The immediate task after scattering grass seed is to provide a protective layer that secures the seed and cultivates an environment conducive to germination. Selecting the appropriate covering material directly impacts the success of a new lawn by safeguarding vulnerable seeds from environmental factors and pests. This protective step ensures the seed absorbs the moisture and energy needed for initial growth.
Why Covering Grass Seed Is Necessary
Covering grass seed serves three main functions required for successful establishment.
The first is maintaining consistent soil moisture, necessary for the seed to initiate germination. Without a cover, the tiny seeds and surrounding topsoil can dry out rapidly, halting the growth cycle and leading to seed death.
A second function is preventing erosion and displacement caused by wind or rain. A protective layer absorbs the impact of heavy raindrops and anchors the seed to the soil, ensuring it remains in place to develop a root system.
Finally, the covering acts as a physical deterrent, shielding the seeds from being consumed by birds and other small pests. By mitigating these threats, a covering material maximizes the number of seeds that successfully transition into seedlings.
The Best Material Choices
The most widely used material for covering newly sown grass seed is clean straw mulch, derived from the dried stalks of cereal grains like wheat or oats. Straw is valued for its low cost and its ability to create a light, breathable barrier that retains moisture and moderates soil temperature fluctuations. Since the grain seed has been removed, straw is typically free of unwanted weed seeds, preventing the introduction of invasive plants to the new lawn.
An alternative popular option is sphagnum peat moss, recognized for its exceptional capacity to hold water—up to 20 times its own weight. Applying a thin layer significantly enhances moisture retention, useful in warmer climates or on sandy soils that drain quickly. Peat moss changes color when it dries, making it easy to identify when the seeded area requires more water. However, peat moss is naturally slightly acidic, which may benefit certain grass types but could necessitate a soil pH test beforehand.
Screened compost is an organic choice, as it not only protects the seed but also introduces nutrients and organic matter to the soil as it decomposes. When choosing compost, ensure it has been finely screened to remove large clumps that could bury the seed too deeply or prevent water penetration. Compost helps improve the overall structure of the soil, promoting better aeration and root growth for the emerging seedlings.
For large areas or challenging terrains, commercial seed coverings, often referred to as hydromulch, are available. Hydromulch is a slurry of water, fiber mulch, fertilizer, and a tackifier—a binding agent that secures the mixture firmly to the ground. This method is effective for slopes where erosion is a concern, as the tackifier minimizes wash-out and keeps the seed-to-soil contact intact. The dyed fiber in the slurry provides uniform coverage, shielding the seed from wind, sunlight, and pests.
Proper Application Techniques and Depth
The application of any covering material requires a delicate balance, as applying too much can smother the tiny seedlings and prevent sunlight from reaching the soil.
For straw mulch, the goal is to obscure approximately 50% of the soil surface, often called the “50% rule.” This light layer provides protection and moisture retention while allowing sufficient light penetration for the grass to photosynthesize once it germinates.
To apply straw correctly, bales should be “fluffed” and lightly scattered by hand, ensuring the material is thin enough for the ground to still be visible through the covering. After application, the straw can be gently patted down with the back of a rake or a light roller to settle it against the soil surface. This compression helps anchor the material and improve seed-to-soil contact without compacting the underlying soil.
When using finer materials like peat moss or screened compost, the layer must be extremely thin to avoid burying the grass seed too deeply. The maximum recommended depth for these materials is between 1/8 and 1/4 inch. A layer thicker than 1/4 inch risks forming a hard crust when dry, which can inhibit emerging shoots from pushing through to the surface. A light raking or dragging of the surface after application helps integrate the material with the seed and topsoil, ensuring good contact for moisture absorption.
Materials That Hinder Germination
Certain materials commonly found around the home or garden should be avoided when covering grass seed because they impede successful germination.
Non-certified hay, which is distinct from clean straw, contains the entire flowering body of the grass plant and is full of weed seeds. Using hay will introduce undesirable plants like alfalfa or various grasses into the lawn, which will compete with the newly sown turf for resources.
Applying a thick layer of heavy topsoil or sand is counterproductive. Grass seeds should not be buried more than 1/4 inch deep; a thick layer of soil prevents light from reaching the seed and requires the emerging shoot to expend too much energy to reach the surface. Furthermore, heavy topsoil can easily compact when watered, creating an impenetrable barrier that restricts air and water movement.
Plastic sheeting or tarps, while effective at retaining moisture, should not be used as a grass seed cover. These materials create a greenhouse effect that can rapidly raise the temperature underneath to dangerous levels, essentially “cooking” the new seedlings. The excessive humidity trapped beneath the plastic also creates an ideal environment for fungal diseases to develop, which can quickly wipe out the young grass.