If your property has a significant slope of 15 percent or more, you may be considering planting turfgrass on your lawn as a method of stopping erosion. However, seeding turfgrass may not be the easiest or the best choice.
Not only it is difficult to keep grass seed in place long enough for it to experience successful germination, but most varietals of tuft grasses are shallow-rooted and therefore not well adapted to the challenging conditions a slope may present.
Additionally, mowing on a hill is difficult and can actually cause damage to your mower (if it doesn't have an oil pump, the oil may not circulate properly during an extended hillside session, which can ruin the engine).
All that considered, you're not completely out of luck—while traditional turfgrass may not be the ideal option for your property, there are several grasses that can thrive in that exact area.
The best grass for your site will vary depending on your location. If your land is in a dry, warm area of the United States, buffalo grass 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 mixture that boasts a significant amount of creeping red fescue. It makes for a great shade grass, and is equally as attractive mowed and unmowed.
When considering how to plant your hillside grass, there are several methods that could work—the best depends entirely on your specific landscape and situation.
If you're broadcasting seed into a newly-prepared site with loose topsoil, simply mix the seed into the soil. Though this may require additional seed, mixing the two together improves the chances that, even after some erosion, there will still be seed. Cover the hill with straw after seeding.
If the grade of your landscape is less than 25 percent, a slice seeder may work. The tool, which almost looks like half a push mower, makes tiny slits in the earth and places the seed directly into the soil, not on the surface. This can help the roots of the grass to establish themselves stronger and deeper into the soil, making it more likely they'll last through inclement or unseasonal weather.
Really difficult landscapes can benefit from "blanket seeding," which secures seeds to the ground using "blankets" made from various natural or biodegradable materials, such as curlex or coir. That way, the seeds are held in place long enough to successfully germinate and establish without being disturbed.
Live Plant Options
When in doubt, sometimes live plants are the best way to green up a hillside. Varietals like bermudagrass, centipedegrass, or zoysiagrass are all frequently started from sprigs, a method in which live roots are distributed into the soil using a rake. They have a higher success rate than seed on difficult sites since the plant is already alive. Keep in mind, it can take about six months to one year to achieve coverage with sprigs, however.
Likewise, grass "plugs," also a common method, are small plants usually grown in trays of 36 to 72 units with five-inch deep roots. When planted into the hillside, grass plugs have a success rate that is usually much higher than with surface seeding—though the expense is greater as well. In northern climates, deep-rooted warm-season and cool-season grasses are often installed on hillsides from plugs.
Lastly, keep in mind that turf grasses and grass plantings are only one way to cover a steep hillside. Historically, nature would have covered those steep areas with trees, shrubs, or other plants. Consider a mixed planting of native trees or shrubs as an alternative to a grass-covered landing.
Terracing With Retaining Walls
Although it is a lot of work, long-term maintenance of a hillside property will be much easier if you perform some major landscape reshaping. By installing one or more retaining walls along the slope of your property, you can convert a long, steep hill into a series of plateaus, where small areas of flat, easy-to-care-for lawn can be planted. If they are large enough, these flat spaces can even 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.