Hillside Landscaping: Smart Solutions for a Sloped Yard

Protect your soil with designs that combine beauty and practicality.

Moderate to steep slopes require special planting and care. Imagenet/Shutterstock

Hillsides, slopes, and otherwise uneven yards are some of the most challenging of residential designs. Sloped yards are subject to erosion from wind, rain, and even installed irrigation, which may run off before it’s absorbed by the ground. That leads to another difficulty: Sloped areas tend to be drier than the rest of the property, with the caveat that sometimes the bottom of a slope can be extremely wet from all the runoff from above.

These steep surfaces can be difficult to mow, weed, and otherwise care for. But with the right strategies, you can stabilize and enhance sloped yards to prevent erosion, improve drainage, and create a visually appealing landscape.

The first step is to determine the amount of rise over run. For example, one foot of rise every 10 feet is 1:10, or 10 percent.

The good news is that gentle slopes below 5 percent, or one foot of rise for every 20 feet or more, don’t need special care. Moderate slopes from 8 percent to 16 percent (1:12 to 1:6), however, require special planting, while steep slopes above 20 percent, or 1:5, require significant design considerations. When a slope reaches 30 percent (1:3), it is deemed too steep to mow, with hillsides of 50 percent (1:2) being the steepest that can support plant life. Some larger properties may have a combination of elevations.

Plant Partners

Plant roots hold soil and soak up rainwater, while their above-ground growth acts as a barrier to mitigate slope runoff down the slope. Creeping juniper is a popular low-lying, low-maintenance ground cover for taming steep slopes, combating erosion, and preventing weeds.

Other top choices—whose deep roots hold soil in place and don’t need to be regularly pruned to look good—include ground cover roses, honeysuckle, Russian sage, bougainvillea (which is particularly drought tolerant and flowers best in dry conditions), spirea, burning bush, hydrangea, fragrant sumac, flowering quince, Japanese yew, snowberry, and fountain grass, to name a few. Gardeners in fire-prone areas may want to consider Mrs. Beard creeping sage, Bee’s Bliss sage, Pigeon Point coyote bush, Dana Point buckwheat, and John Dourley manzanita.

Be sure to check the plant labels for what’s best for your USDA agricultural zone.

Or simply go native and utilize easy-care indigenous grasses, ground covers, shrubs, vines, and even some trees to enhance visual appeal with varied height, colors, and texture. There’s strength in numbers, so plant as densely as possible while allowing for future growth and use a variety of species. Staggered placement can further obstruct runoff.

For particularly rocky or otherwise difficult soil or extreme slopes, it may be best to start with small plants in four-inch pots or even plugs and allow them to grow in. Even seeds work, particularly if you want to start a pollinator or wildflower garden in a wet area at the bottom of the slope.

Creeping juniper is a popular low-lying, low-maintenance ground cover for taming steep slopes, combating erosion, and preventing weeds. Peerachai Chaiprasut/Shutterstock

Temporary Assistants

Short-term erosion control systems keep the soil stabilized during construction or even for the first few years while plants get established. These can include biodegradable coconut coir logs, or long straw or fiber tubes called “wattles” that break up the flow of water down the slope. Stake them into place if needed.

Erosion control blankets (ECBs) made from biodegradable straw, curled wood fibers (aka excelsior), and coconut coir are another handy method of temporary soil protection and erosion control, and all work well for large areas or extreme slopes. Even loose mulch such as straw or wood chips placed between plants will work. However, don’t use loose straw for large areas, as it can blow away.

Boulders and Berms

Large boulders not only add an elegant aspect to a landscape design but also slow down and can redirect runoff. Carefully placed rocks, bricks, or timber can also be used to slow and redirect the water flow. These may be of particular importance if your home is at the bottom of the hillside or slope.

Another way to route water away from the home and other structures is to build berms—a fancy term for a mound of soil. Use a garden string or hose to plan how water should be diverted. A 2:1 ratio of width to height is a good start when planning. Once the design is chosen, layer soil and compost to provide nutrients for the coming plants, being sure to compact each layer. This can be as simple as stepping on it, to reduce settling later and then planting. One of the short-term erosion control systems previously mentioned can increase the new construction’s stability.

Carefully placed rocks, bricks, or timber can also be used to slow and redirect the water flow. Bespaliy/Shutterstock

Hidden Control

Slope grids offer a discreet, long-term solution, particularly for badly deteriorated slopes. A plastic 3D mesh of interconnected cells can be laid over the existing soil, filled with soil, and planted, or it can be used to xeriscape with decorative stones. They are typically available in four- to six-inch depths and provide significant protection against water and wind.

Erosion control blankets last between three months and three years, and stabilize the soil so that grass can grow. Lost_in_the_Midwest/Shutterstock

Terracing Tips

Adding retaining walls to a slope makes the most of it by making the levels accessible while stopping water from racing downhill.

Tiered Garden

One of the easiest ways to terrace a low-to-moderate slope is to build a series of raised planter beds out of ground contact-grade wood. Lay out the design with a hose or garden string. Keep the beds the same height and width/depth for visual appeal. Consider building wooden steps in the middle for easier access.

Stone Solution

Retaining wall blocks are a step up in sophistication and durability—but also in cost. Be sure to bury the first row of blocks to at least half their height. This involves not only digging a trench but also compacting it with a tamper or vibrating plate compactor to create a stable base.

Go Pro

For large, labor-intensive projects, including those with steep slopes of 20 percent or more, you may want to consider hiring a contractor who can accurately determine the slope and run of the hill, bring in a crew with heavy equipment, and install a hidden drainage system if needed.