Ground-Covers for Hillside Gardens

Plants that ramble and scramble over the ground are great problem solvers for inclines that are too steep to mow but not too steep to plant. At their best, ground-covers form a thick carpet of foliage that excludes weeds, retains moisture, and protects the soil against erosion.

Simplicity is the design key to getting stellar results from ground-covers grown on sloping ground. The beauty of a carpet of bugleweed or moss phlox comes from the solid mass of flowers it produces when it is in bloom. After the flowers have passed, the consistency of the foliage texture and color kicks in to extend the show. Slopes planted with broad bands of only a few species of plants are also much easier to maintain than a mixed collection of different plants. Trimming, feeding, and weeding can be done quickly and efficiently.

The Textures of Ground-Covers

Plant texture provides clues that you can use when deciding what plant to put where. Visually, the fine texture of plants with small leaves causes them to appear to be farther away than they actually are. The coarse texture of plants with thick stems and larger leaves, appear closer to a viewer than they actually are. So, if you place plants with bold textures, such as bergenia or hens and chicks, in the foreground of your slope and position fine-textured plants, such as candytuft or dianthus, to the rear, the optical illusion that you created will make the area appear larger and more expansive.

If you reverse the combination of textures, the hill will actually look less steep than it actually is. You can actually create the same optical illusion described above, by combining plants with warm and cool colors. Warm colors advance and cool colors recede. For instance, if you set plants with blue-green foliage, such as hostas, or blue flowers, such as ageratum, at the back of a bed, or at the top of a hill, the blue colors will blend into the sky at the horizon line, causing a bed to look deeper than it actually is, and it will also cause a hill to appear greater than its height. If you want to make the hill look shorter, put plants with ruddy foliage, such as barberry, or plants with yellow, orange, or red flowers, such as rudbeckia or daylilies, toward the front of the planting.

Use plants with highly visible, upright, straplike foliage, such as ornamental grasses and daylilies, to their best advantage. They contrast handsomely with creeping juniper and other spreading shrubs. Also keep in mind that some vines make good ground-cover plants, particularly clematis and honeysuckle.

Another point to ponder is how you'll handle the inevitable transition area, where the plant textures and heights change, which occurs at the bottom of the slope where the ground-covers merge with lawn grass or some type of garden bed. Because the area at the base of a slope is often moist and well endowed with organic matter, it's an excellent place to grow perennials that form a low hedge, such as hardy geraniums, rudbeckia, or even ground-cover roses, which have been bred to have a low, spreading habit and to bloom intermittently.

Planting Ground-Covers on Slopes

It's frustrating to cultivate the erosion-prone soil on a slope. Taking a gentle approach is the best idea. Clean away existing vegetation by hand or smother it by covering the soil with black- or clear-plastic sheeting for two or three months, a process called solarization. If you cannot take the time to weed or solarize, kill the vegetation with a commercial herbicide, following label directions carefully (for information on safe usage and storing chemicals, see the maintenance chapter).

If there is insufficient topsoil on your hillside to plant in, you should spread as much good topsoil on it as necessary to form a smooth planting bed. Immediately plug in new plants, firm them in well, and apply a thick layer of straw mulch on the soil around the new plants. Straw is less likely to blow or wash away than other mulches, and it reduces evaporation while the plants are growing new roots. Irrigate as often as needed to keep the soil lightly moist for at least a month, or until the plants show signs of new growth. How do you know when a plant is established? New growth above ground usually reflects the development of strong roots below the soil. If you are in doubt, you can gently tug on the stems. A plant that is established resists being pulled out of the ground.

Keeping a Clean Carpet

Although mulch deters many weeds, a few always manage to gain a foothold. Weed plantings as often as needed for the first two seasons. After the first season, consider using an herbicide to control weeds, but read the label carefully to make sure the product is safe to use around ground-covers. After the second season, the plants should spread into a carpet that few weeds penetrate.

Maintenance is easy. In spring, use a balanced, con-trolled-release fertilizer, remove debris, and renew gaps in the mulch. In time, the plants will weave into a community that is naturally care-free.