Most people that have yards that are shaded by trees will have areas of “dry shade.” In our climate in the Washington, DC metropolitan area, we have extended dry periods, or even drought conditions, nearly every summer. I have a shady yard, with clay soil and cover from tall oaks, tulip poplars, and the charmingly-named pignut hickory. The lot slopes enough that the lower end of the yard floods in heavier rains. Even this area gets quite dry in late summer. I usually wind up watering once every week or two in dry spells—even with drought-tolerant plants, this will result in more attractive [and stronger/less-stressed] plants. So, my recommendations are based on some drought-stress with a bit of mercy thrown in. Also bear in mind that when plants are newly planted, they need to be watered periodically until they are established. Further bear in mind that there are degrees of shade, and virtually all “shade” plants do better if they get at least a couple of hours of morning sun. Your type of tree cover makes a difference as well. If you have shallow-rooted aggressive trees like Norway maples or evergreen trees, it will be difficult growing anything under them. So, with the usual disclaimer that results may vary, here is what I have found over the years.
Consider bulbs. Many of the fall-planted hardy bulbs/corms we plant come from climates with long, dry summers. Under deciduous trees, they get sunlight until the trees leaf out in late April, then they go dormant till next spring. The ones that have done the best for me over the years are Spanish bluebells (Hyacinthoides hispanica), grape hyacinth (Muscari botryoides), snowdrops (Galanthus), and hardy cyclamen.
For perennials, barrenwort (Epimedium) works well as a ground cover at the base of trees. Some are evergreen to the extent in that they stay green in mild winters. Usually you wind up cutting off the old, ratty foliage before the new growth and flowers appear in April or May. For me, the yellow-flowered cultivars that I planted many years ago–‘Sulphureum’ (better flowers) and ‘Frohnleiten’ (better foliage)—have been the most vigorous. We never have a lot of Epimedium in stock, so ask the staff for their recommendations if these are not available.
Woodland aster, Eurybia (Aster) divaricata, is a native forest-edge plant with white flowers and a rambling growth habit. It will seed around for you and provide some color in late summer.
If you want a grassy-look, try a sedge—Carex—some of which, like Carex appalachica, will take dry shade. I put some of these cute little mounded “grasses” in about ten years ago. They haven’t spread, but they come back reliably.
Two ferns to try: our native Christmas fern, and the Asian Autumn fern. Christmas fern grows on hillsides in our local forests, and can go weeks without water. In my garden, I have autumn fern in a very shaded spot next to the house, and it never gets supplemental watering. Both are evergreen (although they lie down in the winter) and the autumn fern has attractive bronze-colored new growth.
Our go-to plant for deer resistance, Hellebore, also takes dry soil, but if it gets too dry or is exposed to afternoon sun, it will wilt and look pretty unhappy. Springs back with watering.
On the edge: best with a half day or more of sun, but quite drought tolerant, are daylilies and mountain mint. Daylilies come in all colors but true blue, and can go for weeks without water. (Stay away from the invasive orange “ditch daylily.”) When Behnke’s used to have a garden center in Potomac, MD, we had a patch of mountain mint (Pycnanthemum muticum) under a tree in poor soil at the edge of the driveway, where it got mid-afternoon sun; No supplemental watering. The deer left it alone, and pollinators love it. It looks better in full sun and good, moist soil, in which conditions it spreads very quickly and can be hard to control, but it is adaptable to dry soil. In my experience full shade will not work.
Hostas hold on pretty well in dry weather, especially established clumps with large, thick leaves. As the days pass without water, the older leaves will shrivel, but the plant itself will survive for weeks without water.
Euphorbia amydaloides subspecies robbiae does best with a half day or more of sun—the more sun, the fuller the planting—but in my yard it gets by with just a couple of hours. With more light it makes a full, evergreen ground cover, in less light, it’s an open-growing, spreading accent plant that I intermix with hellebores.
In the traditional evergreen perennial ground covers, liriope and Japanese pachysandra both tolerate dry soil.
by Larry Hurley, Behnke horticulturist