In Winnipeg, we're fortunate to have so many older neighbourhoods with large trees. Those towering elms, pines, and spruces are certainly beautiful, and when summer heats up, they provide cooling shade to homes and yards. But it's not always easy to grow ornamental plants underneath them.
Mature trees don't just block sunlight, they also have massive root systems that are greedy for moisture. The result is dry shade, one of the most common problem areas in a garden. Similar conditions can also prevail under your eaves, an area that often gets minimal sun and no rain. With so little light and moisture, most plants, including many shade-lovers, will languish and die. What to do?
Well, don't just give up and plant bishop's goutweed (Aegopodium podagraria). Though often touted as a 'grow-anywhere' perennial, it's a thug. It spreads by myriad underground runners and is harder to get rid of than quackgrass. The future stewards of your garden will curse you. There are much better alternatives.
In her Wolseley yard, my friend, Ann, grows a nice selection of perennials under a large spruce tree. Some people believe plants won't grow under evergreens because the soil is too acidic, but that's usually not the problem. Even years of fallen needles can't change the typically alkaline pH of our local soil that much. The problem is dryness caused by competition from the tree roots.
Recognizing this, Ann followed the recommendations for dry shade in Lois Hole's book, Perennial Favorites, planting among others Solomon's seal, lady's mantle (Alchemilla mollis) and bergenia.
She's been happy with the results. Bergenia's pink blooms are among the very first in spring. Solomon's seal blooms a bit later, with its graceful rows of little white bells on arching branches. The foliage of both plants remains handsome all season. In June and July, the fluffy chartreuse flowers of lady's mantle appear, a perfect filler for bouquets. The leaves look spectacular after a rain, beaded with sparkling droplets.
Ann reports she only has to water the bed once or twice each summer if there's normal rainfall, or about every two weeks if it's dry.
In a front yard shaded by boulevard elms, I've had good luck with three other perennials: fleeceflower (Persicaria affinis a.k.a. Polygonum affine), bigroot cranesbill (Geranium macrorhizum), and barrenwort or bishop's hat (Epimedium rubrum).
The barrenwort spreads slowly in our climate, but it has lovely star-shaped flowers in the spring and beautiful, refined foliage.
The fleeceflower and cranesbill are excellent ground covers, each producing attractive pink flowers and handsome, weed-smothering foliage, even in dry conditions. Fleeceflower blooms over a long period, from summer into fall.
Before you invest in these or any other plants, take time to improve the soil where you want them to grow. No matter how drought-tolerant, they will not thrive in compacted clay.
Incorporate lots of compost or other organic matter into the soil so as to retain as much moisture as possible. Mature trees tend to fill flower beds throughout your yard with their small feeder roots, so you may have to break those up with your spade.
If you're working on top of larger tree roots, don't till or dig up the whole area, but create planting pockets here and there among the roots. Under no circumstances should you pile topsoil under a tree, thinking you will make a raised bed. It will smother the tree's roots, which can cause serious damage, though you may not see it right away. It's OK to put down two inches of a light mulch, like shredded bark, to retain moisture, but keep it well away from the trunk.
Remember all plants need at least some water in order to grow, especially while they're establishing themselves. You'll have to provide supplemental irrigation while the plants are young or during long dry spells. Flower beds under the rain shadow of eaves will always need occasional watering, no matter what you plant in them.
Familiar bedding plants for shade like impatiens and begonias are not happy in dry soil and will need extra watering to do well. However, I've found a couple of tropical houseplants that seem tolerant of dry shade: purple heart, spider plant, and flowering maple (Abutilon). You can bring them inside again in the fall, or treat them like annuals and leave them to the frost.
Under deciduous trees, try spring-blooming bulbs. Before the trees leaf out, daffodils and tulips can usually soak up enough sun to develop their cheery blooms, and their bulbs provide some drought protection. If you love lilies, plant the martagons, which send up their dancing turk's caps even in shade. The early, scented lemon daylily (Hemerocallis flava) has also performed quite well in my front yard.
If you want a taller plant for dry shade, consider goatsbeard (Aruncus dioicus). Reaching about four feet tall and wide, it boasts feathery plumes of creamy white flowers in early summer. Very striking.
Or maybe you're looking for a shade- and drought-tolerant shrub. Choices are limited, but your best bet is probably our native highbush cranberry (Viburnum trilobum). Compact varieties mature at about six feet tall and wide, with attractive white flowers in spring and reddish fall foliage.
Linda Dietrick teaches at the University of Winnipeg. She has been gardening in Winnipeg for over 20 years and enjoys sharing her research and experience with other gardeners.
A shady situation
CONVINCED that nothing will grow beneath the shady canopy of a mature tree on your property?
Ordering a load of river rock is not the only solution for covering the dry, bare ground. Colourful, but temporary, gardeners will sometimes try planting impatiens under a shady tree. Impatiens, though, requires plenty of water. A more long-term solution is to plant hardy, shade-loving perennials that are tolerant of dry shade.
Today's contributor, gardening enthusiast Linda Dietrick, recommends interesting options that do not include the ubiquitous hosta. Linda is one of the many workshop presenters at this year's Gardening Saturday on March 31. Visit www.gardensmanitoba.com for full details.
Mark your calendars for a fascinating new nature documentary, Smarty Plants, premièring on CBC-TV's The Nature of Things on Thursday, March 22 at 8 p.m. A collaboration between local production company Merit Motion Pictures and The Nature of Things, this one-hour documentary looks at plant intelligence and behaviour.
Gardeners will recall the popular Recreating Eden, a five-year-long series by Merit Motion Pictures. Merit Motion Pictures took their cameras into the Winnipeg garden of John Tinkler as well as the vegetable garden at Fort Whyte. Ernie Buffie, film director with Merit Motion Pictures says, "People who are working with plants know intuitively that plants have an enormous capacity to respond to the environment."
-- Colleen Zacharias
