Growing a Hillside City Garden

Challenges common to all gardening include getting good soil, adequate sunshine and water. The critical factor with hillside gardening is stabilizing the soil, so it's good to start with a plan.

Plant selection and diversity are key. Much like the netting you see along freeways that hold rocks in place, deep-rooted plants do a great job of holding themselves upright and keeping the hillside stable. But even shallow roots can work wonders at inhibiting topsoil from eroding (figures B and C). Hobens Feldt suggests using a little of both. Groundcovers, like shrubs and flowering perennials, are especially wonderful because they'll grow to capture the moisture and stop erosion.

Besides being smart about what they plant, hillside gardeners are also smart about how they plant. "The best way to make your hillside work for you is to terrace, and the way you do that is to literally trench and add," says Hobens Feldt.

"The most important issue with hillside gardening is to be able to keep the moisture where you want it—at the plants." With a cherry tree she planted, the wood chip mulch was washed away due to runoff, prompting her to create a "moat" around the plant.

Next, a thick layer of mulch—only on the lower (downhill) side of the plant—strengthens the moat. The area closest to the tree doesn't need to be mulched if it already has a natural surrounding leaf cover.

Another way to stabilize your garden is to incorporate rocks. Boulders can inhibit erosion because of their size and also add interest to the space. Little rocks shouldn't be underestimated; they can wall off dirt just as well (figure G).

If you have an extreme slope, you may have to take extreme measures to garden on the edge. It may involve major earth-moving or adding a retaining wall.

Whether you plant annuals or perennials on the hillside, make sure you use plants that are well suited for the environment. Having durable plants to begin with considerably increases your chances of success.