Planting grass on a slope presents unique challenges because standard lawn establishment methods fail to account for gravity and water flow. The primary difficulty is preventing erosion—the washing away of newly applied seed and topsoil during rain or watering—and ensuring seeds can anchor effectively. Specialized techniques are required at every step to stabilize the planting surface and promote successful germination and root development.
Preparing the Surface for Seeding
Soil preparation is fundamental to anchoring the future lawn and differs significantly from preparing a flat area. Before seeding, assess the existing soil quality, ideally through a soil test, to determine if amendments like compost or fertilizer are necessary. Adding two to three inches of quality topsoil or organic compost improves soil structure, encouraging better water infiltration and stronger root penetration.
A crucial technique is scarification, which involves lightly disturbing the surface to create texture rather than a smooth finish. Raking across the slope creates small, horizontal grooves or pockets that trap grass seed and slow down water movement. For steeper inclines, minor terracing or constructing shallow perpendicular trenches can break the slope’s continuous run, significantly reducing water runoff velocity.
Selecting and Applying Seed on Inclines
Selecting the right grass variety is important for long-term erosion control, aiming to establish a dense, deep-rooted system that holds the soil in place. Tall fescue is highly recommended due to its robust root structure and drought tolerance, making it excellent for stabilizing embankments. Other options include perennial ryegrass for rapid establishment, or warm-season varieties like Bermuda grass or Buffalo grass in appropriate climates.
Slopes require a higher seeding rate than flat areas due to the increased risk of seed washout and uneven distribution. Apply the total amount of seed in two passes: half while walking up and down the slope (vertically) and the remaining half while walking across the slope (horizontally). This cross-hatching method maximizes seed-to-soil contact and ensures uniform distribution. For very large or steep slopes, hydroseeding offers a professional alternative where a slurry of seed, fertilizer, mulch, and water is sprayed onto the surface, providing immediate erosion protection and moisture retention.
Securing the Seed Bed with Erosion Control Materials
Securing the newly seeded surface is essential for preventing erosion and is required for all but the gentlest slopes. This protection is achieved using erosion control blankets (ECBs) or mats, which are laid directly over the seedbed to hold the soil and seed in place until the grass roots establish. These blankets are made from various biodegradable materials like straw, excelsior (curled aspen wood fibers), or a straw/coconut fiber blend, often held together by netting. The choice of material depends on the slope’s steepness and the required lifespan.
Single-net straw blankets are suitable for moderate slopes and short-term projects, while double-netted excelsior or straw-coconut blend blankets offer superior stability for steeper grades. Proper installation involves unrolling the blanket from the top of the slope downward, ensuring continuous contact with the soil surface to prevent water from flowing underneath.
The blanket must be firmly secured using landscape staples or pins driven into the ground at regular intervals, typically every five to seven inches along the edges and seams. The top edge of the blanket should be buried in a small trench, known as a check slot, to prevent water from entering between the blanket and the soil at the crest of the slope. Staking keeps the blanket taut against the soil, minimizing movement and promoting germination.
Post-Planting Watering and Care
Watering a seeded slope requires a modified approach to prevent the water itself from becoming an agent of erosion. Instead of a single, long soak, water the area using frequent, short cycles to keep the top layer of soil consistently moist without causing runoff. Use a fine mist setting on a hose or place a soaker hose near the top of the incline; this allows gravity to assist with moisture distribution without creating destructive channels.
Once the grass is established, deep, infrequent watering promotes the deep root growth necessary for long-term stability. The first mowing should be done at a slightly higher height than a flat lawn, as this protects the delicate new grass crowns and shields young roots from excessive sun exposure. Continually monitor the slope for small washed-out areas, and immediately reseed and patch the erosion control material to prevent minor issues from becoming major problems.