Growing Grass on Slopes and Hillsides

sloped backyard

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If your property has a significant slope of 15 percent or more, you may think that grass is the best way to stop erosion. But turf may not be the best choice. Consider these points:

  1. It's difficult to keep the seed in place long enough for successful germination.
  2. Most turf grasses are shallow-rooted and not well adapted for challenging slope conditions.
  3. Hillside mowing is difficult. Mowing accidents occur on slopes, especially inclines more than 15 percent.
  4. If your mower doesn't have an oil pump, oil may not circulate properly during extended hillside operation. The lack of oil can ruin the engine.
  5. If you live in a fire-prone area, hillside grasses may pose a hazard. It can be hard to extinguish flames on steep areas. Fire-resistant shrubs and trees may be a better choice.

There are, however, many types of grass available; while typical turfgrass may not be an ideal option, there are some grasses that can make the grade.

Grass Selection and Planting Techniques

The best grass for your site will vary depending on your location. If the site is in the dry, warm areas of the United States, buffalograss (Buchloe dactyloides) is a good choice. The species has long roots, grows relatively slowly, requires less mowing than most grasses, and is drought tolerant.

For northern areas with more rain and cooler weather, consider a mix with a significant amount of creeping red fescue (Festuca rubra). This fescue is also good shade grass.

Deep-rooted "bunching" grasses work well on hillsides. Some top choices among these non-turf grasses include little bluestem (Schizachyrium scoparium), prairie dropseed (Sporobolus heterolepis), sideoats grama (Bouteloua ​curtipendula), blue grama, (Bouteloua gracilis), wavy hairgrass (Deschampsia flexuosa), and Indiangrass (Sorghastrum nutans).

When considering how to plant, see which of these ways is best for your situation:

  • If broadcasting seed into a newly prepared site with loose topsoil, mix the seed into the soil. Though this may require additional seed, mixing improves the chances that, even after some erosion, there will still be seed. Cover the hill with straw after seeding.
  • If the grade is less than 25 percent, a slice seeder may work. This equipment makes tiny slits in the earth and places the seed directly into the soil, not on the surface.
  • Consider hydroseeding, the practice of mixing the seed with a mulch slurry that adheres to the surface long enough to facilitate successful germination (this is also called hydraulic mulch seeding or hydro-mulching).
  • Look into "blanket seeding," which is securing seed with "blankets" made of various natural or biodegradable materials. Curlex blankets, for instance, hold the seed in place. Coir (shredded coconut) blankets do the same.
Man sowing grass seed on steep hill.
Kathleen Groll Connolly

Install Grass Plugs or Sprigs

Sometimes live plants are the best way to green up a hillside.

In the south, consider Bermudagrass, centipedegrass, or zoysiagrass, all of which are frequently started from sprigs or plugs. St. Augustine grass is almost always installed that way.

Grass "sprigs" are live roots that can be distributed into the soil with a rake. These have a higher success rate than seed on difficult sites since the plant is already alive. It can take about six months to one year to achieve coverage with sprigs, however.

Grass "plugs" are small plants, usually grown in trays of 36 to 72 units, with five-inch deep roots. When grass plugs are planted into the hillside, the success rate is usually much higher than with surface seeding. The expense is greater as well.

In northern climates, deep-rooted warm season and cool season grasses are often installed on hillsides from plugs.

St. Augustinegrass
Stickpen/Wikimedia Commons/Public domain

Shrubs, Trees, and Perennials

Keep in mind that turfgrasses are only one way to cover a steep hillside. Historically, nature would have covered steep areas with native trees, shrubs, or other plants. Relatively few grasses are adapted to hillsides. Consider a mixed planting.

Hillside in flower.
Kathleen Groll Connolly

Consider Terracing With Retaining Walls

Although it is a lot of work, long-term maintenance of a hillside will be easier if you perform some major landscape reshaping. One or more retaining walls built along the slope can convert a long, steep slope into a series of flat plateaus where small areas of flat, easy-to-care-for lawn can be planted. If they are large enough, these flat spaces can serve as recreational areas (such as a place for a patio or lawn swing), or you can turn this flat ground into gardens for vegetables or flowers.

High-angle view of water with adult men lying on retaining wall
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