Hillside gardens face challenges which are common to all gardens. For instance, the planting plan should be compatible with the existing environmental conditions and there needs to be rich, fertile soil in which to plant. The difference is in the need to stabilize the garden soil. Though hillsides are subject to erosion problems, a well thought out garden design can help prevent soil runoff.
The direction the slope is facing plays an important role when determining which plants are most appropriate for your garden. South and west facing slopes receive more sun and are prone to dry conditions. As a result, plants that are tolerant of dry conditions are most suitable. On the other hand, slopes which face north or east receive less sun and subject to wetter soil. Here, plants which are tolerant of some shade and moist soil are ideal.
A plant's roots are very effective in holding soil in place on a slope. Most hillsides can be made relatively stable with plants, even shallow rooted groundcovers, such as ajuga and lily-of-the-valley are effective in preventing topsoil erosion. Studies show that a well designed hillside garden which incorporates native plants are quite successful when trying to prevent erosion. Plantings on a hillside should be diverse with a mix of groundcovers, shrubs, trees, and perennials. Utilizing a diverse mix of plants creates layers of vegetation which will help reduce the force of rainfall hitting the ground.
When planting a hillside garden, employing proper planting techniques is essential. The best solution to planting a successful hillside garden is to create terraced planting areas. Creating flat terraces suitable for planting helps prevent runoff and allows rainfall to seep into the soil.
To create a terrace, dig straight into the slope at a 90-degree angle. The soil which is removed can be spread around the downward part of the slope creating a larger terrace in which to plant. A retaining wall of boulders and large stones may be required to hold the soil above the terrace in place. Creating this flat planting area makes watering more efficient. Rather than flowing down the hill and forming gullies, rainwater and irrigation has a chance to penetrate the garden surface.
Larger trees and shrubs which are planted in the hillside garden will need a well constructed around their base. Created with displaced soil and mulch, they’ll hold water and should be as wide as the tree's canopy. They should be stronger on the downhill portion as this is where water will want to flow. Test out your well by filling it with water. Strengthen any weak spots with more soil and mulch.
A creative way to stabilize a small slope is to plant a rock garden. Rocks and stones placed on the slope can prevent erosion and add interest to the hillside. Small pockets of soil can be created around the rocks for planting perennials and shrubs.
Consider using soaker hoses for irrigating hillside gardens. They release water into the soil slowly and over a long period of time. As a result, plants are watered deeply and thoroughly. Avoid drastic re-grading around existing trees and shrubs. Both exposing a plant’s roots and building up around its trunk with soil is potentially harmful. When planting a hillside garden start at the top and work your way down the slope. Its easier and better for the plant as they are less likely to be steeped on.
With thoughtful planning and design a sloping yard can be transformed into a stable and beautiful hillside garden.