When seeding a new lawn or repairing bare patches, the process involves more than simply scattering grass seed across the soil. Successful turf growth requires a protective and nurturing environment for the seed to begin its life. The choice of cover material is an important factor, significantly influencing the final outcome of your lawn project.
A cover material creates a stable microenvironment necessary for the seeds to transition from dormancy to active growth. Selecting the right covering directly impacts germination rates, moisture retention, and the overall health of the emerging seedlings.
Why Covering Grass Seed is Essential
Covering newly sown grass seed is a fundamental practice that optimizes conditions for successful germination. The primary function of a cover is to maintain a consistent moisture level in the top layer of the soil where the seeds rest. Grass seed needs constant dampness to break dormancy, and an uncovered seed can quickly dry out and fail if exposed to sun and wind.
The cover acts as a physical barrier, shielding seeds from erosion caused by heavy rainfall. A light covering also deters birds and small pests from consuming the seeds.
The covering provides temperature moderation, keeping the soil environment stable. The layer insulates the seeds from extreme temperature swings and harsh direct sunlight, promoting a steady germination rate. By keeping the seeds in place, the cover ensures good seed-to-soil contact, which is necessary for proper root establishment.
The Gold Standard: Recommended Organic Materials
The most traditional and widely used cover material is clean, weed-free straw, typically sourced from grains like wheat or oats. Straw is favored because it consists of hollow stems that create a light, airy layer, allowing sunlight to reach the soil surface while still retaining moisture. It also decomposes naturally over time, adding a small amount of organic matter to the soil without requiring cleanup.
Use straw (the dry stem of a harvested grain) rather than hay (the entire dried plant, including seed heads). Hay contains a high number of seeds from the forage grasses or legumes it is made from, which will germinate alongside your lawn seed, introducing unwanted weeds into your new turf. For the cleanest application, look for certified weed-free straw, as even traditional straw can occasionally contain weed seeds.
Peat moss is another common organic option, valued for its exceptional ability to absorb and hold water, which is beneficial for keeping the seeds moist. When applied correctly as a very thin layer, it can also prevent soil compaction and is generally free of weed seeds. However, peat moss can form a hard crust if allowed to dry out completely, which can inhibit the emerging grass seedlings.
Specialized Covers and Light Topdressings
For areas requiring greater stability, such as sloped ground, specialized engineered alternatives are available. Germination blankets, often called erosion control blankets, are netting-encased mats made from materials like straw, coconut fiber, or wood fiber. These blankets are particularly effective on hillsides because they physically hold the soil and seed in place, preventing washouts from heavy rain.
While highly effective for erosion control, some synthetic netting in these blankets may not break down easily and can require careful removal to avoid damaging tender seedlings. Biodegradable options with a short lifespan, such as those made with straw, are preferable for standard lawn applications, as they break down within about three months.
Another option is to use a light topdressing, which involves spreading a very thin layer of screened compost or fine topsoil over the seed. This practice improves seed-to-soil contact and provides immediate organic matter and nutrients. The layer should be minimal, about one-eighth to one-quarter inch thick, just enough to cover the seeds without burying them. Using a specialized seed accelerator mulch, which often includes paper mulch and a tackifier, is a convenient, weed-free alternative that darkens when wet, providing a visual cue for when to water again.
Application Techniques and Common Mistakes
Proper application is just as important as the material choice to ensure the cover does not smother the emerging grass. When using straw, the layer should be sparse enough that you can still see approximately 50% of the soil underneath. A general application rate for straw is about one 80-pound bale per 1,000 square feet, which provides the necessary light coverage without blocking sunlight.
After spreading the seed and the covering material, it is beneficial to lightly press the area with a lawn roller or tamper. This action ensures firm seed-to-soil contact, which is necessary for the seeds to absorb water and establish roots. Once the cover is applied, the area must be kept consistently moist with light, frequent watering, avoiding heavy saturation that can cause the seeds to rot.
A common mistake is applying the cover material too thickly, which can prevent light and air from reaching the seeds, leading to suffocation and poor germination. The straw should remain in place, as it will naturally decompose or be broken down by the first few mowings. Raking it up risks pulling out the delicate new grass seedlings.