Growing Green: Designing gardens under trees
I have had many questions regarding planting gardens around trees. The deep shade under many trees prohibits grass from growing, leaving unsightly bare patches and exposed roots. Many of you prefer something other than this eyesore and hope to plant shade plants where grass won't grow.
However, gardening around trees presents some challenges. For one thing, the tree and the garden plants will be competing for space, nutrients and moisture. Tree roots mostly grow in the top 18 inches of soil, and spread way beyond the tree's drip line.
Shallow rooted trees, such as maple, elm, spruce, poplar and willow, are fierce competitors; deep rooted trees, like oaks and ash, are less competitive with garden plants.
Additionally, existing soil beneath the tree may be inadequate to sustain extra plant life. (That may be why nothing grows there.) However, adding soil under a tree can smother tree roots and eventually kill a tree.
Don't be discouraged! You can plant under trees. Just do so carefully and choose plants wisely. Select plants that do well in shade.
Native plants such as columbine, anemone, wild ginger, aster, violets and foam flower do well under shade trees. Non-native plants such as lily of the valley, sweet William, ground ivy, daffodil, periwinkle and vinca are also good choices.
When planting, select a root-free spot. Dig your holes with a hand trowel, plant your shady plant, and water in well. Mulch your garden with no more than four inches of shredded bark, compost, shredded leaves, cocoa shells, pine needles or wood chips. Always use permeable material under your tree to allow water to penetrate and reach the roots.
Avoid landscape plastic, as this limits the water and air that reach the roots and can suffocate your tree. Water your garden weekly to ensure good root development and healthy plants. Remember, plants need 1-1/2 inches of water weekly; trees need 10 gallons/inch trunk diameter weekly.
Black walnut trees present their own problems. Walnuts secret a substance called juglone, which kills many plants that try to grow beneath them. If you are starting a garden near a black walnut tree, try these juglone tolerant plants: daffodils, day lilies and hosta. Avoid planting juglone sensitive plants, such as peonies, columbine and nightshade plants like tomatoes, eggplant, peppers and potatoes.
If you have tried to plant a garden beneath a shade tree and have had no luck, try containers. Shady annuals like impatiens, begonias and coleus do well in containers and will add color and texture to you dark, under tree spaces.
For more information on gardening under trees, visit www.extension.umn.edu/distribution/horticulture/components/8237ppt.pdf
Until next time, happy gardening!