What Do I Need to Do to Keep Grass Seed From Washing Away When Planting on a Hill?

Gravity is the enemy of gardeners who try to sow grass seeds on a sloped lawn or hilly area. The key to growing grass in these areas is keeping the seeds in place long enough for them to take root and "grab hold" of the slope before rain or irrigation water washes them downhill. By placing a barrier between the seeds and the water, you provide a shock absorber that buffers the water's impact and helps hold the seeds in place until they sprout.

Although commonly confused for each other, straw and hay are different. Hay is grass that is cut and dried, and straw is the stalk that remains after the seed heads of grains are harvested. You can use either as a mulch to cover grass seeds, but straw has a bit of a benefit: Typically, it doesn't contain as many seeds as hay, which means less competition for the grass seeds you sow. After sowing grass seeds and raking them into the soil, apply enough straw or hay to cover 50 to 75 percent of the ground.

A 50-pound bale of hay or straw typically covers 1,000 square feet when used as mulch over grass seeds.

You can cover newly sown grass seeds with burlap. The open mesh of the burlap allows air, sunlight and water to reach the grass seeds while cushioning the direct impact of rain or irrigation water. Lessening that direct impact helps stabilize the hill against eroding soil so the grass seeds don't end up at the bottom of the hill. Secure the burlap's loose ends with purchased or homemade, U-shaped landscape pins, and remove the burlap as soon as the grass begins to grow.

Burlap is available in rolls at plant nurseries and garden centers.

Specially designed covers called "germination blankets" protect vulnerable grass seeds on slopes. These blankets are made of biodegradable or synthetic materials. Choose either type, depending on your preference; germination blankets made of biodegradable materials can be left in place after the seeds germinate, and germination blankets made of synthetic materials are removed after germination. Simply spread or roll a germination blanket over newly sown grass seeds, and secure the blanket's edges with landscape pins or staples. Germination blankets are not solid; they are made of permeable materials that allow sunlight and water through while keeping the soil at consistent temperatures to help germination.

An option to covering grass seeds on a hill is to use a slit seeder to sow the seeds. This walk-behind machine resembling a lawn mower drops seeds into shallow slits that it cuts into the ground and lightly tamps the soil over the seeds. Because the seeds are more firmly planted in the ground by the machine than when they're simply raked into the soil, they're less likely to wash downhill. As an extra measure of protection, mulch the seeded hill with straw.

Use a slit seeder only if the slope or angle of your hill is 20 percent or less.