Help your plants thrive in a tough spot: Dry shade
When we see how quickly the soil dries out under the hot sun, it can be easy to assume that spaces in shade will stay moist. In fact, some shady areas tend to be dry, too.
“Dry shade is one of the most challenging places for plants to thrive,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle.
Dry shade often occurs beneath the branches of a large tree, because its canopy of leaves intercepts the rain like a large umbrella. Dense evergreens, such as spruces, tend to shed rain from branch to branch like a shingled roof, until the water drips off the longest branches, leaving the soil right under the tree mostly dry.
A roof overhang can create a band of dry shade near the house. A building or fence that blocks the wind may affect the rain direction in windy storms. Dry shade can even be found under plants such as large hostas, if they have broad leaves that shed rain like a roof.
“Don’t assume that just because it has rained, the rain reached all areas of your yard equally,” Yiesla said. “You really need to check the soil moisture all over the yard to figure out where your dry areas are.”
Roots that soak up water from the soil also dry it out. Some shallow-rooted trees, such as pines, spruces and silver maples, absorb much of the rain that gets past their leaves, outcompeting other plants on the ground around them. “Different plants use water differently, which can make some areas drier than others,” Yiesla said.
In the worst dry shade, such as areas beneath dense evergreens with competitive roots, no other plant can thrive. “The best thing under evergreens is a nice, even layer of mulch,” she said.
For less extreme situations, there are plants that can survive in dry shade. Many shade-tolerant ground covers and perennials, such as bishop’s hat (Epimedium), Solomon’s seal (Polygonatum), Pennsylvania sedge (Carex pensylvanica), lilyturf (Liriope) and hostas, grow well under trees and in other dry-shade areas with some watering.
Where the shade is less dense — such as under a tall tree with high branches, or in the filtered shade beneath the lacy foliage of a honey locust tree — part-shade plants may do well, such as bugleweed (Ajuga), coral bells (Heuchera), Siberian bugloss (Brunnera), and bigroot geranium (Geranium macrorrhizum). You can also plant bulbs or wildflowers that bloom in early spring before the trees’ leaves open to cast the area into shade.
Some shrubs grow well in dry shade, such as the native spicebush (Lindera benzoin) and bush honeysuckle (Diervilla lonicera). “Bear in mind that the fancy variegated leaf colors in some newer cultivars of Diervilla won’t hold up in shade,” Yiesla said.
Be careful about planting shrubs under trees. “You don’t want to dig a big hole in the root zone of an established tree,” Yiesla said. “It will damage too many of the tree’s roots.” Shrubs are a better choice under roof overhangs or in other dry shade areas away from tree roots.
Anything you plant will need regular watering for the first couple of years, and occasional watering throughout the season. Check often to make sure the soil feels at least a little moist, and water if it doesn’t.
“You always need to remember that these plants don’t have as much access to water as plants out in the open,” Yiesla said. “They may need a little more help.”