Very helpful column. Do you have any suggestions for bushes 4-6 feet
tall that would grow in the dry shade under trees in zone 4?
In My Garden Blog
Western Mountains and High Plains
June 18, 2009
By
John Cretti,
Denver, CO
One of my favorite new ground covers for dry shade is Erysimum 'Jenny Brook'.
Living Ground Covers Beneath Large Shade Trees
As our landscapes begin to mature and shade trees and evergreens enlarge their canopy, many of us want to continue to grow a lush green lawn beneath the shade of the trees. This can be an daunting task as the areas beneath trees are not conducive to growing a lawn. Just take a lesson from nature and observe wild areas where grasses are thin or nonexistent under trees. Instead, naturalized ground covers have filled in the spots or a natural accumulation of mulch exists to cover the ground.
Take the area beneath my maturing elm tree, or any other large, deciduous shade tree. The soil tends to dry out faster and the intensity and duration of light has been decreased. This inhospitable environment is filled with greedy tree roots that rob water and nutrients from competing plants, including any lawn grasses. An area that once supported a lush green lawn is now thinning and becoming invaded by opportunistic weeds that are quick to fill in the voids.
Wild morning glory or bindweed, Canada thistle, clovers, wild violets, and other weed species are likely to become the norm. So what is the alternative? It doesn't necessarily mean you have to lay down a landscape fabric and cover the area with gravel or bark mulch.
There are a good selection of ground cover plants that will grow within the shade zone of large trees to which I give the term "dry shade". But before you decide to go this direction, it is important to get the soil in the area conditioned with some compost and get rid of those invading weeds.
You will need to prepare the area by removing the existing vegetation and yet be careful not to harm the roots of the shade tree. My preference is to dig and hand pull out the weeds after a good soaking of the area. Take care when digging so you won't cut or tear into the roots of the tree. Weed killers are discouraged as the residue they leave can ultimately harm the tree and make planting of new plants less successful.
Once the weeds are eliminated, scatter compost over the area -- a couple of inches will suffice -- and gently and carefully work it into the planting area. You only need to work the compost down a few inches or so and then lightly water it in. No rototilling allowed! Work slowly, gently, careful not to cut or severely damage the roots of the trees. Remember, some trees have shallow root systems and root damage can adversely stress your tree.
Now do your homework and decide which ground covers are to your liking. Think about interesting foliage, texture, flowers, height, and spread.
Some ground covers to consider: Pussytoes (Antennaria parviflora) is attractive with evergreen, silver-gray leaves; spotted dead nettle, (Lamium spp), with silver-banded foliage, striped foliage, or green foliage and bearing pink or white flowers; Sedum kamtschaticum 'Variegatum', with colorful foliage and orange-yellow flowers; sweet woodruff (Galium odoratum, a semi-evergreen plant with white flowers in spring; creeping cranesbill (Geranium macrorrhizum, with rose or white flowers in spring; periwinkle Vinca minor, with blue or white blooms and evergreen foliage; variegated euonymus; alpine strawberry Fragaria vesca, with semi-evergreen foliage and attractive white spring flowers and edible berries. One of my new favorites is Erysimum 'Jenny Brook'. The foliage remains mostly evergreen throughout the seasons.
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K. Earl
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John C.
You can learn more about the various ground covers in my books:
Rocky Mountain Gardener's Guide and Month-by-Month Gardening in the
Rocky Mountains (Cool Springs Press). There is an entire chapter
dedicated to ground covers and their attributes and uses.