Classics
The following article has been selected because it is deemed very important to the arboricultural profession and deserves special recognition. It has appeared in a previous Seminar and because of this it is not eligible for earning certification credits; there is no test at the end of this article.
Planting under a Tree
Edited by Len Phillips
There is a right way and a wrong way to establish a garden under a tree. Being aware of a tree’s root system and the tree's cultural requirements allows the creation of a garden where new plants and the tree will live together. Caution is required to avoid damaging the tree’s roots. Also realize that the garden plants will need to cope with dry soil, shade, root competition, and ever-changing moisture and light conditions.
The Tree
Not all trees are created equal. Each requires specific light, soil, and moisture conditions to survive and remain healthy. Some tree species are extremely sensitive to major soil disturbance. Planting beneath trees that are sensitive to having their roots disturbed may need to have the proposed plantings scaled back or carried out over a few years.
Trees that will not tolerate root disturbance
Sugar maples (Acer saccharum)
Buckeyes (Aesculus spp.)
Dogwoods (Cornus spp.)
Beeches (Fagus spp.)
Larches (Larix spp.)
Magnolias (Magnolia spp.)
Pines (Pinus spp.)
Cherries and plums (Prunus spp.)
Scarlet oaks (Quercus coccinea)
Red oaks (Quercus rubra)
Black oak (Quercus velutina)
Lindens (Tilia spp.)
Hemlocks (Tsuga spp.)
Trees that tolerate some root disturbance
Red maples (Acer rubrum)
River birches (Betula nigra)
Hornbeam (Carpinus spp.)
Hickories (Carya spp.)
Redbuds (Cercis canadensis)
White ashes (Fraxinus americana)
Ironwood (Ostrya virginiana)
Sourwood (Oxydendrum arboreum)
Spruces (Picea spp.)
Sycamore (Platanus occidentalis)
Swamp white oak (Quercus bicolor)
Trees that tolerate root disturbance
Silver maples (Acer saccharinum)
Pecan (Carya illinoinensis)
Hawthorns (Crataegus spp.)
Ginkgos (Ginkgo biloba)
Honeylocusts (Gleditsia triacanthos)
Kentucky coffeetree (Gymnocladus dioicus)
Crabapples (Malus spp.)
Poplars (Populus spp.)
White oak (Quercus alba)
Willows (Salix spp.) Arborvitae (Thuja spp.)
The Tree Roots
Massive undertakings to alter the grade of the landscape or to change soil pH under a tree are difficult and often impractical. Adding a layer of soil that is more than 2 inches deep, for example, can reduce moisture and oxygen availabilities, and hinder gas exchange to existing roots, causing sensitive trees to suffer and even die. Most trees have large major roots that extend several feet into the soil to anchor them against strong winds. The majority of a tree’s roots, however, are small woody roots with fine-hair roots that grow within the upper 12 to 18 inches (30-45 cm) of soil and extend far beyond the tree’s drip line. These roots are responsible for absorbing water and nutrients from the soil. A tree’s root system and canopy determine how easy or difficult it will be to install a garden under a tree. It can be particularly troublesome to work among the extensive surface roots of shallow-rooted trees such as maples (Acer spp.) and elms (Ulmus spp.). The dense canopies and umbrella-like habits of trees such as conifers, Norway maples (Acer platanoides), and lindens (Tilia spp.) not only block sunlight but also deflect rainfall. Only the toughest garden plants have a chance of surviving in such conditions. Before starting a garden, if turfgrass is growing or attempting to grow under the tree, the grass needs to be removed.
Avoid stripping the grass with hand tools or equipment, which not only is backbreaking work but also damages a tree’s fine roots. Try instead to smother the grass with five or six layers of wet newspaper, topped with a layer of organic mulch 1 to 2 inches (2-5 cm) deep. The downside of this method is that it may take two to three months to kill the grass. Chemicals such as glyphosate (Roundup) will kill the grass faster but it’s important to avoid spraying herbicides on the tree because they can be absorbed through the bark. Heavy doses of broadleaf herbicides near tree roots could also harm the tree because it is a broadleaf plant.
The Garden Planting
When purchasing plants to grow under trees, think small! Find the right plant and buy it in the smallest size available. Smaller plants require a petite planting hole that will minimize the disturbance to tree roots. More plants may have to be purchased, but it will be easier tucking them among the tree’s roots.
It’s best for the tree to disturb the soil only where new plants are being installed. Do not cultivate the entire proposed garden area. If a root larger than 1½ to 2 inches (4-5 cm) in diameter is encountered while digging a hole for a garden plant, move the planting hole a few inches away to avoid slicing through the root. It will be okay if small tree roots are cut when digging because they will regenerate fairly quickly. When planting, spread out the roots of the garden plants as much as possible to ensure good contact with the surrounding soil. To avoid wounding the tree bark, which is an open invitation to insect and disease problems, start planting at least 12 inches (30 cm) away from the trunk and work outward.
When all the garden plants have been installed, water the entire area to settle them and the soil. Then spread a 2 to 3 inch (5-8 cm) deep layer of composted organic mulch, such as wood chips or bark mulch, throughout the garden area to conserve moisture and keep the weeds down. The moisture that mulch can hold against a tree’s bark is conducive to rot and disease, so be sure to keep the mulch at least 2 inches (5 cm) away from the base of the tree.
Because the little garden plants with their tiny root systems are competing with a large, established tree, thoroughly water the area after planting and continue to do so, especially during dry spells, until these plants are established. Expect some losses because the small plants will not be able to compete with the tree's roots.
Avoid fertilizing for the first year after planting because it encourages more top growth than root growth. The roots are where new plants need to spend their energy if they are going to survive. If a nutrient deficiency is suspected, get a soil test first to confirm the problem. If needed, a general, slow release, balanced fertilizer, which benefits large trees as well as the garden plantings, can be broadcast throughout the garden and watered in well. Annually apply a light topdressing of composted organic matter (such as wood chips, bark mulch, compost, shredded leaves, or well-rotted manure) to the mulched area in spring to maintain a 2 to 3 inch (5-8 cm) deep layer of mulch. This topdressing naturally enriches the soil by adding nutrients and enhancing aeration and moisture-holding capacity. As it decomposes, it loosens heavy clay, improves drainage, and allows the plant roots to become established. Organic matter also encourages the activity of beneficial organisms that mix and aerate the soil. By following this procedure, the tree becomes more amenable to sharing its territory, and a shade garden will begin to appear.
Plants for dry shade
When planting a garden under mature trees, the chances of success are improved by choosing plants that are suited to the site conditions. Keep in mind that the reduced sun and moisture levels may reduce the growth rate and flowering potential of the plants.
Here is a list of plants that can grow in the reduced light and moisture available under many trees.
Shrubs
Carolina allspice (Calycanthus floridus)
Cutleaf stephanandra (Stephanandra incisa)
Ninebark (Physocarpus opulifolius)
Snowberry (Symphoricarpos albus var. laevigatus)
Winterberry (Ilex verticillata)
Perennials and grasses
Black snakeroot (Cimicifuga racemosa)
Columbine (Aquilegia spp.)
Foamflower (Tiarella spp.)
Japanese forest grass (Hakonechloa macra)
Japanese painted fern (Athyrium niponicum var. pictum)
Lungwort (Pulmonaria spp.)
Siberian iris (Iris spp.)
Source
The following article has been selected because it is deemed very important to the arboricultural profession and deserves special recognition. It has appeared in a previous Seminar and because of this it is not eligible for earning certification credits; there is no test at the end of this article.
Planting under a Tree
Edited by Len Phillips
There is a right way and a wrong way to establish a garden under a tree. Being aware of a tree’s root system and the tree's cultural requirements allows the creation of a garden where new plants and the tree will live together. Caution is required to avoid damaging the tree’s roots. Also realize that the garden plants will need to cope with dry soil, shade, root competition, and ever-changing moisture and light conditions.
The Tree
Not all trees are created equal. Each requires specific light, soil, and moisture conditions to survive and remain healthy. Some tree species are extremely sensitive to major soil disturbance. Planting beneath trees that are sensitive to having their roots disturbed may need to have the proposed plantings scaled back or carried out over a few years.
Trees that will not tolerate root disturbance
Sugar maples (Acer saccharum)
Buckeyes (Aesculus spp.)
Dogwoods (Cornus spp.)
Beeches (Fagus spp.)
Larches (Larix spp.)
Magnolias (Magnolia spp.)
Pines (Pinus spp.)
Cherries and plums (Prunus spp.)
Scarlet oaks (Quercus coccinea)
Red oaks (Quercus rubra)
Black oak (Quercus velutina)
Lindens (Tilia spp.)
Hemlocks (Tsuga spp.)
Trees that tolerate some root disturbance
Red maples (Acer rubrum)
River birches (Betula nigra)
Hornbeam (Carpinus spp.)
Hickories (Carya spp.)
Redbuds (Cercis canadensis)
White ashes (Fraxinus americana)
Ironwood (Ostrya virginiana)
Sourwood (Oxydendrum arboreum)
Spruces (Picea spp.)
Sycamore (Platanus occidentalis)
Swamp white oak (Quercus bicolor)
Trees that tolerate root disturbance
Silver maples (Acer saccharinum)
Pecan (Carya illinoinensis)
Hawthorns (Crataegus spp.)
Ginkgos (Ginkgo biloba)
Honeylocusts (Gleditsia triacanthos)
Kentucky coffeetree (Gymnocladus dioicus)
Crabapples (Malus spp.)
Poplars (Populus spp.)
White oak (Quercus alba)
Willows (Salix spp.) Arborvitae (Thuja spp.)
The Tree Roots
Massive undertakings to alter the grade of the landscape or to change soil pH under a tree are difficult and often impractical. Adding a layer of soil that is more than 2 inches deep, for example, can reduce moisture and oxygen availabilities, and hinder gas exchange to existing roots, causing sensitive trees to suffer and even die. Most trees have large major roots that extend several feet into the soil to anchor them against strong winds. The majority of a tree’s roots, however, are small woody roots with fine-hair roots that grow within the upper 12 to 18 inches (30-45 cm) of soil and extend far beyond the tree’s drip line. These roots are responsible for absorbing water and nutrients from the soil. A tree’s root system and canopy determine how easy or difficult it will be to install a garden under a tree. It can be particularly troublesome to work among the extensive surface roots of shallow-rooted trees such as maples (Acer spp.) and elms (Ulmus spp.). The dense canopies and umbrella-like habits of trees such as conifers, Norway maples (Acer platanoides), and lindens (Tilia spp.) not only block sunlight but also deflect rainfall. Only the toughest garden plants have a chance of surviving in such conditions. Before starting a garden, if turfgrass is growing or attempting to grow under the tree, the grass needs to be removed.
Avoid stripping the grass with hand tools or equipment, which not only is backbreaking work but also damages a tree’s fine roots. Try instead to smother the grass with five or six layers of wet newspaper, topped with a layer of organic mulch 1 to 2 inches (2-5 cm) deep. The downside of this method is that it may take two to three months to kill the grass. Chemicals such as glyphosate (Roundup) will kill the grass faster but it’s important to avoid spraying herbicides on the tree because they can be absorbed through the bark. Heavy doses of broadleaf herbicides near tree roots could also harm the tree because it is a broadleaf plant.
The Garden Planting
When purchasing plants to grow under trees, think small! Find the right plant and buy it in the smallest size available. Smaller plants require a petite planting hole that will minimize the disturbance to tree roots. More plants may have to be purchased, but it will be easier tucking them among the tree’s roots.
It’s best for the tree to disturb the soil only where new plants are being installed. Do not cultivate the entire proposed garden area. If a root larger than 1½ to 2 inches (4-5 cm) in diameter is encountered while digging a hole for a garden plant, move the planting hole a few inches away to avoid slicing through the root. It will be okay if small tree roots are cut when digging because they will regenerate fairly quickly. When planting, spread out the roots of the garden plants as much as possible to ensure good contact with the surrounding soil. To avoid wounding the tree bark, which is an open invitation to insect and disease problems, start planting at least 12 inches (30 cm) away from the trunk and work outward.
When all the garden plants have been installed, water the entire area to settle them and the soil. Then spread a 2 to 3 inch (5-8 cm) deep layer of composted organic mulch, such as wood chips or bark mulch, throughout the garden area to conserve moisture and keep the weeds down. The moisture that mulch can hold against a tree’s bark is conducive to rot and disease, so be sure to keep the mulch at least 2 inches (5 cm) away from the base of the tree.
Because the little garden plants with their tiny root systems are competing with a large, established tree, thoroughly water the area after planting and continue to do so, especially during dry spells, until these plants are established. Expect some losses because the small plants will not be able to compete with the tree's roots.
Avoid fertilizing for the first year after planting because it encourages more top growth than root growth. The roots are where new plants need to spend their energy if they are going to survive. If a nutrient deficiency is suspected, get a soil test first to confirm the problem. If needed, a general, slow release, balanced fertilizer, which benefits large trees as well as the garden plantings, can be broadcast throughout the garden and watered in well. Annually apply a light topdressing of composted organic matter (such as wood chips, bark mulch, compost, shredded leaves, or well-rotted manure) to the mulched area in spring to maintain a 2 to 3 inch (5-8 cm) deep layer of mulch. This topdressing naturally enriches the soil by adding nutrients and enhancing aeration and moisture-holding capacity. As it decomposes, it loosens heavy clay, improves drainage, and allows the plant roots to become established. Organic matter also encourages the activity of beneficial organisms that mix and aerate the soil. By following this procedure, the tree becomes more amenable to sharing its territory, and a shade garden will begin to appear.
Plants for dry shade
When planting a garden under mature trees, the chances of success are improved by choosing plants that are suited to the site conditions. Keep in mind that the reduced sun and moisture levels may reduce the growth rate and flowering potential of the plants.
Here is a list of plants that can grow in the reduced light and moisture available under many trees.
Shrubs
Carolina allspice (Calycanthus floridus)
Cutleaf stephanandra (Stephanandra incisa)
Ninebark (Physocarpus opulifolius)
Snowberry (Symphoricarpos albus var. laevigatus)
Winterberry (Ilex verticillata)
Perennials and grasses
Black snakeroot (Cimicifuga racemosa)
Columbine (Aquilegia spp.)
Foamflower (Tiarella spp.)
Japanese forest grass (Hakonechloa macra)
Japanese painted fern (Athyrium niponicum var. pictum)
Lungwort (Pulmonaria spp.)
Siberian iris (Iris spp.)
Source
- Taylor,
Doris, “ Planting under a Tree”, Fine Gardening, Vol.105, pp.
40-43