwood
Clusia rosea Pitch apple
Cocos nucifera Coconut palm
Cornus mas Cornelian cherry Dogwood
Crataegus sp. Hawthorn
Cupaniopsis anacardioides Carrotwood
Elaeagnus angustifolia Russian olive
Fraxinus sp. Ash
Fraxinus quadrangulata Blue ash
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Jacaranda mimosifolia Jacaranda
Juniperus sp. Juniper
Koelreuteria paniculata Goldenraintree
Laburnum x watereri Goldenchain tree
Larix laricina American larch
Liriodendron tulipifera Tulip tree/yellow poplar
Maclura pomifera Osage orange
Malus sp. Apple, crabapple
Morus sp. Mulberry
Paulownia tomentosa Paulownia
Parrotia persica Persian Parrotia
Persea borbonia Redbay
Phellodendron sp. Corktree
Picea abies Norway spruce
Picea glauca White spruce
Picea pungens Colorado spruce
Pinus nigra Austrian pine
Pinus sp. Pine
Platanus sp. Plane tree
Populus sp. Poplar
Prunus 'Accolade' Accolade Flowering Cherry
Prunus sargentii Sargent Cherry
Prunus virginiana 'Canada Red' Chokecherry
Prunus serotina Black cherry
Pseudolarix amabilis Golden larch
Pyrus calleryana Callery pear
Pyrus betulafolia Birchleaf Pear
Pyrus fauriei 'Westwood' Korean Sun Pear
Pyrus ussuriensis Ussarian Pear
Quercus bicolor Swamp White Oak
Quercus imbricaria Shingle oak
Quercus laurifolia Laurel oak
Quercus palustris Pin oak
Quercus phellos Willow oak
Quercus robur English oak
Quercus virginiana Southern live oak
Rhamnus cathartica Common buckthorn
Robinia sp. Black Locust
Sabal palmetto Cabbage palm
Salix sp. Willow
Sorbus sp. Mountain ash
Syringa reticulata Japanese Tree Lilac
Taxus sp. Yew
Thuja occidentalis Arborvitae, white cedar
Tilia sp. Linden, lime
Tsuga sp. Hemlock
Ulmus sp. Elm
Ulmus pumila Siberian elm
Zelkova serrate Zelkova
Street trees in the city should be nursery grown in order to obtain the highest quality product possible. High quality is essential because of the difficult environment street trees will have to deal with.
Amending the Planting Site Soil
After planting a tree, it is best to create a uniform mix throughout the transition zone where the roots must grow. Recent research indicates that amendments such as peat moss, compost, composted manure, or hydrogels will enhance soil water retention when mixed with the parent material. Moreover, adding no more than one-third (by volume) of a well-composted source of organic matter will reduce compaction when worked into the top 24" - 36" (60-90 cm) of a planting bed. Too much soil amendment, however, can create shrinkage, moisture gradients, and cause the roots to be confined to the planting hole.
Never backfill the planting pit with only a soil amendment! If an amendment is going to be made based on the soil conditions, it should be applied in a manner necessary to correct soil deficiencies and in the largest area possible. For example, if the soil is sandy, it may be necessary to add a 4" - 5" (10 - 12 cm) layer of compost, mixed into the top 24" (60 cm) of previously tilled topsoil. If the soil is clay it may be necessary to add 9" - 10" (21 - 23 cm) of compost to loosen the soil for proper root development.
Tree Installation
With or without amendments, a large planting area should be loosened to expedite root growth. The sooner the roots are able to grow into the surrounding soil; the sooner the tree will become established and recover from transplant shock. Loosen the surrounding soil down to the depth of the tree's root system, and horizontally to a distance of at least three times the length of the roots. By loosening any compacted soil, cracks and fissures will provide avenues of growth and expansion for the newly developing roots. Video
In the center of the prepared area, dig a shallow hole to set the tree. The planting hole must be wide enough to accommodate the roots without bending any. The hole should allow the root ball to sit on solid but not compacted ground rather than in loose soil. Once the tree is set in the hole, the flare should be level with or 1 inch (3 cm) above the final soil level. Position the tree so that it is vertical and its branches will cause no harm to abutters.
Drainage is vital to the tree's survival and must be correct at installation time. Small trees have a shallow root ball and are better suited for installation on wet sites. If large-sized nursery stock is absolutely necessary for a poorly drained site, purchase trees with a shallow root ball or plant on a mound to keep the roots above the water table.
When the installation is finished, consider building a berm of mulch (preferred) or soil (less preferred) around the root ball circumference to hold rain and irrigation water. Keep this saucer less than 4 inches high. It is more appropriate to make the berm from mulch since the berm typically ends up on top of the root ball where mulch is desirable. Breach or remove the berm just before the first solid freeze of winter so water is not trapped on the surface.
Installing on Slopes
Early practice suggested the tree be installed with the flare on grade or one inch (2.5 cm) higher and there would be a cut on the uphill half of the tree pit and fill on the lower half. However, current research requires that the root flare should be one inch (2.5 cm) higher than the uphill side to prevent the tree from being installed too deep. The root ball on the downhill side will be covered with a mound of fill.
Mulching
Two to four inches of organic mulch around the tree results in a noticeably improved survival rate, transplant shock recovery, and subsequent growth. Combined with adequate irrigation on a regular basis, mulch is the most effective measure to ensure tree installation success. Remember to keep the mulch away from directly touching the trunk.
Watering
Supplying adequate water to trees insures plant survival and long-term health. Poorly drained soil is the most common cause of plant mortality. Never put rocks or gravel in the bottom of the hole to improve drainage unless it is connected to a drain system.
Pruning
During installation, remove all dead, damaged, or weak branches and roots along with one of any co-dominant leaders. Also, consider whether pruning for corrections of structural defects should be done now or wait until the tree is established in a couple of years. There is no need to remove a third of the top growth. Research has proven that this heavy pruning, intended to compensate for root loss, has no benefit whatsoever and may even retard the tree's recovery from the transplanting root loss. Trees need every possible leaf to make the food necessary to replace the missing roots.
Weed Control
Weeds in the root ball must be controlled by hand pulling or with mulch. Small nursery stock may be the better choice for weed control because small trees establish and grow quickly and are better able to compete with weeds.
Collected Trees
Native trees are sometimes collected from natural stands and transplanted to landscape sites. If held in a nursery for two years, they are considered to be nursery grown. Research indicates that root balls on collected trees are similar to those on nursery-grown trees but have fewer fine roots. In addition, they often have a thinner canopy until they become established. Collected trees do grow slower after transplanting than trees from nursery production systems because of their lack of fine roots.
Comparison Between Installation Techniques
Trees can be purchased in several different ways. It is possible to install some species at any time of the year depending upon the choices of nursery stock and installation methods. Those in hard plastic containers or boxes are most resistant to abusive handling; those in soft, fabric containers and those that are B&B (balled & burlapped) are less sensitive. Bare root trees are the least sensitive to abuse, but will recover the fastest because there is no soil adaptation required. On the other hand, bare root trees do require special attention to ensure a rapid response to the transplanting.
B&B trees and shrubs are dug with a firm ball of soil around the roots and held securely in place with burlap, twine, and usually a wire basket. The soil ball protects tree roots from water stress during the installation process. Field-grown plants are best moved while they are dormant. B&B trees are generally produced for homes, parks, and street tree installation projects. The vast majority of B&B trees are dug at less than 4" trunk diameter but special large trees are dug this way as well.
Bare Root (BR) trees are dug and stored without any soil around their roots. Bare root trees must be installed while dormant and are ideal for the challenges of urban environments. The BR method utilizes trees up to two inches in caliper and can be substituted for the B&B tree at half the cost to purchase and install, while still offering excellent rates of survival and growth However, BR tree roots are susceptible to drying out and must be kept moist at all times. For more information on Bare Root trees see Topic #7.
Containerized trees are convenient and less expensive than B&B trees, but more than BR trees. They can be installed anytime the ground is not frozen and are usually easier to handle than B&B or BR trees. Shoot and trunk growth appear to be similar between B&B and BR trees. Containerized trees appear to be more susceptible to desiccation, death, and slower growth until they become established if the roots are not kept moist after installation and for several months until they appear established. They have a good survival rate because there is a higher root regeneration capacity. However, they also have the highest probability of root malformation, which can lead to girdling roots, instability, and shortened life span.
Grow Bags are about half the volume of the root balls of field-grown trees, which makes them easier to handle. Research shows that because the root ball is smaller, there is less water storage capacity. This makes trees in grow bags more sensitive to desiccation immediately after digging than are B&B trees grown directly in the field.
Installing Season
Expected weather conditions during the weeks after installation are very important in determining the time for transplanting shock recovery. Extended periods of moderately warm soil temperatures and adequate soil moisture are ideal for promoting active root growth and minimizing stress. The absence of rainfall need not delay installation if irrigation is available during and after planting.
Autumn Installation
Autumn installation of trees is often done because certain species focus on root system development in autumn. Most other species regenerate new roots better when installed in spring. Autumn installation is successful if the plants are mulched and there is at least 4 weeks before the soil temperature drops below 40° F (4° C). Evergreens installed in autumn need several weeks of soil temperature in the 60°-70° F (15°-20° C) range for root growth. Evergreens must be well established before the ground is too cold to obtain the necessary moisture needed to balance water loss through their needles in winter. Installing trees on sites exposed to excessive wind should be delayed until spring, if possible. During the first winter after installation, evergreens should be shielded from prevailing winds by using some form of wind barriers.
Installation Out Of Season
The best option if installing trees out of season is required, is to install containerized trees. If a tree must be dug in full leaf, the tree should have been root pruned at the nursery several weeks prior to digging. The tree should be hand dug so the root ball is balled and burlapped in the hole. The root ball must be soaked and kept in a shady misting area for three to seven days until the new growth has hardened off. During the hardening off period, roots begin to regenerate within the root ball, and the tree may drop some leaves. Purchasing freshly dug trees that are not hardened-off is not recommended unless you have assurances that they were regularly root pruned during production, have fibrous roots, and the leaves were misted for a week before the sale.
The tree should be installed as soon as possible. It is also critical that the tree be watered twice, immediately after installing, and then watering should be done at least twice a week for the rest of the growing season.
Installing with a pneumatic soil excavating tool (Air-Spade®) or a tree spade may be more successful in the summer than B&B because the root ball can be over-sized and the fine roots are disturbed less.
Winter Planting
Some tree species can be installed when the soil ball is frozen. Large soil balls can be easier to handle and transport with less chance that the ball will crack and damage the roots. Frozen ground provides better access for heavy equipment at both the digging and the installation site. Sugar maple (Acer saccharum), pine (Pinus sp.), honeylocust (Gleditsia triacanthos), elm (Ulmus sp.), linden (Tilia sp.), and crabapple (Malus sp.) are species most suited for winter installation. Red oak (Quercus rubra), dogwood (Cornus florida), hemlock (Tsuga canadensis), sycamore (Platanus occidentalis), sweetgum (Liquidambar styraciflua), birch (Betula sp.), and magnolia (Magnolia sp.) are less likely to survive.
Some nurseries dig trees when the ground is frozen. The frozen surface of the ball replaces the burlap and wire basket. The frozen ball is actually only frozen a few inches around the root ball surface and must not be allowed to thaw out or freeze solid until it is installed. The installation hole must be kept mulched before the tree is installed so the backfill soil is not frozen. This practice requires so much attention to freezing and thawing it is no longer encouraged.
Easily Installed Trees
Scientific name Common name
Abies sp. Fir
Acacia longifolia Acacia
Acer campestre Hedge maple
Acer x freemanii Freeman Maple
Acer miyabei Miyabei Maple
Acer nigrum Black maple
Acer platanoides Norway maple
Acer pseudoplatanus Sycamore maple
Acer rubrum Red maple
Acer saccharinum Silver maple
Acer saccharum Sugar maple
Acer tartaricum Tartaricum Maple
Acer tartaricum ssp. ginnala Amur Maple
Aesculus sp. Buckeye
Aesculus hippocastanum Horsechestnut
Aesculus x carnea Red Horsechestnut
Ailanthus altissima Tree of heaven
Alnus sp Alder
Amelanchier sp. Serviceberry
Casuarina equisetifolia Australian pine
Catalpa sp. Catalpa
Celtis sp. Hackberry
Cercidiphyllum japonicum Katsura tree
Cercis canadensis American redbud
Chionanthus virginicus White fringe tree
Cladrastis kentukea Yellowwood
Clusia rosea Pitch apple
Cocos nucifera Coconut palm
Cornus mas Cornelian cherry Dogwood
Crataegus sp. Hawthorn
Cupaniopsis anacardioides Carrotwood
Elaeagnus angustifolia Russian olive
Fraxinus sp. Ash
Fraxinus quadrangulata Blue ash
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Jacaranda mimosifolia Jacaranda
Juniperus sp. Juniper
Koelreuteria paniculata Goldenraintree
Laburnum x watereri Goldenchain tree
Larix laricina American larch
Liriodendron tulipifera Tulip tree/yellow poplar
Maclura pomifera Osage orange
Malus sp. Apple, crabapple
Morus sp. Mulberry
Paulownia tomentosa Paulownia
Parrotia persica Persian Parrotia
Persea borbonia Redbay
Phellodendron sp. Corktree
Picea abies Norway spruce
Picea glauca White spruce
Picea pungens Colorado spruce
Pinus nigra Austrian pine
Pinus sp. Pine
Platanus sp. Plane tree
Populus sp. Poplar
Prunus 'Accolade' Accolade Flowering Cherry
Prunus sargentii Sargent Cherry
Prunus virginiana 'Canada Red' Chokecherry
Prunus serotina Black cherry
Pseudolarix amabilis Golden larch
Pyrus calleryana Callery pear
Pyrus betulafolia Birchleaf Pear
Pyrus fauriei 'Westwood' Korean Sun Pear
Pyrus ussuriensis Ussarian Pear
Quercus bicolor Swamp White Oak
Quercus imbricaria Shingle oak
Quercus laurifolia Laurel oak
Quercus palustris Pin oak
Quercus phellos Willow oak
Quercus robur English oak
Quercus virginiana Southern live oak
Rhamnus cathartica Common buckthorn
Robinia sp. Black Locust
Sabal palmetto Cabbage palm
Salix sp. Willow
Sorbus sp. Mountain ash
Syringa reticulata Japanese Tree Lilac
Taxus sp. Yew
Thuja occidentalis Arborvitae, white cedar
Tilia sp. Linden, lime
Tsuga sp. Hemlock
Ulmus sp. Elm
Ulmus pumila Siberian elm
Zelkova serrate Zelkova
Two Ways to Successful Installation
Urban trees are now understood to be a central part of green infrastructure systems because they provide a range of benefits. They reduce the urban heat island effect, manage stormwater quality, and provide shade that lengthens the life of pavement materials. In the summer, shadier streets also mean lower neighborhood temperatures, which can reduce utility costs, air pollution, and resident stress. Larger, older trees are far more valuable than younger ones for meeting these benefits, so work needs to be done to preserve older trees and use new techniques to enable younger trees to stay in place longer and grow to maturity. A 30-inch (0.75 m) diameter breast height (dbh) tree provides 70 times the ecological benefits of a 3-inch (7.5 cm) dbh tree.
The key to growing large trees for 50 years or more in a city, is to install them in large amounts of high-quality loamy soil. Installation sites should be large enough to accommodate the tree's roots at maturity. Published research reports indicate four (4) square feet (0.4 sq. m.) of surface area of soil for everyone (1") inch (2.5 cm) of trunk diameter the tree is expected to attain, or two (2) cubic feet (0.05 cu. m.) of soil for every square foot (0.1 sq. m.) of the future crown projection (which is readily available in nursery catalogs as the tree's spread or width). The soil should be about three feet (0.9 m) deep for normal growth and vigor.
If large amounts of high-quality loam are not available, create soil that is 5-15% gravel, 30‐50% sand, 5‐6% silt, at least 5% compost or biochar, and no more than 35% clay. The acceptable range of pH is 5.5 to 7.3. This ideal soil may be applied as a non-compacted amendment to the existing urban soil or better for use as a total soil replacement. Compost and/or biochar should be applied in contact with the roots during installation. This ideal soil is not only the best growing media for urban trees, but it will also filter out excess amounts of heavy metals, nitrogen, and phosphorous from stormwater. Keep in mind that using this soil as an amendment can cause the tree roots to become "pot bound" in the good soil and never venture into the poorer quality urban soil. With this thought in mind, the area being amended should match the area size defined in the paragraph above.
Since a high-quality native soil is not likely in urban sites, the arborist or landscape architect should consider other options. One option should be the selection of a cultivar that has been developed to tolerate urban soils. A second option can be the use of soil cells that suspend the hardscapes (sidewalks, curbs, and streets) at the surface of an underground frame, which prevents soil compaction over the installation pit filled with ideal soil. Recently a third option is becoming popular and uses a variation of CU-Structural Soil®. This option is called the Stockholm Tree Pits. It uses large, crushed stone with soil and biochar washed into the cracks between the stones, that allows tree roots to follow large pores in the stone mix and the stone can be compacted to support the pavement with car and pedestrian traffic at the surface.
Soil Cells
One product called StrataCells, invented in the 1990's and manufactured by CityGreen, look like blocks and are made from 100% polypropylene resin that can be stacked to various heights and cut and shaped as required during construction. They are single component modules that clip together to form a skeletal matrix which is then filled with soil. This makes for a quick and easy installation compared to multiple component alternatives. They can also be spread laterally as wide as necessary including under vehicular traffic and pedestrian areas with minimal surface coverage.
Another similar product is called Silva Cells, produced by DeepRoot. Deep Root soil cells look like steel industrial shelving. The plastic units can be stacked to various heights before they are topped with a deck that supports the pavements at the surface.
The product ArborSystem by GreenBlue, are structural support modules that allow pavements over the proper soil mix used to nourish street trees and have the added benefit of providing stormwater retention.
Other manufacturers have products with names such as the Urban Tree Box and Storm Tank Module. All these units are stacked from a hard surface on the bottom of the installation pit. They are surrounded with the optimum amount of high-quality soil for tree root growth and stormwater treatment. Soil cells can be spread laterally as wide as necessary. Soil cells can also accommodate utilities during installation.
The weight of the paving and any surface loading is transferred downward by the cells to the firm soil at the bottom of the installation pit while the ideal soil remains loose and suitable for root growth. Together, the frame and deck of all the soil cell supports the hardscape and can meet AASHTO H-20 loading requirements. Irrigation systems can be integrated into the soil cell layout. Water can also enter the system through pervious paving, storm drains, and catch basins and pass by plantings to provide water for the trees.
Cons
CU-Structural Soil®
CU-Structural Soil® is marketed by Amereq Inc., a developer of innovative and environmentally compatible hydrogels for horticulture applications, plant nutrients, and bio-stimulants. The CU-Structural Soil® materials are crushed stone, clay loam, and a hydrogel tackifier stabilizing agent. The tackifier is poured over the stone to coat each rock and the loam is then mixed in, to coat the stone. The soil coated stone is then placed in the installation pit where it can be compacted to meet all relevant pavement design requirements. The pavement is installed directly over the compacted CU-Structural Soil®. The CU-Structural Soil® provides voids and soil for tree root growth. The tree roots follow the voids, seeking nutrients from the soil, and water and air from the voids. Water can enter the soil through pervious paving, drains, catch basins, and irrigation systems. If the tree needs to be replaced or utilities need placement or repair, the structural soil can be excavated and replaced using conventional construction equipment.
Patented by Cornell University's Research Foundation, CU-Structural Soil® can safely support pavements and sidewalks and is designed to provide ample rooting area for street trees, thereby decreasing tree mortality and sidewalk failure. It is marketed under the name CU-Structural Soil® or CU-Soil. Properly manufactured and installed CU-Structural Soil® provides an excellent rooting environment with ample air and water movement, nutrient exchange and beneficial biological activity to promote a vigorous life for street trees. CU-Soil is produced by companies across the US, Canada, and the UK who are licensed by Amereq to use tested and approved local material which meets the Cornell University specifications. Using local producers and materials helps to keep the costs down and reduces the carbon footprint. Also, while CU-Structural Soil® will not only aid in filtration, due to its extremely porous nature, it also can act as a stormwater reservoir, slowing the flow of water into the storm drainage system. CU-Structural Soil® is rarely shipped over 100 miles (160 k.) to the installation site, thereby reducing the CO2 emissions released during the installation process.
Cons
Cost Comparison
In an effort to objectively compare these installation concepts in 2011, representatives from Silva Cells, Strata Cells, and CU-Structural Soils® were asked to provide a complete estimate to do a 100 ft. (30 m.) section of a city block where the sidewalk is 10 feet (3 m.) wide with 3 trees being planted in this one section. This section is part of a larger block-long project, so the cost might be related to a typical city project and contractor setup charges are not a factor.
Silva Cells – 670 cu. ft. of soil per tree x 3 trees x $13.42 per cu. ft. of soil (includes excavation, Silva Cells, aggregate base course, soil, geotextile, geogrid, and labor) = $26,974 plus drainage, sidewalk, and trees. Unit prices are based on a project installed in Minneapolis, MN.
StrataCell System – 530 cu. ft. of soil per tree x 3 trees x $9.85 per cubic foot of soil (includes excavation, aggregate base course, StrataCells, geogrid, geotextile, root management materials, aeration/irrigation materials, soil and labor) = $15,661.50
Stratavault System – 423 cu. ft. of soil per tree x 3 trees x $9.78 per cubic foot of soil (includes excavation, aggregate base course, Stratavaults, geogrid, geotextile, root management materials, aeration/irrigation materials, soil and labor) = $12,410.82
CU-Structural Soil® – $50/ton delivered, converted to $65/cubic yard + $14.50(installation cost) = $79.50 per yd installed. The entire project would require 111 cubic yards x $79.50 = $8,825 plus pit excavation, drainage, sidewalk, and trees. Unit prices are based on a 2011 completed project in St. Louis, MO.
Is this expense worth it to a city? City councils may be required to have an asset register detailing the value of assets like roads, parks, etc. In the past, it was hard to quantify the value of trees, but today there are a number of methodologies for doing so. One such method, the Burnley Method – developed by Dr. Greg Moore is now being widely used and accepted in Canada. One city planted several trees in Stratavault soil cells when they were building a parking lot. The trees cost $10,000 each for the tree and soil cell system. Four years later, the trees had grown from a 3 in (75mm) trunk diameter at the time of installation, to 10 in (250mm). Today, these trees are valued at $17,500 each, way more than double the installation cost in 4 years.
As a comparison, the same council had the same species installed several years before these trees and they were growing in a nearby parking lot using the conventional installation method. The lot was paved, so a square cut in the pavement, some curbing placed around the edges, the road base excavated, and soil was loaded into the hole. Planted 15 years ago, these trees are valued at only $510 each today, not quite double the installation cost of $250 per tree.
Conclusion
Recent research has indicated that all the soil cell options listed above grew trees at the same rate except those growing in CU-Soil which grew at a slightly slower rate. All of these installation techniques are more expensive than conventional urban street tree installation, but are also much better. No concept is the end-all panacea for street tree installations. No doubt tree selection and nursery practices are important issues as well.
Note: The mention of brand names in this section does not constitute an endorsement of these products. They are mentioned only for providing the reader with useful and comparative information.
Urban trees are now understood to be a central part of green infrastructure systems because they provide a range of benefits. They reduce the urban heat island effect, manage stormwater quality, and provide shade that lengthens the life of pavement materials. In the summer, shadier streets also mean lower neighborhood temperatures, which can reduce utility costs, air pollution, and resident stress. Larger, older trees are far more valuable than younger ones for meeting these benefits, so work needs to be done to preserve older trees and use new techniques to enable younger trees to stay in place longer and grow to maturity. A 30-inch (0.75 m) diameter breast height (dbh) tree provides 70 times the ecological benefits of a 3-inch (7.5 cm) dbh tree.
The key to growing large trees for 50 years or more in a city, is to install them in large amounts of high-quality loamy soil. Installation sites should be large enough to accommodate the tree's roots at maturity. Published research reports indicate four (4) square feet (0.4 sq. m.) of surface area of soil for everyone (1") inch (2.5 cm) of trunk diameter the tree is expected to attain, or two (2) cubic feet (0.05 cu. m.) of soil for every square foot (0.1 sq. m.) of the future crown projection (which is readily available in nursery catalogs as the tree's spread or width). The soil should be about three feet (0.9 m) deep for normal growth and vigor.
If large amounts of high-quality loam are not available, create soil that is 5-15% gravel, 30‐50% sand, 5‐6% silt, at least 5% compost or biochar, and no more than 35% clay. The acceptable range of pH is 5.5 to 7.3. This ideal soil may be applied as a non-compacted amendment to the existing urban soil or better for use as a total soil replacement. Compost and/or biochar should be applied in contact with the roots during installation. This ideal soil is not only the best growing media for urban trees, but it will also filter out excess amounts of heavy metals, nitrogen, and phosphorous from stormwater. Keep in mind that using this soil as an amendment can cause the tree roots to become "pot bound" in the good soil and never venture into the poorer quality urban soil. With this thought in mind, the area being amended should match the area size defined in the paragraph above.
Since a high-quality native soil is not likely in urban sites, the arborist or landscape architect should consider other options. One option should be the selection of a cultivar that has been developed to tolerate urban soils. A second option can be the use of soil cells that suspend the hardscapes (sidewalks, curbs, and streets) at the surface of an underground frame, which prevents soil compaction over the installation pit filled with ideal soil. Recently a third option is becoming popular and uses a variation of CU-Structural Soil®. This option is called the Stockholm Tree Pits. It uses large, crushed stone with soil and biochar washed into the cracks between the stones, that allows tree roots to follow large pores in the stone mix and the stone can be compacted to support the pavement with car and pedestrian traffic at the surface.
Soil Cells
One product called StrataCells, invented in the 1990's and manufactured by CityGreen, look like blocks and are made from 100% polypropylene resin that can be stacked to various heights and cut and shaped as required during construction. They are single component modules that clip together to form a skeletal matrix which is then filled with soil. This makes for a quick and easy installation compared to multiple component alternatives. They can also be spread laterally as wide as necessary including under vehicular traffic and pedestrian areas with minimal surface coverage.
Another similar product is called Silva Cells, produced by DeepRoot. Deep Root soil cells look like steel industrial shelving. The plastic units can be stacked to various heights before they are topped with a deck that supports the pavements at the surface.
The product ArborSystem by GreenBlue, are structural support modules that allow pavements over the proper soil mix used to nourish street trees and have the added benefit of providing stormwater retention.
Other manufacturers have products with names such as the Urban Tree Box and Storm Tank Module. All these units are stacked from a hard surface on the bottom of the installation pit. They are surrounded with the optimum amount of high-quality soil for tree root growth and stormwater treatment. Soil cells can be spread laterally as wide as necessary. Soil cells can also accommodate utilities during installation.
The weight of the paving and any surface loading is transferred downward by the cells to the firm soil at the bottom of the installation pit while the ideal soil remains loose and suitable for root growth. Together, the frame and deck of all the soil cell supports the hardscape and can meet AASHTO H-20 loading requirements. Irrigation systems can be integrated into the soil cell layout. Water can also enter the system through pervious paving, storm drains, and catch basins and pass by plantings to provide water for the trees.
Cons
- In addition to the carbon dioxide emissions and high cost created from digging the installation pit and hauling in the soil, there are also the emissions released from shipping the cells from their place of manufacture to the installation site.
- The soil cells may be damaged by heavy equipment during the repair or installation of underground utilities. Special attention is required during the layout of the soil cells and the underground utilities.
CU-Structural Soil®
CU-Structural Soil® is marketed by Amereq Inc., a developer of innovative and environmentally compatible hydrogels for horticulture applications, plant nutrients, and bio-stimulants. The CU-Structural Soil® materials are crushed stone, clay loam, and a hydrogel tackifier stabilizing agent. The tackifier is poured over the stone to coat each rock and the loam is then mixed in, to coat the stone. The soil coated stone is then placed in the installation pit where it can be compacted to meet all relevant pavement design requirements. The pavement is installed directly over the compacted CU-Structural Soil®. The CU-Structural Soil® provides voids and soil for tree root growth. The tree roots follow the voids, seeking nutrients from the soil, and water and air from the voids. Water can enter the soil through pervious paving, drains, catch basins, and irrigation systems. If the tree needs to be replaced or utilities need placement or repair, the structural soil can be excavated and replaced using conventional construction equipment.
Patented by Cornell University's Research Foundation, CU-Structural Soil® can safely support pavements and sidewalks and is designed to provide ample rooting area for street trees, thereby decreasing tree mortality and sidewalk failure. It is marketed under the name CU-Structural Soil® or CU-Soil. Properly manufactured and installed CU-Structural Soil® provides an excellent rooting environment with ample air and water movement, nutrient exchange and beneficial biological activity to promote a vigorous life for street trees. CU-Soil is produced by companies across the US, Canada, and the UK who are licensed by Amereq to use tested and approved local material which meets the Cornell University specifications. Using local producers and materials helps to keep the costs down and reduces the carbon footprint. Also, while CU-Structural Soil® will not only aid in filtration, due to its extremely porous nature, it also can act as a stormwater reservoir, slowing the flow of water into the storm drainage system. CU-Structural Soil® is rarely shipped over 100 miles (160 k.) to the installation site, thereby reducing the CO2 emissions released during the installation process.
Cons
- Just like the soil cells, emissions and high cost will be created from digging the installation pit, as well as hauling and mixing the stone.
Cost Comparison
In an effort to objectively compare these installation concepts in 2011, representatives from Silva Cells, Strata Cells, and CU-Structural Soils® were asked to provide a complete estimate to do a 100 ft. (30 m.) section of a city block where the sidewalk is 10 feet (3 m.) wide with 3 trees being planted in this one section. This section is part of a larger block-long project, so the cost might be related to a typical city project and contractor setup charges are not a factor.
Silva Cells – 670 cu. ft. of soil per tree x 3 trees x $13.42 per cu. ft. of soil (includes excavation, Silva Cells, aggregate base course, soil, geotextile, geogrid, and labor) = $26,974 plus drainage, sidewalk, and trees. Unit prices are based on a project installed in Minneapolis, MN.
StrataCell System – 530 cu. ft. of soil per tree x 3 trees x $9.85 per cubic foot of soil (includes excavation, aggregate base course, StrataCells, geogrid, geotextile, root management materials, aeration/irrigation materials, soil and labor) = $15,661.50
Stratavault System – 423 cu. ft. of soil per tree x 3 trees x $9.78 per cubic foot of soil (includes excavation, aggregate base course, Stratavaults, geogrid, geotextile, root management materials, aeration/irrigation materials, soil and labor) = $12,410.82
CU-Structural Soil® – $50/ton delivered, converted to $65/cubic yard + $14.50(installation cost) = $79.50 per yd installed. The entire project would require 111 cubic yards x $79.50 = $8,825 plus pit excavation, drainage, sidewalk, and trees. Unit prices are based on a 2011 completed project in St. Louis, MO.
Is this expense worth it to a city? City councils may be required to have an asset register detailing the value of assets like roads, parks, etc. In the past, it was hard to quantify the value of trees, but today there are a number of methodologies for doing so. One such method, the Burnley Method – developed by Dr. Greg Moore is now being widely used and accepted in Canada. One city planted several trees in Stratavault soil cells when they were building a parking lot. The trees cost $10,000 each for the tree and soil cell system. Four years later, the trees had grown from a 3 in (75mm) trunk diameter at the time of installation, to 10 in (250mm). Today, these trees are valued at $17,500 each, way more than double the installation cost in 4 years.
As a comparison, the same council had the same species installed several years before these trees and they were growing in a nearby parking lot using the conventional installation method. The lot was paved, so a square cut in the pavement, some curbing placed around the edges, the road base excavated, and soil was loaded into the hole. Planted 15 years ago, these trees are valued at only $510 each today, not quite double the installation cost of $250 per tree.
Conclusion
Recent research has indicated that all the soil cell options listed above grew trees at the same rate except those growing in CU-Soil which grew at a slightly slower rate. All of these installation techniques are more expensive than conventional urban street tree installation, but are also much better. No concept is the end-all panacea for street tree installations. No doubt tree selection and nursery practices are important issues as well.
Note: The mention of brand names in this section does not constitute an endorsement of these products. They are mentioned only for providing the reader with useful and comparative information.
Tree Installation Pits & Above Ground Containers
Sometimes called “tree vaults,” tree installation pits are also referred to as “tree coffins,” and with good reason. Trees in concrete-laden urban settings and surrounded by concrete sidewalks struggle with many stresses that inhibit growth such as limited rooting space, air pollution, road salt, excessive temperature, vehicle impacts, etc. Although installing trees in tree pits are not ideal, in many cases pits offer the only opportunity for installing trees in a street-scape setting. Tree pits should be constructed so that a continuous channel of soil under the pavement connects the individual pits and which provide greater volumes of soil for shared root growth and water storage. Raised tree pits can likewise be designed to accommodate multiple rather than single trees.
Where individual pits must be constructed, they can either be above, at, or below the surface of the pavement. If they are above, extra provisions must be made for supplemental fertilization and irrigation. If they are at surface level, plant some tough hardy perennials or ground covers at the time of tree installation to discourage foot traffic over the tree roots. If the tree pit's soil level will be 2” – 8” below the pavement surface, install concrete pavers, an adjustable pit cover, or grate to accommodate trunk growth and avoid a pedestrian accident. For more information on planting a perennial groundcover, see this article about Living Mulch.
Rooting Space
Unfortunately, planting success in a tree pit often follows what might be called the “Rule of Four”: the roots of a tree with a 4” trunk diameter will fill up a 4’x4’x4’ pit within 4 years. This usually results in a growth slowdown or stoppage and premature tree death. A planned street or sidewalk reconstruction offers a prime opportunity to build better tree installation sites. There should be at least 5 cubic feet of soil per 1 square foot of crown spread at maturity. The following strategies are the best bets for ensuring tree survival and green streets.
Good Soil
The best method to prepare a pit for tree installation is to remove all urban rubble and refill as much soil around the tree pit area as possible with uniform, good quality loam, following the specification recommended in this website. Soil ingredients should be thoroughly prepared and mixed before installation, according to the information in the section above. The soil type should be consistent throughout the pit and to the outermost location available for root growth. Soils for tree pit design must carefully fit the location. Aeration and water – too much or too little, must be considered.
The CU-Structural Soil mix, as mentioned above, is sometimes called an engineered or load-bearing soil, and is an alternative for installation in pits and under sidewalks. For more information about CU-Soil, also see Topic #3.
Amsterdam Tree Soil is another soil mix that will hold water for the tree while allowing for the modest compaction necessary for sidewalks. Unfortunately, the compaction rate of 80% is not acceptable by code, in most cities within the United States. More information on Amsterdam Tree Soil is also available in Topic #3.
Water
A tree in a pit often suffers from oxygen deprivation due to poor drainage. In addition to filling the pit with a uniform soil profile, drainage can be facilitated by a system that will drain excess water from the roots. The wells can be linked with a network of perforated pipes running from storm drains to the tree. Below the tree roots a second drain with perforated pipe should connect to the city's storm drain. This system not only provides ample water for the tree, but the water passing through the soil is cleaned and it returns to the storm drainage system, much cleaner than it was on the street.
The typical tree pit has a volume of only 64 cubic feet for root space. Research has shown that a tree with a 20’ diameter canopy requires 300 cubic feet to have enough water for ten days without rain. Trees in pits should be deeply watered two or three times during backfilling and deep, regular soakings thereafter. The use of permeable pavers instead of solid concrete walks can be another way to enable water and oxygen to permeate the soil in the tree pit.
Citizen volunteers concerned with street tree survival are using an innovative irrigation system in Boston, MA. Used in conjunction with a tree grate, the system consists of a 4” black perforated pipe inside a filter sleeve to keep out silt; a “T” joint; and a 4” round black slotted drain cap. The perforated pipe is laid in a circle just below the soil surface around the root ball, with the “T” joint leading up to the drain cap. Although the cap is protected beneath the grate, it is easily accessible with a hose. Boston’s tree advocate groups now only install a tree when they have a volunteer committed to watering it. Once a week the volunteer uses a hose to fill the system to overflowing, lets it drain, and then fills it again. The entire system costs about $10 per tree, and it holds up for about three years, long enough to get the young tree established.
Plastic irrigator bags are commercially available products that drain very slowly, so as to provide an effectively deep watering of young trees. A number of communities have had success with these and most report that vandalism has not been a problem despite the visibility of the bags. A scheduled maintenance commitment is necessary to ensure that the bags are filled regularly. Each bag can be filled in a couple of minutes as opposed to conventional watering that will take 15 to 30 minutes.
Newly installed trees benefit from:
Choose the Right Species
A critical step toward the creation of any sustainable street-scape is to select the right tree for the right place. Only small trees or flood plain species can survive in small spaces like the typical tree pit. Installing trees in self-contained tree pits dictates the use of slow-growing species that have a relatively small mature size and a tolerance for urban conditions. Near utilities and other structures, trees with a columnar shape can avoid pruning later.
Tree Grates
A tree grate serves as a sidewalk-like surface for pedestrian traffic, protecting the soil from compaction and still enabling water to reach the roots. Tree grates have fallen out of favor for street tree installations because the concentric rings of the grates are seldom cut away as the tree trunk grows in diameter. Eventually the grate girdles the trunk and the tree meets an untimely early death.
Tree Grate Standards
Tree grates are available in standard sizes in round, square, or rectangular shapes. The designs are ADA (American with Disabilities Act) compliant with openings no greater than ¼” (0.6cm) and are easily modified to accept up-lighting. An annual maintenance visit must be included in the budget before the tree is installed. This visit will provide for expanding the grate opening to not restrict the growth of the trunk diameter.
The two most common mistakes when specifying tree grates are choosing inappropriate sizes and improper installation. If a tree grate is placed directly on the soil instead of suspended on a proper frame, it may cause soil compaction, a potential trip hazard, and vertical compression on the roots that will destroy a tree completely. Use tree grates with a minimum 12” (30 cm) opening for the tree and with removable sections that can be broken or cut out to allow for the growth of the tree. Fill the space between the finish grade of the tree and the tree grate with gravel larger than ¼” (0.6cm) to limit the accumulation of debris under the grate while still allowing air and water penetration.
Tree Guards
Tree guards should extend vertically from tree grates and serve to protect trees in highly active areas. Tree guards should be narrow bars painted in a similar color, and related to other site furnishings. If they are custom made, consideration should be given to making them large enough to protect the tree in a 4' by 4' (1.3 x1.3 m) sidewalk cutout. They are designed to protect trees from sidewalk maintenance, vandals, and animals. They are manufactured in two or more pieces and are bolted together for ease of shipping and installation around the trees. The tree guards should be removed as soon as the tree trunk is large enough to be seen by sidewalk snow plow operators and large enough to tolerate bicycles chained to the trunk.
Pavers
Instead of tree grates, bricks, and cobblestones, pavers can be used to create a low-walled area surrounding the planting pit that is 6” – 12” (15 – 30 cm) above sidewalk level. This raised bed encourages pedestrians to walk around and helps limit compaction over the roots closest to the tree. Since this raised area might be considered a tripping hazard, an option is to lay unit pavers level with the sidewalk around the tree. Pavers allow air and water to move into the soil through the cracks between the pavers. Pavers are most effective when used in conjunction with structural soils or soil cells, avoiding the need for a heavily compacted base of stone dust or sand.
Another option to consider is the use of living mulches, otherwise known as planting perennials or groundcovers. People will seldom walk on the flowering plants, thereby preventing soil compaction. When the plants are installed soon after the tree is installed, the plants will use the same water as applied to the tree. In locations where there is winter snow, evergreen groundcovers are visible, year-round.
Mulch
Organic mulch is normally recommended around trees for water retention and weed prevention. However, it is impractical for street trees set level with sidewalks. Mulch may be used in a raised planting bed if the sides are high enough to contain it or fenced off to keep pedestrians from walking on the mulch or tripping on the fence.
Structural Pruning
The pruning goal for a pit-bound tree is to keep it at a manageable size that will help it maintain a sustainable shoot-to-root ratio. One tip is to order the tree from the nursery as unpruned. By not pruning the lowest branches on the tree. They will discourage people from walking too close to the tree and they are easily removed as the tree grows. The other option is to install low branching evergreens.
Maintenance
Maintenance on newly installed trees should be planned for at least one year after installation and preferably into the second and third years. Volunteers can be great assistants for watering and for training young trees with structural pruning from the ground. Volunteers are enthusiastic, often protective advocates for public trees, and they are cost-effective labor. However, the volunteers must receive a day of training and trimming practice before they are assigned to structural pruning on city trees. Structural pruning usually begins two years after installation. See Topic #17 for more information about pruning.
In many communities, an installation in a planting well is one of the primary opportunities to grow trees in the city. Even though pits are not perfect, sound installation and maintenance practices can go a long way toward compensating for the limiting site factors that they present.
Above Ground Containers
Above ground containers that are decorative and sit on top of a paved surface, come in a wide range of sizes, colors, and materials. The sizes for trees range from 90 gallons (44” diameter by 18” high) up to 450 gallons (70” diameter by 30” high) [340 liters (110 cm dia. x 48 cm high) to 1700 liters (180 cm dia. x 75 cm high)]. They can be made of wood, a variety of plastics and metals, ceramic, stone, and precast concrete. They are built for street tree use, as well as for buildings, homes, and offices. They are used indoors as well as outdoors in areas where they have the most visual impacts.
Always install the right type of tree in the container that would fit its root system. Be sure that the container offers ample soil support and water retention. Plants need to be continually watered in containers and drain holes are necessary to remove any excess water. Container planting means constant watering especially in hot dry spells.
Self-watering planters are recommended because they have a reservoir with a hose-fill attachment. By keeping the reservoir filled, the plants will not run out of water. The design provides continuous soak utilizing capillary action through perforations that expose the soil to the water reservoir. If there are heavy rains, the planters should have built in overflows to eliminate over-watering.
Small Stature Trees for Small Installation Sites
Hedge Maple
Amur Maple
Japanese Maple
Karpick Red Maple
Cumulus Shadblow
Robin Hill Shadblow
Pink Shadblow
American Redbud
White flowering Dogwood
Kousa Dogwood
Cornelian Cherry
Tea Crabapple
Van Eseltine Crabapple
Redbud Crabapple
Sourwood
Amanogawa Cherry
Japanese Tee Lilac
Summer Snow Japanese Tree Lilac
Sometimes called “tree vaults,” tree installation pits are also referred to as “tree coffins,” and with good reason. Trees in concrete-laden urban settings and surrounded by concrete sidewalks struggle with many stresses that inhibit growth such as limited rooting space, air pollution, road salt, excessive temperature, vehicle impacts, etc. Although installing trees in tree pits are not ideal, in many cases pits offer the only opportunity for installing trees in a street-scape setting. Tree pits should be constructed so that a continuous channel of soil under the pavement connects the individual pits and which provide greater volumes of soil for shared root growth and water storage. Raised tree pits can likewise be designed to accommodate multiple rather than single trees.
Where individual pits must be constructed, they can either be above, at, or below the surface of the pavement. If they are above, extra provisions must be made for supplemental fertilization and irrigation. If they are at surface level, plant some tough hardy perennials or ground covers at the time of tree installation to discourage foot traffic over the tree roots. If the tree pit's soil level will be 2” – 8” below the pavement surface, install concrete pavers, an adjustable pit cover, or grate to accommodate trunk growth and avoid a pedestrian accident. For more information on planting a perennial groundcover, see this article about Living Mulch.
Rooting Space
Unfortunately, planting success in a tree pit often follows what might be called the “Rule of Four”: the roots of a tree with a 4” trunk diameter will fill up a 4’x4’x4’ pit within 4 years. This usually results in a growth slowdown or stoppage and premature tree death. A planned street or sidewalk reconstruction offers a prime opportunity to build better tree installation sites. There should be at least 5 cubic feet of soil per 1 square foot of crown spread at maturity. The following strategies are the best bets for ensuring tree survival and green streets.
Good Soil
The best method to prepare a pit for tree installation is to remove all urban rubble and refill as much soil around the tree pit area as possible with uniform, good quality loam, following the specification recommended in this website. Soil ingredients should be thoroughly prepared and mixed before installation, according to the information in the section above. The soil type should be consistent throughout the pit and to the outermost location available for root growth. Soils for tree pit design must carefully fit the location. Aeration and water – too much or too little, must be considered.
The CU-Structural Soil mix, as mentioned above, is sometimes called an engineered or load-bearing soil, and is an alternative for installation in pits and under sidewalks. For more information about CU-Soil, also see Topic #3.
Amsterdam Tree Soil is another soil mix that will hold water for the tree while allowing for the modest compaction necessary for sidewalks. Unfortunately, the compaction rate of 80% is not acceptable by code, in most cities within the United States. More information on Amsterdam Tree Soil is also available in Topic #3.
Water
A tree in a pit often suffers from oxygen deprivation due to poor drainage. In addition to filling the pit with a uniform soil profile, drainage can be facilitated by a system that will drain excess water from the roots. The wells can be linked with a network of perforated pipes running from storm drains to the tree. Below the tree roots a second drain with perforated pipe should connect to the city's storm drain. This system not only provides ample water for the tree, but the water passing through the soil is cleaned and it returns to the storm drainage system, much cleaner than it was on the street.
The typical tree pit has a volume of only 64 cubic feet for root space. Research has shown that a tree with a 20’ diameter canopy requires 300 cubic feet to have enough water for ten days without rain. Trees in pits should be deeply watered two or three times during backfilling and deep, regular soakings thereafter. The use of permeable pavers instead of solid concrete walks can be another way to enable water and oxygen to permeate the soil in the tree pit.
Citizen volunteers concerned with street tree survival are using an innovative irrigation system in Boston, MA. Used in conjunction with a tree grate, the system consists of a 4” black perforated pipe inside a filter sleeve to keep out silt; a “T” joint; and a 4” round black slotted drain cap. The perforated pipe is laid in a circle just below the soil surface around the root ball, with the “T” joint leading up to the drain cap. Although the cap is protected beneath the grate, it is easily accessible with a hose. Boston’s tree advocate groups now only install a tree when they have a volunteer committed to watering it. Once a week the volunteer uses a hose to fill the system to overflowing, lets it drain, and then fills it again. The entire system costs about $10 per tree, and it holds up for about three years, long enough to get the young tree established.
Plastic irrigator bags are commercially available products that drain very slowly, so as to provide an effectively deep watering of young trees. A number of communities have had success with these and most report that vandalism has not been a problem despite the visibility of the bags. A scheduled maintenance commitment is necessary to ensure that the bags are filled regularly. Each bag can be filled in a couple of minutes as opposed to conventional watering that will take 15 to 30 minutes.
Newly installed trees benefit from:
- daily watering for the first one to two weeks, applying approximately 1.5 gallons per caliper inch (1.5 liters per caliper centimeter) per watering.
- after two weeks, water the trees every two to three days for the next two or three months, with approximately 1.5 gallons per caliper inch (1.5 liters per caliper cm).
- after 2-3 months, weekly watering is necessary for the remainder of the season or until the tree is established.
- after the first year, if watering is necessary, it should be 1 gallon of water per inch of caliper. This equates to 1 inch of rainfall per week.
Choose the Right Species
A critical step toward the creation of any sustainable street-scape is to select the right tree for the right place. Only small trees or flood plain species can survive in small spaces like the typical tree pit. Installing trees in self-contained tree pits dictates the use of slow-growing species that have a relatively small mature size and a tolerance for urban conditions. Near utilities and other structures, trees with a columnar shape can avoid pruning later.
Tree Grates
A tree grate serves as a sidewalk-like surface for pedestrian traffic, protecting the soil from compaction and still enabling water to reach the roots. Tree grates have fallen out of favor for street tree installations because the concentric rings of the grates are seldom cut away as the tree trunk grows in diameter. Eventually the grate girdles the trunk and the tree meets an untimely early death.
Tree Grate Standards
Tree grates are available in standard sizes in round, square, or rectangular shapes. The designs are ADA (American with Disabilities Act) compliant with openings no greater than ¼” (0.6cm) and are easily modified to accept up-lighting. An annual maintenance visit must be included in the budget before the tree is installed. This visit will provide for expanding the grate opening to not restrict the growth of the trunk diameter.
The two most common mistakes when specifying tree grates are choosing inappropriate sizes and improper installation. If a tree grate is placed directly on the soil instead of suspended on a proper frame, it may cause soil compaction, a potential trip hazard, and vertical compression on the roots that will destroy a tree completely. Use tree grates with a minimum 12” (30 cm) opening for the tree and with removable sections that can be broken or cut out to allow for the growth of the tree. Fill the space between the finish grade of the tree and the tree grate with gravel larger than ¼” (0.6cm) to limit the accumulation of debris under the grate while still allowing air and water penetration.
Tree Guards
Tree guards should extend vertically from tree grates and serve to protect trees in highly active areas. Tree guards should be narrow bars painted in a similar color, and related to other site furnishings. If they are custom made, consideration should be given to making them large enough to protect the tree in a 4' by 4' (1.3 x1.3 m) sidewalk cutout. They are designed to protect trees from sidewalk maintenance, vandals, and animals. They are manufactured in two or more pieces and are bolted together for ease of shipping and installation around the trees. The tree guards should be removed as soon as the tree trunk is large enough to be seen by sidewalk snow plow operators and large enough to tolerate bicycles chained to the trunk.
Pavers
Instead of tree grates, bricks, and cobblestones, pavers can be used to create a low-walled area surrounding the planting pit that is 6” – 12” (15 – 30 cm) above sidewalk level. This raised bed encourages pedestrians to walk around and helps limit compaction over the roots closest to the tree. Since this raised area might be considered a tripping hazard, an option is to lay unit pavers level with the sidewalk around the tree. Pavers allow air and water to move into the soil through the cracks between the pavers. Pavers are most effective when used in conjunction with structural soils or soil cells, avoiding the need for a heavily compacted base of stone dust or sand.
Another option to consider is the use of living mulches, otherwise known as planting perennials or groundcovers. People will seldom walk on the flowering plants, thereby preventing soil compaction. When the plants are installed soon after the tree is installed, the plants will use the same water as applied to the tree. In locations where there is winter snow, evergreen groundcovers are visible, year-round.
Mulch
Organic mulch is normally recommended around trees for water retention and weed prevention. However, it is impractical for street trees set level with sidewalks. Mulch may be used in a raised planting bed if the sides are high enough to contain it or fenced off to keep pedestrians from walking on the mulch or tripping on the fence.
Structural Pruning
The pruning goal for a pit-bound tree is to keep it at a manageable size that will help it maintain a sustainable shoot-to-root ratio. One tip is to order the tree from the nursery as unpruned. By not pruning the lowest branches on the tree. They will discourage people from walking too close to the tree and they are easily removed as the tree grows. The other option is to install low branching evergreens.
Maintenance
Maintenance on newly installed trees should be planned for at least one year after installation and preferably into the second and third years. Volunteers can be great assistants for watering and for training young trees with structural pruning from the ground. Volunteers are enthusiastic, often protective advocates for public trees, and they are cost-effective labor. However, the volunteers must receive a day of training and trimming practice before they are assigned to structural pruning on city trees. Structural pruning usually begins two years after installation. See Topic #17 for more information about pruning.
In many communities, an installation in a planting well is one of the primary opportunities to grow trees in the city. Even though pits are not perfect, sound installation and maintenance practices can go a long way toward compensating for the limiting site factors that they present.
Above Ground Containers
Above ground containers that are decorative and sit on top of a paved surface, come in a wide range of sizes, colors, and materials. The sizes for trees range from 90 gallons (44” diameter by 18” high) up to 450 gallons (70” diameter by 30” high) [340 liters (110 cm dia. x 48 cm high) to 1700 liters (180 cm dia. x 75 cm high)]. They can be made of wood, a variety of plastics and metals, ceramic, stone, and precast concrete. They are built for street tree use, as well as for buildings, homes, and offices. They are used indoors as well as outdoors in areas where they have the most visual impacts.
Always install the right type of tree in the container that would fit its root system. Be sure that the container offers ample soil support and water retention. Plants need to be continually watered in containers and drain holes are necessary to remove any excess water. Container planting means constant watering especially in hot dry spells.
Self-watering planters are recommended because they have a reservoir with a hose-fill attachment. By keeping the reservoir filled, the plants will not run out of water. The design provides continuous soak utilizing capillary action through perforations that expose the soil to the water reservoir. If there are heavy rains, the planters should have built in overflows to eliminate over-watering.
Small Stature Trees for Small Installation Sites
Hedge Maple
Amur Maple
Japanese Maple
Karpick Red Maple
Cumulus Shadblow
Robin Hill Shadblow
Pink Shadblow
American Redbud
White flowering Dogwood
Kousa Dogwood
Cornelian Cherry
Tea Crabapple
Van Eseltine Crabapple
Redbud Crabapple
Sourwood
Amanogawa Cherry
Japanese Tee Lilac
Summer Snow Japanese Tree Lilac
Training Young Trees
Training young trees refers to a pruning method meant to establish good form and improve branch structure at an early age. In general, the smaller the wound and the younger the tree, the less decay will result. Properly trained trees are not only more aesthetically pleasing, but are structurally stronger. This can significantly reduce the likelihood of branch or trunk failure as the tree matures and the need for corrective pruning and other maintenance measures over time. This means a longer life span for the tree and a better return on your investment. This pruning should begin two years after installing the tree.
The belief that trees should be pruned when installed to compensate for root loss is misguided and proven to be a bad practice. Trees need all their leaves and shoot tips to provide food and the substances that stimulate new root production. Unpruned trees establish much faster and with a stronger root system than trees pruned at the time of installation.
Proper Pruning
Pruning trees when they are young will eliminate long-term problems. Co-dominant stems are a prime example. By removing a leader when the tree is very young, the tree can easily recover and the wound is very small. Pruning young trees will also reduce potential damage from hazards and improve a tree's sustained strength to reduce failure. Multiple branches arising from the same point on the stem are weak attachments and should be removed early.
When a tree has been recently installed, it is in severe stress. This stress will often cause the tree to send out co-dominate stems that become visible within a year or two after installation. One of these stems must be cut off or reduced in size so that the entire tree is not subject to failure in the future.
The growth habit of the tree and its landscape use determine how and to what extent you must prune it to train it to the desired form. Trees with a strong central leader and a conical shape like Sweet Gum (Liquidambar) and pin oak (Quercus palustris) may need little or no pruning. Conifers can develop co-dominant stems that should be removed early and during their dormant period. Sugar maples (Acer saccharum) often produce multiple leaders and need quite a bit of early pruning. On the other hand, trees with irregular growth habits like Chinese pistache (Pistacia chinensis), with poor branch structure like Modesto ash (Fraxinus velutina), or with vigorous laterals as in flowering fruit trees, may need considerable training. Street trees should have higher scaffold branches than trees used for visual screening or windbreaks. Pruning is usually the most effective way to direct the growth of a plant.
Five Step Program
A five-step program has been developed to properly prune a young tree. To reduce the stress on newly installed trees, training should not begin until 3 years after planting, when re-mulching can also be done. Newly installed trees could receive Steps 1 and 2 once the roots are established.
Step 1
At planting time, inspect the tree and remove dead and diseased branches only. Broken or damaged branches provide an entry point for insects, rot, and diseases. Pruning off diseased branches can often prevent the infection from spreading to other parts of the tree.
Step 2
Select a central leader and remove competing branches. Two years after installation, most tree species benefit from having one central stem that tapers to a single leader at the top of the crown. If there are multiple leaders competing with each other, select the most vigorous and vertically oriented, and then remove the rest. Don’t worry if the leader selected is not perfectly straight or vertical, as this will usually self-correct as the tree grows. Also note that multiple leaders begin in response to the stress of installation so they are not visible in Step 1.
Step 3
Select the lowest permanent branch depending on the intended use of the tree. Check local ordinances for minimum branch height mandates. For example, street trees should be pruned so the lowest branch on the sidewalk side is at eight feet (8') (2.4 m) from the ground and the lowest branch on the street side is at fourteen feet (14')(4.5 m). Strong attachments should also be preserved and weak attachments should be removed. In areas that require higher minimum branch heights, it may be necessary to wait until the tree grows taller before determining the lowest branch.
Step 4
Select scaffold branches above the lowest prominent branch and cut back or remove competing branches. Select strong attachments and check radial spacing and vertical spacing. Scaffold branches are those that will remain permanent and will dictate the overall form of the tree. All scaffold branches should share a strong union with the main stem, and their maximum diameter (thickness) should be no more than ½ the diameter of the trunk at the point of attachment. All weakly joined branches should be removed or cut back significantly to direct growth to scaffold branches. Vertical spacing between scaffold branches should be roughly eighteen inches (18")(48 cm) for large trees (mature trunk diameter 12”+)(30 cm+) and twelve inches (12")(30 cm) for smaller trees. As the tree matures, it may be necessary to prune and/or remove some of the original scaffold branches. Two or more vigorous branches arising at or near the same level on the trunk are apt to "choke" the leader and branches above. This is especially true in "fast-growing" trees whose laterals grow from buds formed the previous season, such as flowering fruit trees, mulberry (Morus), and Zelkova.
Step 5
Temporary branches should be selected and retained for several years. These are branches below the lowest permanent branch. Leaving several temporary branches will help to maintain diameter growth in the lower part of the trunk. The leaves on temporary branches produce food for the young tree, protect the young bark from the sun, and they can be removed later when shaded out. Temporary branches should be smaller and less vigorous than the permanent scaffold branches to avoid competition. It may also be useful to prune temporary branches back to the third bud to minimize competition. Doing so serves to increase stem taper, providing the tree with a base that is more stable under high winds and heavy loads of snow and ice. Branches on the lower stem can also help reduce vandalism and other mechanical injuries. When the trunks of small growing trees (e.g. crape myrtle and Japanese maple) are two to three inches (2" – 3") in caliper, or large trees (e.g. elm and sycamore) are five to six inches (5" – 6") in caliper, the number of temporary branches can be reduced over a 1, 2, and 3 year period. Remove the largest ones at each pruning to minimize the size of the pruning wounds.
Helpful Tips
Training young trees refers to a pruning method meant to establish good form and improve branch structure at an early age. In general, the smaller the wound and the younger the tree, the less decay will result. Properly trained trees are not only more aesthetically pleasing, but are structurally stronger. This can significantly reduce the likelihood of branch or trunk failure as the tree matures and the need for corrective pruning and other maintenance measures over time. This means a longer life span for the tree and a better return on your investment. This pruning should begin two years after installing the tree.
The belief that trees should be pruned when installed to compensate for root loss is misguided and proven to be a bad practice. Trees need all their leaves and shoot tips to provide food and the substances that stimulate new root production. Unpruned trees establish much faster and with a stronger root system than trees pruned at the time of installation.
Proper Pruning
Pruning trees when they are young will eliminate long-term problems. Co-dominant stems are a prime example. By removing a leader when the tree is very young, the tree can easily recover and the wound is very small. Pruning young trees will also reduce potential damage from hazards and improve a tree's sustained strength to reduce failure. Multiple branches arising from the same point on the stem are weak attachments and should be removed early.
When a tree has been recently installed, it is in severe stress. This stress will often cause the tree to send out co-dominate stems that become visible within a year or two after installation. One of these stems must be cut off or reduced in size so that the entire tree is not subject to failure in the future.
The growth habit of the tree and its landscape use determine how and to what extent you must prune it to train it to the desired form. Trees with a strong central leader and a conical shape like Sweet Gum (Liquidambar) and pin oak (Quercus palustris) may need little or no pruning. Conifers can develop co-dominant stems that should be removed early and during their dormant period. Sugar maples (Acer saccharum) often produce multiple leaders and need quite a bit of early pruning. On the other hand, trees with irregular growth habits like Chinese pistache (Pistacia chinensis), with poor branch structure like Modesto ash (Fraxinus velutina), or with vigorous laterals as in flowering fruit trees, may need considerable training. Street trees should have higher scaffold branches than trees used for visual screening or windbreaks. Pruning is usually the most effective way to direct the growth of a plant.
Five Step Program
A five-step program has been developed to properly prune a young tree. To reduce the stress on newly installed trees, training should not begin until 3 years after planting, when re-mulching can also be done. Newly installed trees could receive Steps 1 and 2 once the roots are established.
Step 1
At planting time, inspect the tree and remove dead and diseased branches only. Broken or damaged branches provide an entry point for insects, rot, and diseases. Pruning off diseased branches can often prevent the infection from spreading to other parts of the tree.
Step 2
Select a central leader and remove competing branches. Two years after installation, most tree species benefit from having one central stem that tapers to a single leader at the top of the crown. If there are multiple leaders competing with each other, select the most vigorous and vertically oriented, and then remove the rest. Don’t worry if the leader selected is not perfectly straight or vertical, as this will usually self-correct as the tree grows. Also note that multiple leaders begin in response to the stress of installation so they are not visible in Step 1.
Step 3
Select the lowest permanent branch depending on the intended use of the tree. Check local ordinances for minimum branch height mandates. For example, street trees should be pruned so the lowest branch on the sidewalk side is at eight feet (8') (2.4 m) from the ground and the lowest branch on the street side is at fourteen feet (14')(4.5 m). Strong attachments should also be preserved and weak attachments should be removed. In areas that require higher minimum branch heights, it may be necessary to wait until the tree grows taller before determining the lowest branch.
Step 4
Select scaffold branches above the lowest prominent branch and cut back or remove competing branches. Select strong attachments and check radial spacing and vertical spacing. Scaffold branches are those that will remain permanent and will dictate the overall form of the tree. All scaffold branches should share a strong union with the main stem, and their maximum diameter (thickness) should be no more than ½ the diameter of the trunk at the point of attachment. All weakly joined branches should be removed or cut back significantly to direct growth to scaffold branches. Vertical spacing between scaffold branches should be roughly eighteen inches (18")(48 cm) for large trees (mature trunk diameter 12”+)(30 cm+) and twelve inches (12")(30 cm) for smaller trees. As the tree matures, it may be necessary to prune and/or remove some of the original scaffold branches. Two or more vigorous branches arising at or near the same level on the trunk are apt to "choke" the leader and branches above. This is especially true in "fast-growing" trees whose laterals grow from buds formed the previous season, such as flowering fruit trees, mulberry (Morus), and Zelkova.
Step 5
Temporary branches should be selected and retained for several years. These are branches below the lowest permanent branch. Leaving several temporary branches will help to maintain diameter growth in the lower part of the trunk. The leaves on temporary branches produce food for the young tree, protect the young bark from the sun, and they can be removed later when shaded out. Temporary branches should be smaller and less vigorous than the permanent scaffold branches to avoid competition. It may also be useful to prune temporary branches back to the third bud to minimize competition. Doing so serves to increase stem taper, providing the tree with a base that is more stable under high winds and heavy loads of snow and ice. Branches on the lower stem can also help reduce vandalism and other mechanical injuries. When the trunks of small growing trees (e.g. crape myrtle and Japanese maple) are two to three inches (2" – 3") in caliper, or large trees (e.g. elm and sycamore) are five to six inches (5" – 6") in caliper, the number of temporary branches can be reduced over a 1, 2, and 3 year period. Remove the largest ones at each pruning to minimize the size of the pruning wounds.
Helpful Tips
- As a general rule, no more than 25% of the living crown should be removed in one year. Large defective branches or exceptionally vigorous trees may warrant more aggressive pruning.
- Roughly half of the foliage should be on branches originating from the lower 2/3 of the main stem. This rule can be useful in guiding your selection of permanent branches.
- Prune during the winter months while trees are dormant, though badly re-sprouting species such as
lindens or crabapples are better pruned soon after leaves have fully expanded. Branches that are dead, diseased, or damaged can be removed anytime.
- Using proper pruning techniques is essential. Poor pruning can cause damage that lasts for the life of the tree.
- Weak young trees may result from a number of unfavorable growing conditions, either in the nursery or after installing in the landscape. If such problems as girdling or kinked roots, disease, insects, trunk sunburn, poorly drained soil, etc. are not limiting growth, severe pruning may be the last resort that will revitalize the tree.
Trees that Tolerate Urban Environments
Listed below are this author's opinion of trees that tolerate urban environmental conditions. These trees will tolerate poor soil, poor air quality, and uneven watering. They should do well in our cities, along the streets, and on public properties. Although installing trees in sidewalk openings are not the best sites for growing trees, if there are no other options, the following trees should survive and grow reasonably well. Admittedly, trees such as the silver maple, boxelder, and tree of heaven should never be used in a city, but if you have the space and need a tree where nothing else will grow, then use them. The trees listed here will be suitable for USDA Hardiness Zones 3 – 10.
Scientific name Common name
Acacia retinodes Acacia
Acer campestre Hedge maple
Acer x freemanii Freeman maple
Acer miyabei Miyabe maple
Acer negundo Box elder
Acer nigrum Black maple
Acer platanoides Norway maple
Acer pseudoplatanus Sycamore maple
Acer rubrum var. drummondii Drummond red maple
Acer saccharinum Silver maple
Aesculus hippocastanum Horsechestnut
Ailanthus altissima Tree of heaven
Betula nigra River birch
Brahea armata Mexican blue palm
Bucida buceras Black-olive
Bursera simaruba Gumbo limbo
Calodendron capense Cape chestnut
Casuarina equisetifolia Australian pine
Catalpa speciosa Northern catalpa
Celtis occidentalis Hackberry
Conocarpus erecta Buttonwood
Cocus nucifera Coconut palm
Crataegus sp. Hawthorn
Erythrina coralloides Naked coral tree
Eucalyptus sp. Eucalyptus
Ficus sp. Fig
Fraxinus americana White ash (in areas not susceptible to Emerald Ash Borer)
Fraxinus pennsylvanica Green ash (in areas not susceptible to Emerald Ash Borer)
Fraxinus quadrangulata Blue ash
Fraxinus uhdei Shamel ash
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Ilex x attenuata Holly
Juniperus sp. Juniper
Lagerstroemia (hybrids) Crape myrtle
Larix decidua European larch
Ligustrum lucidum Glossy privet
Lysiloma sp. Wild tamarind
Maclura pomifera Osage orange
Magnolia grandiflora Southern magnolia
Malus sp. Crabapple
Morus alba White mulberry
Myrica cerifera Southern wax myrtle
Ostrya virginiana American hop hornbeam
Phellodendron amurense Amur corktree
Phoenix canariensis Canary Island date palm
Phoenix dactylifera Date palm
Pinus canariensis Canary Island pine
Pinus flexilis Limber pine
Platanus x acerifolia London plane tree
Platanus occidentalis American sycamore
Podocarpus sp. Podocarpus
Populus alba var. globosa White poplar
Populus deltoides Cottonwood
Pyrus calleryana Callery pear
Quercus agrifolia Coast live oak
Quercus bicolor Swamp white oak
Quercus imbricaria Shingle oak
Quercus lobata Valley oak
Quercus macrocarpa Bur oak
Quercus muhlenbergii Chinquapin oak
Quercus phellos Willow oak
Quercus robur Shingle oak
Quercus shumardii Shumard oak
Quercus virginiana Southern live oak
Robinia pseudoacacia Locust
Roystonea sp. Royal palm
Sabal palmetto Cabbage palm
Sapindus drummondii Western soapberry
Schinus molle California pepper tree
Styphnolobium japonica Scholar tree
Swietenia mahagoni Mahogany
Tabebuia sp. Trumpet tree
Taxodium distichum Bald cypress
Tilia americana American linden
Tilia cordata Littleleaf linden
Tilia heterophylla White basswood
Tilia platyphyllos Bigleaf linden
Tipuana tipu Tipu tree
Tristania sp. Brisbane box
Ulmus alata Winged elm
Ulmus americana American elm
Ulmus crassifolia Cedar elm
Ulmus parvifolia Lacebark elm
Ulmus pumila Siberian elm
Ulmus (hybrids) Hybrid elms
Zelkova serrata Zelkova
Listed below are this author's opinion of trees that tolerate urban environmental conditions. These trees will tolerate poor soil, poor air quality, and uneven watering. They should do well in our cities, along the streets, and on public properties. Although installing trees in sidewalk openings are not the best sites for growing trees, if there are no other options, the following trees should survive and grow reasonably well. Admittedly, trees such as the silver maple, boxelder, and tree of heaven should never be used in a city, but if you have the space and need a tree where nothing else will grow, then use them. The trees listed here will be suitable for USDA Hardiness Zones 3 – 10.
Scientific name Common name
Acacia retinodes Acacia
Acer campestre Hedge maple
Acer x freemanii Freeman maple
Acer miyabei Miyabe maple
Acer negundo Box elder
Acer nigrum Black maple
Acer platanoides Norway maple
Acer pseudoplatanus Sycamore maple
Acer rubrum var. drummondii Drummond red maple
Acer saccharinum Silver maple
Aesculus hippocastanum Horsechestnut
Ailanthus altissima Tree of heaven
Betula nigra River birch
Brahea armata Mexican blue palm
Bucida buceras Black-olive
Bursera simaruba Gumbo limbo
Calodendron capense Cape chestnut
Casuarina equisetifolia Australian pine
Catalpa speciosa Northern catalpa
Celtis occidentalis Hackberry
Conocarpus erecta Buttonwood
Cocus nucifera Coconut palm
Crataegus sp. Hawthorn
Erythrina coralloides Naked coral tree
Eucalyptus sp. Eucalyptus
Ficus sp. Fig
Fraxinus americana White ash (in areas not susceptible to Emerald Ash Borer)
Fraxinus pennsylvanica Green ash (in areas not susceptible to Emerald Ash Borer)
Fraxinus quadrangulata Blue ash
Fraxinus uhdei Shamel ash
Ginkgo biloba Ginkgo
Gleditsia triacanthos Honeylocust
Gymnocladus dioicus Kentucky coffeetree
Ilex x attenuata Holly
Juniperus sp. Juniper
Lagerstroemia (hybrids) Crape myrtle
Larix decidua European larch
Ligustrum lucidum Glossy privet
Lysiloma sp. Wild tamarind
Maclura pomifera Osage orange
Magnolia grandiflora Southern magnolia
Malus sp. Crabapple
Morus alba White mulberry
Myrica cerifera Southern wax myrtle
Ostrya virginiana American hop hornbeam
Phellodendron amurense Amur corktree
Phoenix canariensis Canary Island date palm
Phoenix dactylifera Date palm
Pinus canariensis Canary Island pine
Pinus flexilis Limber pine
Platanus x acerifolia London plane tree
Platanus occidentalis American sycamore
Podocarpus sp. Podocarpus
Populus alba var. globosa White poplar
Populus deltoides Cottonwood
Pyrus calleryana Callery pear
Quercus agrifolia Coast live oak
Quercus bicolor Swamp white oak
Quercus imbricaria Shingle oak
Quercus lobata Valley oak
Quercus macrocarpa Bur oak
Quercus muhlenbergii Chinquapin oak
Quercus phellos Willow oak
Quercus robur Shingle oak
Quercus shumardii Shumard oak
Quercus virginiana Southern live oak
Robinia pseudoacacia Locust
Roystonea sp. Royal palm
Sabal palmetto Cabbage palm
Sapindus drummondii Western soapberry
Schinus molle California pepper tree
Styphnolobium japonica Scholar tree
Swietenia mahagoni Mahogany
Tabebuia sp. Trumpet tree
Taxodium distichum Bald cypress
Tilia americana American linden
Tilia cordata Littleleaf linden
Tilia heterophylla White basswood
Tilia platyphyllos Bigleaf linden
Tipuana tipu Tipu tree
Tristania sp. Brisbane box
Ulmus alata Winged elm
Ulmus americana American elm
Ulmus crassifolia Cedar elm
Ulmus parvifolia Lacebark elm
Ulmus pumila Siberian elm
Ulmus (hybrids) Hybrid elms
Zelkova serrata Zelkova
New Trees for the City
A lot of new trees come out every year that are being bred for urban tolerance, so arborists and landscape architects should learn more about them, keep themselves up to date, and do some experimenting to check them out. It doesn’t hurt to have a plant list that contains 50% of your tried and true species and 50% new species or cultivars to try out. It may be worthwhile to conduct some trials on your own city streets even if you only plant six new trees. I can personally attest to the fact that I have found some great new trees for my city that have replaced some of my tried and true. I have been very surprised at how some unknown trees have been remarkable new additions to our tree planting list. I have also had a few failures that I will not plant again. The failures are easily replaced next year with the tried and true.
Some new trees for 2021 and 2022 include the following:
Acer saccharinum ‘JFS H1’ commonly known as Symatree™ Maple. A standout seedling, grown from seed collected from a witch’s broom, was selected by Dr. William Hoch of the University of Wisconsin for its uniquely compact growth habit, upright oval, and excellent branch structure that forms a remarkably symmetrical, upright oval tree. The leaves are light green and silvery underneath while the leaves in autumn are bright yellow to burgundy red. Neither flowers nor seeds have been observed during 20 years of observation. This Zone 3 tree grows to a height of 30 ft. and spread of 20 ft. Fact Sheet
Acer saccharum ‘Whit XLIX’ PP 23957 Powder Keg® Maple is Carl Whitmore's latest introduction. It grows 50 feet tall and 40 feet wide to form an upright oval shape of dark green leathery leaves. The leaves turn bright orange-red in autumn. This Zone 5 cultivar was selected from Caddo sugar maples of western Oklahoma. Their adaptability to heat, drought, and tough growing conditions extend far beyond its region of origin. Fact Sheet
Amelanchier alnifolia ‘Obelisk’ commonly known as Standing Ovation™ Serviceberry is a narrowly upright form of the North American native. This Zone 3 tree is a good fit for tight spaces and a good candidate for hedging. The green foliage is rounded and turns orange to red in autumn. A profuse crop of small white flowers may be followed by small, purplish blue, and edible tasty fruits. Fact Sheet
Cercidiphyllum japonicum ‘Biringer’ PP 21711 is commonly known as Hanna’s Heart® Katsura Tree. This Zone 4b tree grows to 27 ft. tall and spreads 15 ft. The smaller, upright oval and narrower stature of this mannerly Katsura is a good fit for today’s garden landscapes. Dark green, distinctively heart-shaped leaves are thick and heavily textured when young. The leaves turn yellow to orange in autumn. It has demonstrated good hardiness in Zone 4b, with fall colors lasting a bit longer than others of the species. Fact Sheet
Cercis canadensis ‘UMN7101’ is commonly known as Heart’s Desire™ Redbud. This Zone 4 tree grdos 15 feet tall and spreads 20 feet. Blooming beautifully in the Minnesota Landscape Arboretum, this exceptionally hardy introduction of the University of Minnesota welcomes spring with a profusion of lavender pink blooms. The stunning display of flowers is a welcome sight after the long, dark days of winter. In summer the medium green leaves define the rounded spreading shape and turn yellow in autumn. Fact Sheet
Corylus avellana ‘Burgundy Lace’ PP 28216 commonly known as Burgundy Lace European Filbert grows to a height of 18' and spreads to 15'. Deeply dissected burgundy leaves mature to bronze-green to orange in late summer. Slender red catkins in late wintercan produce small edible hazelnuts if a suitable pollinator is nearby. Developed and introduced by Oregon State University, this unique, Zone 4, ornamental form of European Hazel is easily maintained as a small spreading shade tree. Fact Sheet
Prunus sargentii ‘JFS KW21PS’ commonly known as Pink Myst™ Cherry does best in Zone 4. It grows in an upright oval to a height of 30' and spreads to 15'. It is also narrower and more upright in form than is typical of the species. The dark green summer leaves turn orange to orange red in autumn. Bright pink flowers, which are darker in color than other Sargent Cherry blooms, smother the branches of this unique cultivar. Fact Sheet
Styrax japonicus ‘JFS 6SJ’ commonly known as Nightfall™ Snowbell This Zone 5 tree grows to a height of just 8' and spreads to 6'. A cascade of dark purple leaves tumble from the branches of this elegant weeping tree. The dense, dark, refined foliage sets a lush, high-contrast backdrop for white buds of late spring that open to creamy white, bell-shaped flowers. Bare branches etch a graceful waterfall in the winter landscape. Fact Sheet
Ulmus chenmoui ‘JAB Morton’ commonly known as Summer Elixir™ Elm. Vase-shaped in youth, this relatively small and compact elm develops a rounded shape with age. New growth may be flushed with pink or red before maturing to green. This tree was selected by nurseryman/arborist Jim Barborinas as the best of Ulmus chenmoui seedlings shared by Dr. George Ware of Morton Arboretum. This tree has excellent insect resistance to the elm leaf beetle and tolerance to Dutch elm disease. This Zone 5 tree grows to a height of 35' amd a spread of 30'. Fact Sheet
Zelkova serrata ‘JFS KW4ZS’ commonly known as Zileration™ Zelkova. This Zone 5 tree grows to a height of 30' and spread of 25'. This tree was selected for its unusually compact structure and intermediate size. This upright, vase-shaped tree is a better fit for many landscape settings than typically larger cultivars of the species. Zileration™ has clean, dark green, fine textured summer foliage, symmetrical branching and a dense canopy make it a standout among Zelkova cultivars. The autumn color is a rusty orange. Fact Sheet
A lot of new trees come out every year that are being bred for urban tolerance, so arborists and landscape architects should learn more about them, keep themselves up to date, and do some experimenting to check them out. It doesn’t hurt to have a plant list that contains 50% of your tried and true species and 50% new species or cultivars to try out. It may be worthwhile to conduct some trials on your own city streets even if you only plant six new trees. I can personally attest to the fact that I have found some great new trees for my city that have replaced some of my tried and true. I have been very surprised at how some unknown trees have been remarkable new additions to our tree planting list. I have also had a few failures that I will not plant again. The failures are easily replaced next year with the tried and true.
Some new trees for 2021 and 2022 include the following:
Acer saccharinum ‘JFS H1’ commonly known as Symatree™ Maple. A standout seedling, grown from seed collected from a witch’s broom, was selected by Dr. William Hoch of the University of Wisconsin for its uniquely compact growth habit, upright oval, and excellent branch structure that forms a remarkably symmetrical, upright oval tree. The leaves are light green and silvery underneath while the leaves in autumn are bright yellow to burgundy red. Neither flowers nor seeds have been observed during 20 years of observation. This Zone 3 tree grows to a height of 30 ft. and spread of 20 ft. Fact Sheet
Acer saccharum ‘Whit XLIX’ PP 23957 Powder Keg® Maple is Carl Whitmore's latest introduction. It grows 50 feet tall and 40 feet wide to form an upright oval shape of dark green leathery leaves. The leaves turn bright orange-red in autumn. This Zone 5 cultivar was selected from Caddo sugar maples of western Oklahoma. Their adaptability to heat, drought, and tough growing conditions extend far beyond its region of origin. Fact Sheet
Amelanchier alnifolia ‘Obelisk’ commonly known as Standing Ovation™ Serviceberry is a narrowly upright form of the North American native. This Zone 3 tree is a good fit for tight spaces and a good candidate for hedging. The green foliage is rounded and turns orange to red in autumn. A profuse crop of small white flowers may be followed by small, purplish blue, and edible tasty fruits. Fact Sheet
Cercidiphyllum japonicum ‘Biringer’ PP 21711 is commonly known as Hanna’s Heart® Katsura Tree. This Zone 4b tree grows to 27 ft. tall and spreads 15 ft. The smaller, upright oval and narrower stature of this mannerly Katsura is a good fit for today’s garden landscapes. Dark green, distinctively heart-shaped leaves are thick and heavily textured when young. The leaves turn yellow to orange in autumn. It has demonstrated good hardiness in Zone 4b, with fall colors lasting a bit longer than others of the species. Fact Sheet
Cercis canadensis ‘UMN7101’ is commonly known as Heart’s Desire™ Redbud. This Zone 4 tree grdos 15 feet tall and spreads 20 feet. Blooming beautifully in the Minnesota Landscape Arboretum, this exceptionally hardy introduction of the University of Minnesota welcomes spring with a profusion of lavender pink blooms. The stunning display of flowers is a welcome sight after the long, dark days of winter. In summer the medium green leaves define the rounded spreading shape and turn yellow in autumn. Fact Sheet
Corylus avellana ‘Burgundy Lace’ PP 28216 commonly known as Burgundy Lace European Filbert grows to a height of 18' and spreads to 15'. Deeply dissected burgundy leaves mature to bronze-green to orange in late summer. Slender red catkins in late wintercan produce small edible hazelnuts if a suitable pollinator is nearby. Developed and introduced by Oregon State University, this unique, Zone 4, ornamental form of European Hazel is easily maintained as a small spreading shade tree. Fact Sheet
Prunus sargentii ‘JFS KW21PS’ commonly known as Pink Myst™ Cherry does best in Zone 4. It grows in an upright oval to a height of 30' and spreads to 15'. It is also narrower and more upright in form than is typical of the species. The dark green summer leaves turn orange to orange red in autumn. Bright pink flowers, which are darker in color than other Sargent Cherry blooms, smother the branches of this unique cultivar. Fact Sheet
Styrax japonicus ‘JFS 6SJ’ commonly known as Nightfall™ Snowbell This Zone 5 tree grows to a height of just 8' and spreads to 6'. A cascade of dark purple leaves tumble from the branches of this elegant weeping tree. The dense, dark, refined foliage sets a lush, high-contrast backdrop for white buds of late spring that open to creamy white, bell-shaped flowers. Bare branches etch a graceful waterfall in the winter landscape. Fact Sheet
Ulmus chenmoui ‘JAB Morton’ commonly known as Summer Elixir™ Elm. Vase-shaped in youth, this relatively small and compact elm develops a rounded shape with age. New growth may be flushed with pink or red before maturing to green. This tree was selected by nurseryman/arborist Jim Barborinas as the best of Ulmus chenmoui seedlings shared by Dr. George Ware of Morton Arboretum. This tree has excellent insect resistance to the elm leaf beetle and tolerance to Dutch elm disease. This Zone 5 tree grows to a height of 35' amd a spread of 30'. Fact Sheet
Zelkova serrata ‘JFS KW4ZS’ commonly known as Zileration™ Zelkova. This Zone 5 tree grows to a height of 30' and spread of 25'. This tree was selected for its unusually compact structure and intermediate size. This upright, vase-shaped tree is a better fit for many landscape settings than typically larger cultivars of the species. Zileration™ has clean, dark green, fine textured summer foliage, symmetrical branching and a dense canopy make it a standout among Zelkova cultivars. The autumn color is a rusty orange. Fact Sheet
Tree Care After Installation
After installing a tree, the transplant shock period is approximately one year for each inch (2.5 cm) of stem caliper. Therefore, a three-inch (8 cm) caliper tree will need at least three years in the landscape to recover from the shock. However, if the planting site is a particularly harsh site, typical for many urban planting sites, this shock period may be much longer.
Follow Up Care
After installation, be sure to indicate on maps or lists, the trees installed at their given locations. Then remove the nursery tags from the trees and shrubs to prevent girdling the branches and/or trunks. Properly mulch newly installed trees and shrubs. Apply no more than 4 inches (10 cm) of mulch to help keep the moisture in the ground. Mulch also protects the root zone from severe cold or severe heat, and it encourages mycorrhizae formation on the roots. Mulch should be kept at least 2 inches (5 cm) away from the trunk.
Install root stabilizers on trees with large crowns, those situated on windy sites, or where people might push them over. Removal of the stabilizers at the end of the first growing season is optional. If the trunk is wrapped to prevent sunscald, remove it the first spring after installation.
Ideally, all trees should be inspected annually and cared for regularly. If a tree dies, care should be taken to determine its cause before another tree is installed. If poor drainage is a problem, it should be corrected if possible. If vandalism is a problem, have neighborhood kids help install new and larger trees in these areas. The kids will develop a sense of "ownership" which will help protect the tree from future vandalism attacks. Also, add a large stake, 5 feet (1.5 m) tall, beside the tree to help protect it for its first two years in addition to the underground root stabilizers. Encourage the kids to “own” the tree by asking them to give it water once a week. Install smaller trees in parks and residential areas where vandalism is less likely to be a problem. In areas of high pedestrian traffic, it may be necessary to install pavers, stone or brick, set in sand over the tree's root ball. This will have a negative impact on the tree's growth but allow it to continue growing (albeit more slowly).
Tree Grates
Tree grates have been used for decades around the base of trees in downtown business districts. They were discussed in great detail above in the section of this Topic called Tree Installation Pits. Grates are designed to present a level surface for pedestrians and cyclists and to distribute their weight over a wide area while preventing soil compaction over the roots. They also keep the soil, mulch, or gravel that is traditionally placed around the top of the root ball from spilling out and on to the sidewalk. Tree grates also add a formal structural element to the design of the streetscape. It helps to support the growth of the trees and strengthen their resistance against harmful environmental influences. They are not for sustainable landscapes but are a short-term solution for urban landscapes. The grates should be removed from the tree as soon as it is large enough to survive in the urban landscape without it. Tree grates are less appropriate for park settings where there is usually suitable soil space for roots. Once the tree grates are removed, they should be replaced with hardy perennials serving as a living mulch. For more information on living mulch see our article in Seminar #73.
Installing low growing, hardy perennials in the tree wells should not include vines and aggressive plants. The perennials not only look attractive and discourage foot traffic over the tree roots, they also can enhance the soil quality, depending on the plants being used. Often the plants serve as a mini-rain garden.
Recent research is encouraging the use of porous materials instead of the tree grates. These materials contain small stones and pieces of wood chips or rubber shreds, held together with different types of resins. There are several products coming on the market at the present time. The resins allow water to pass through the harder particles while the rubber and wood chips provide some flexibility.
Watering
The transplant shock period should be considered as the period of intensive care. Maintenance practices should focus on preserving all the tree's leaves and eliminating or reducing all unnecessary stresses such as water stress (too much, too little), competition for root space from other plants (especially turfgrass), insect pests or pathogens that wound or defoliate the tree, nutrient deficiencies, and unnecessary wounding.
Trees provided with regular irrigation through the first growing season after transplanting require time to fully establish roots in the soil. The amount of time required is approximately 3 months (in the longer growing season of hardiness zones 9-11), 6 months (in hardiness zones 7-8), or one year or more (in the short growing season and longer winters of hardiness zones 2-6) per inch of trunk diameter. During this period, the tree’s energy should be focused on rapid root growth. Transplanted trees rely almost entirely on root ball moisture for most of the first growing season and because the root balls dry out more rapidly than the surrounding backfill, attention must focus on root ball moisture. According to recent research, for the first 4 weeks after installation, a 1-gallon (4 liter) tree requires 1 pint (½ liter) of water per day. During the next 11 weeks, 1 quart (1 liter) is used per day and for the next 21 weeks ½ gallon (2 liters) of water is used per day. However, after this point, depending on the hardiness zone, the roots should have grown into the enlarged root zone so specific root ball irrigation is no longer necessary.
Regular irrigation after installation encourages rapid root growth that is essential for tree establishment. Irrigation helps maintain and encourage the desirable dominant leader in the tree canopy on large-maturing trees. Instead of a dominant leader, trees that are under-irrigated during the establishment period often develop undesirable, low, and double leaders that can split from the tree later in its life, unless the arborist prunes the double leader.
Root Regeneration
Root regeneration occurs soon after transplanting and refers to the replacement of roots that were lost during the digging process. These new roots grow in the same direction as the original root. The rate of regeneration varies depending primarily on soil moisture, soil type, temperature, and species. Easy to transplant species such as green ash will initiate new roots as early as 17 days. Red oak is a species difficult to transplant and will take at least a month to start new roots. Trees growing in cool soils take a longer time to develop good root systems than the same trees in warm soils. In the upper Midwest where soils are frozen in winter, tree roots grow an average of 18 inches (0.5m) a year. In Florida's warm, sandy soils and a year-round growing season, tree roots will average 6 feet (2m) a year.
In balled and burlapped (B&B) transplants, it is estimated that only 4% to 8% of the original root system is contained within the root ball, depending on how the root system is measured.
Once a tree is established, many roots will have grown an eventual distance equal to approximately 3 times the height. During the establishment period, shoots and trunk grow slower than they did before transplanting. When their growth rates become more consistent from one year to the next, the tree is considered established.
When roots of bare-root trees and containerized trees are not spread out properly during installation, permanently kinked and twisted roots can result. Proper root development and anchorage will not occur, and vascular flow may be restricted. During the transplanting process, primary roots are cut so the existing branch roots often begin to grow more rapidly. This results in a more fibrous root system, typically found on nursery grown trees.
Winter Care
Snow and ice can break branches and topple entire trees. Winter sun, wind, and cold temperatures can bleach and desiccate evergreen foliage, damage bark, and injure or kill branches, flower buds, and roots.
Salt used for deicing streets is harmful to trees and landscape plantings. Salt runoff can injure roots and be absorbed by the plant, ultimately damaging the foliage. Salt spray from passing autos can also cause severe foliar or stem injury. Be sure there is plenty of spring rains to wash the salt off the foliage and flush it from the soil. If there is not, it will be necessary to provide temporary irrigation. To prevent this problem, avoid installing salt sensitive trees and shrubs in highly salted areas.
Tree Health Inspections
Various visible physical features can be observed to indicate the survival and general well-being of a newly installed tree, including the examination of the foliage, twigs, bark, and roots. The color of the foliage is an excellent diagnostic indicator. A uniform bright green color over the entire crown with leaves fully formed is a reliable indicator of good health on hardwood species. Yellowing indicates water stress from too little or too much soil moisture or may indicate various degrees of nutrient deficiencies. Yellowing and immature leaves early in the spring usually indicates stress due to soil waterlogging during the dormant season. This condition commonly occurs on trees installed in compacted soils.
Diagnosis for moisture stress of conifer foliage is somewhat more difficult. Examination of the soil conditions and roots may determine if moisture stress as a cause. Length of twig elongation as compared to previous year's growth is another indicator of plant health. Some twig shortening should be expected due to transplant shock. Installing the tree too deep can be fatal, cause rotting and eventual failure or unwanted sprouting.
Although root examination is difficult, it is recommended when serious growth symptoms appear. The color of healthy, vigorous tree root tips is white to light yellow, with smooth surfaces. Root tips affected by poor aeration are dark brown, purple or even black and have rough-looking surfaces.
These few tips will help ensure success to newly installed trees.
Note: The mention of brand names in this topic does not constitute an endorsement of these products. They are mentioned only for providing the reader with useful information.
Sources
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After installing a tree, the transplant shock period is approximately one year for each inch (2.5 cm) of stem caliper. Therefore, a three-inch (8 cm) caliper tree will need at least three years in the landscape to recover from the shock. However, if the planting site is a particularly harsh site, typical for many urban planting sites, this shock period may be much longer.
Follow Up Care
After installation, be sure to indicate on maps or lists, the trees installed at their given locations. Then remove the nursery tags from the trees and shrubs to prevent girdling the branches and/or trunks. Properly mulch newly installed trees and shrubs. Apply no more than 4 inches (10 cm) of mulch to help keep the moisture in the ground. Mulch also protects the root zone from severe cold or severe heat, and it encourages mycorrhizae formation on the roots. Mulch should be kept at least 2 inches (5 cm) away from the trunk.
Install root stabilizers on trees with large crowns, those situated on windy sites, or where people might push them over. Removal of the stabilizers at the end of the first growing season is optional. If the trunk is wrapped to prevent sunscald, remove it the first spring after installation.
Ideally, all trees should be inspected annually and cared for regularly. If a tree dies, care should be taken to determine its cause before another tree is installed. If poor drainage is a problem, it should be corrected if possible. If vandalism is a problem, have neighborhood kids help install new and larger trees in these areas. The kids will develop a sense of "ownership" which will help protect the tree from future vandalism attacks. Also, add a large stake, 5 feet (1.5 m) tall, beside the tree to help protect it for its first two years in addition to the underground root stabilizers. Encourage the kids to “own” the tree by asking them to give it water once a week. Install smaller trees in parks and residential areas where vandalism is less likely to be a problem. In areas of high pedestrian traffic, it may be necessary to install pavers, stone or brick, set in sand over the tree's root ball. This will have a negative impact on the tree's growth but allow it to continue growing (albeit more slowly).
Tree Grates
Tree grates have been used for decades around the base of trees in downtown business districts. They were discussed in great detail above in the section of this Topic called Tree Installation Pits. Grates are designed to present a level surface for pedestrians and cyclists and to distribute their weight over a wide area while preventing soil compaction over the roots. They also keep the soil, mulch, or gravel that is traditionally placed around the top of the root ball from spilling out and on to the sidewalk. Tree grates also add a formal structural element to the design of the streetscape. It helps to support the growth of the trees and strengthen their resistance against harmful environmental influences. They are not for sustainable landscapes but are a short-term solution for urban landscapes. The grates should be removed from the tree as soon as it is large enough to survive in the urban landscape without it. Tree grates are less appropriate for park settings where there is usually suitable soil space for roots. Once the tree grates are removed, they should be replaced with hardy perennials serving as a living mulch. For more information on living mulch see our article in Seminar #73.
Installing low growing, hardy perennials in the tree wells should not include vines and aggressive plants. The perennials not only look attractive and discourage foot traffic over the tree roots, they also can enhance the soil quality, depending on the plants being used. Often the plants serve as a mini-rain garden.
Recent research is encouraging the use of porous materials instead of the tree grates. These materials contain small stones and pieces of wood chips or rubber shreds, held together with different types of resins. There are several products coming on the market at the present time. The resins allow water to pass through the harder particles while the rubber and wood chips provide some flexibility.
Watering
The transplant shock period should be considered as the period of intensive care. Maintenance practices should focus on preserving all the tree's leaves and eliminating or reducing all unnecessary stresses such as water stress (too much, too little), competition for root space from other plants (especially turfgrass), insect pests or pathogens that wound or defoliate the tree, nutrient deficiencies, and unnecessary wounding.
Trees provided with regular irrigation through the first growing season after transplanting require time to fully establish roots in the soil. The amount of time required is approximately 3 months (in the longer growing season of hardiness zones 9-11), 6 months (in hardiness zones 7-8), or one year or more (in the short growing season and longer winters of hardiness zones 2-6) per inch of trunk diameter. During this period, the tree’s energy should be focused on rapid root growth. Transplanted trees rely almost entirely on root ball moisture for most of the first growing season and because the root balls dry out more rapidly than the surrounding backfill, attention must focus on root ball moisture. According to recent research, for the first 4 weeks after installation, a 1-gallon (4 liter) tree requires 1 pint (½ liter) of water per day. During the next 11 weeks, 1 quart (1 liter) is used per day and for the next 21 weeks ½ gallon (2 liters) of water is used per day. However, after this point, depending on the hardiness zone, the roots should have grown into the enlarged root zone so specific root ball irrigation is no longer necessary.
Regular irrigation after installation encourages rapid root growth that is essential for tree establishment. Irrigation helps maintain and encourage the desirable dominant leader in the tree canopy on large-maturing trees. Instead of a dominant leader, trees that are under-irrigated during the establishment period often develop undesirable, low, and double leaders that can split from the tree later in its life, unless the arborist prunes the double leader.
Root Regeneration
Root regeneration occurs soon after transplanting and refers to the replacement of roots that were lost during the digging process. These new roots grow in the same direction as the original root. The rate of regeneration varies depending primarily on soil moisture, soil type, temperature, and species. Easy to transplant species such as green ash will initiate new roots as early as 17 days. Red oak is a species difficult to transplant and will take at least a month to start new roots. Trees growing in cool soils take a longer time to develop good root systems than the same trees in warm soils. In the upper Midwest where soils are frozen in winter, tree roots grow an average of 18 inches (0.5m) a year. In Florida's warm, sandy soils and a year-round growing season, tree roots will average 6 feet (2m) a year.
In balled and burlapped (B&B) transplants, it is estimated that only 4% to 8% of the original root system is contained within the root ball, depending on how the root system is measured.
Once a tree is established, many roots will have grown an eventual distance equal to approximately 3 times the height. During the establishment period, shoots and trunk grow slower than they did before transplanting. When their growth rates become more consistent from one year to the next, the tree is considered established.
When roots of bare-root trees and containerized trees are not spread out properly during installation, permanently kinked and twisted roots can result. Proper root development and anchorage will not occur, and vascular flow may be restricted. During the transplanting process, primary roots are cut so the existing branch roots often begin to grow more rapidly. This results in a more fibrous root system, typically found on nursery grown trees.
Winter Care
Snow and ice can break branches and topple entire trees. Winter sun, wind, and cold temperatures can bleach and desiccate evergreen foliage, damage bark, and injure or kill branches, flower buds, and roots.
Salt used for deicing streets is harmful to trees and landscape plantings. Salt runoff can injure roots and be absorbed by the plant, ultimately damaging the foliage. Salt spray from passing autos can also cause severe foliar or stem injury. Be sure there is plenty of spring rains to wash the salt off the foliage and flush it from the soil. If there is not, it will be necessary to provide temporary irrigation. To prevent this problem, avoid installing salt sensitive trees and shrubs in highly salted areas.
Tree Health Inspections
Various visible physical features can be observed to indicate the survival and general well-being of a newly installed tree, including the examination of the foliage, twigs, bark, and roots. The color of the foliage is an excellent diagnostic indicator. A uniform bright green color over the entire crown with leaves fully formed is a reliable indicator of good health on hardwood species. Yellowing indicates water stress from too little or too much soil moisture or may indicate various degrees of nutrient deficiencies. Yellowing and immature leaves early in the spring usually indicates stress due to soil waterlogging during the dormant season. This condition commonly occurs on trees installed in compacted soils.
Diagnosis for moisture stress of conifer foliage is somewhat more difficult. Examination of the soil conditions and roots may determine if moisture stress as a cause. Length of twig elongation as compared to previous year's growth is another indicator of plant health. Some twig shortening should be expected due to transplant shock. Installing the tree too deep can be fatal, cause rotting and eventual failure or unwanted sprouting.
Although root examination is difficult, it is recommended when serious growth symptoms appear. The color of healthy, vigorous tree root tips is white to light yellow, with smooth surfaces. Root tips affected by poor aeration are dark brown, purple or even black and have rough-looking surfaces.
These few tips will help ensure success to newly installed trees.
Note: The mention of brand names in this topic does not constitute an endorsement of these products. They are mentioned only for providing the reader with useful information.
Sources
- Personal communications with Nancy Buley, Keith Warren, and Jeff Lafrenz of J. Frank Schmidt, Leda Marritz at Deep Root, Jim Urban at Urban Trees + Soils, and Brian Kalter at Amereq.
- Amereq Inc., "CU-SoilTM", amereq.com, 2008.
- Appleton, Bonnie, "Trees for Parking Lots and Paved Areas", Virginia Tech, Publication Number 430-028, March 2002
- Asladirt, "A New Way to Plant Urban Trees", November 18, 2010.
- Austin, Maureen E., "Tree Planting Initiatives", Journal of Arboriculture, 28(4) July 2002.
- Clatterbuck, Wayne K. "Effect of tree shelters on growth of hardwood seedlings after seven growing
seasons". USDA Forest Service General Technical Report SRS-30, Asheville, NC.1999. - Clatterbuck, Wayne K. "Post-Planting Tree Care: Fallacies and Recommendations", The University of Tennessee, 2008.
- Coder, Kim, "Training Young Trees", University of Georgia Cooperative Extension Service Forest
Resources Unit For96-35, 1996 - Conlon, Hubert P. and Wayne K. Clatterbuck. "Fertilizing Landscape Trees". The University of Tennessee, Agricultural Extension Service SP 548. Knoxville, TN. 4 p. 1999.
- Costello, Larry, "Training Young Trees", City Trees, The Journal of The Society of Municipal Arborists, Vol 37, Number 6, November/December 2001
- Deep Root products, "Silva Cells", deeproot.com/products/silva-cell, 2010.
- Dirr, Michael, “New Shade Trees in the American Landscape”, Nursery Management & Production,
January 2007 and February 2007. - Doherty, Karen, David V. Bloniarz and H. Dennis P. Ryan, "Positively the Pits! Successful Strategies for Sustainable Streetscapes", TCI Magazine - November 2003
- Gilman, Edward F, "Mycorrhizae, Irrigation Effects on Nursery Production Oaks", Journal of Arboriculture 2 7(l):30 – 39.
- Gilman, Edward F., "Planting Trees in Landscapes", Environmental Horticulture Department, IFAS, University of Florida, 2009.
- “Growing New Ideas”, and “Reference Guide”, J. Frank Schmidt & Son Co., 2011.
- Johnson, Gary, "Amending the Planting Site", Shade Tree Advocate, Vol. 1, No. 1, 2005.
- Johnson, Gary, " Establishing New Trees" University of Minnesota, Department of Forestry.
- Marzalina, E. Philip, M. and P.N. Avadhani, " Recovery Patterns Of Transplanted Trees", Arboricultural Journal 2002.
- McEvoy, C. & H. McKay , "Sensitivity of Trees in Transplanting", Arboricultural Research & Information Note 139,9 71SILN.
- Neely, Dan, and Gary Watson, "The Landscape Below Ground II", International Society of
Arboriculture, 1998. - Perry, Thomas O. "The Ecology of Tree Roots and the Practical Significance Thereof". Journal of Arboriculture 8(8):197-211.
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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, Municipal Specialist, or BCMA practice 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.
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