Ground Covers: Made In the Shade

Welcome to midsummer! Not really a dream, is it? The hot, blistering sun is back and many of us are trying to spend a lot of our outdoor time in the cool, dappled shade of large spreading trees. As your sunflowers and tomatoes shoot up to the heavens, why not look under your leafy canopies and start giving some thought to shade gardening?

Perhaps one of the most common -- and frustrating -- stumbling blocks in home landscaping is getting grass to grow under trees. Die-hard lawn jockeys spend many weekend hours at garden centers looking for "shade-loving" grass seed. Others go on a liming rampage, dumping bag loads on their lawn to wipe out the lush green, gentle mosses which love acid soils and shady, humid conditions. Worse, yet, others will rip up their lawns in fall, damaging tree roots, and chewing up precious weekend hours, determined to get a good stand of grass growing at any cost.

What's going on? Grass is not a shade-loving plant. Ever see thick, velvety carpets of grass in a forest or woodland? Moss, yes, and ferns, blueberries, and Partridgeberry. No grass.

Grass is a plant of wide open prairies and sun-drenched meadows. Taking a plant that evolved and adapted to these conditions and trying to get it to grow in full shade is almost impossible, and only marginally successful in part-shade. Several varieties of Kentucky Bluegrass are shade tolerant, but only to a degree. The real answer lies in rethinking your landscape.

More and more often, savvy gardeners and landscapers are replacing unsuccessful grassy areas with mulches or ground covers -- or, preferably, a creative combination of the two. Best of all, these lawn alternatives offer a host of aesthetic, horticultural, and environmental benefits.

Save the trees!

Apart from man-made structures, trees create most of the shade in and around our yards, in addition to providing much of the beauty and a cool retreat from summer heat. But tree roots and grass do not get along well. Grass is one thirsty plant, and its root system can and does compete with the root system of trees -- the majority of which are quite shallow. During long, dry periods, grass can suck up the moisture critical to tree health and survival, which can lead to severe stress and even mortality. This situation is exacerbated when a tree is already suffering other stress conditions such as defoliation by Gypsy moths caterpillars, other pest attacks, and the environmental stresses of air pollution, compacted soil, bark injuries, and so on. As long as a tree has ready access to the moisture it needs, it can generally withstand most seasonal assaults. But having grass quickly taking up its water can lead to decline and death.

Mulching under the dripline of a tree -- the area under the leafy canopy -- will both provide organic nutrients and ensure a ready supply of moisture. Using some of the ground covers suggested below in conjunction with mulch or by themselves will also work while providing natural beauty through the plant's foliage, flowers, or fruits. And ground covers coexist nicely with trees as they do not compete aggressively for moisture.

Another benefit of mulches and ground covers is trunk protection. A great many of the diseases which afflict trees in both yards and parklands enter a tree's vascular system through cuts and gouges in bark and exposed roots. Running lawn mowers over roots and into trunks is a major source of tree injury, as are weed-whackers, especially around smaller diameter trees (like the dogwood on your front lawn). Keep machinery away from trees by keeping the grass away too.

A Woodland Garden

There are scores of readily available ground covers ideally suited for use in the shade. Regrettably, the most commonly utilized plants are non-native, overused to the point of being boring, and frequently -- almost frighteningly -- invasive. Using native species has the merit of recreating a peaceful woodland habitat, even if only under a single tree! And many of these native ground covers contribute to restoring our local habitat: providing food and cover for a variety of wildlife.

The Big Four

Yawn. No other ground covers are used more often than Periwinkle (Vinca minor), Pachysandra (Pachysandra terminalis), Bugleweed (Ajuga reptens), and Common or English Ivy (Hedera helix). Running a close fifth is Liriope (various species). In their defense, they do everything a ground cover should do -- and should not be overlooked. They are perhaps the least expensive and quickest spreading. Also the most hardy. And aggressive. Ivy will shimmy up trees, up walls, inside rain spouts. And Ajuga has been known to romp across a lawn while owners aren't looking. Bear in mind while shopping for plants that these favorites are often available in a variety of colors and textures: for example, Ajuga cultivars can have bronze, burgundy, or even variegated foliage. Ivy can be found in over 130 forms, although the common English Ivy is best avoided. Best of all, many of these plants are easily propagated by simple division and transplanted to new sites where they will also fill in quickly.

Return of the Natives

There are now more wonderful options native options available to the home gardener than ever before. Wild Ginger (Asarum canadense) is a personal favorite with fragrant stems and roots, discrete purple-maroon flowers, which will appreciably cover an area in about two years (plant 12" apart). Some gardeners claim that it's delicious when candied.

As a home-grown alternative to the ubiquitous Pachysandra, a.k.a. Japanese Spurge, consider substituting Allegheny Spurge (Pachysandra procumbens): this hardy native features an attractive grey-green mottled foliage reminiscent of river trout.

If moss has taken hold under your trees, consider interplanting Partridgeberry (Mitchella repens), a slow-growing plant with small, glossy green leaves, white veins, fragrant pinkish flowers, and shiny red berries. Moss, incidentally, can help create a miniature Japanese garden under a tree by adding some interesting stones and rocks. You can help moss spread by taking a small donor patch, mixing thoroughly with buttermilk, and spraying over a suitable humus-rich area. Feed moss with a manure or compost tea.

Many nurseries now offer a wide range of ferns such as Maidenhair (Adiantum pedatum), Fancy (Dryopteris austriaca), and familiar Christmas Fern (Polystichum acrostichoides), all of which can help add a soft yet wild side to your shade garden. For best effect, intermingle a number of different fern genera and species with other lower-growing ground covers -- even the Big Four!

Other native plants to combine with ground-huggers include the Crested Iris (Iris cristata) with showy yellow crests and lavender throats, red and yellow-flowered Eastern Columbine (Aquilegia canadensis), and numerous species in the Phlox genus, especially the rich-scented Wild Sweet William (Phlox divartica), or other varieties of Creeping Phlox, which offer every pastel shade imaginable.

For more ground coverage, consider some of the native sedums, Barren Strawberry (Waldsteinia fragarioides), or Creeping Dogwood (Cornus canadensis). In instances like the Creeping Dogwood or "Bunchberry," as is the case with most natives, be sure to obtain your plants from a reputable source: some species are protected and rare; do not allow your expansion of a backyard habitat to infringe on natural areas elsewhere.

You need not stick with natives alone, of course. Non-invasive ground covers can also add beauty and flavor to your garden. For instance, Sweet Woodruff (Galium odoratum) is a fast spreading plant with bright white flowers in spring, and fragrant leaves and stems which are used as the flavoring May Wine (use the inexpensive white wine of your choice) and fruit compotes. Bishop's Weed (Aegopodium podograria) is gaining in popularity, especially the variegated variety ('Variegatum'), which isn't as weedy as the name suggests and sports a beautiful light green and white foliage and clusters of white flower.

On a larger scale, many gardeners are turning to the scores of Hostas on the market: while some remain small and compact, others can quickly fill or dominate a shady area with colors from gold to blue, a range of textures, and sometimes towering, fragrant flower scapes.

The final word on ground covers is diversity. You can always select from among the Big Four and use them alone -- or help preserve some of our region's shrinking biological diversity and substitute native perennials. You can even mix ground covers and taller shade lovers to create a dripline wildlife preserve. Grow a moss garden -- or mulch first and start planting. Start slowly, as your budget permits, and space plants properly for coverage in one to two years. Remember that your high-maintenance, low performance lawn is probably trying to tell you something. Do something different!

Copyright 2009, Joseph M. Keyser