When planting a new lawn or repairing bare patches, a common question arises regarding the need for a protective layer over the newly scattered grass seed. While grass seed can sometimes germinate on its own, a covering is generally a necessary step to ensure a successful and uniform establishment of the lawn. Applying a light layer of mulch or covering material creates a microclimate that significantly improves the seed’s chances of survival and healthy growth. The practice of covering the seed addresses several biological and environmental challenges faced by vulnerable seedlings.
Hay Is Not Straw
The confusion between hay and straw is a common pitfall that can severely compromise a new lawn project. Hay is material cut from grasses or legumes, such as alfalfa or timothy, while the plants are still green and contain their seed heads, making it primarily a feed source for livestock. Because hay is harvested before or during the plant’s flowering and seeding stage, a bale of hay is typically full of viable seeds from the original plant, as well as various weeds. Introducing this material onto a newly seeded lawn will essentially plant a competing crop of weeds and unwanted grasses alongside your turf seed.
Straw, conversely, is the dry, hollow stalk left over after the grain from crops like wheat, oats, or barley has been harvested and removed. This material is a byproduct of the grain industry and contains very few, if any, viable seeds, making it the preferred agricultural material for mulching new grass seed. Selecting clean straw, often labeled as “weed-free,” prevents the introduction of foreign plant matter that would compete with the desired turfgrass for water and nutrients. Using straw instead of hay is a distinction that can mean the difference between a lush new lawn and a patchy area full of undesirable plants.
The Necessity of Covering New Seed
Covering new grass seed fulfills several critical functions that dramatically increase the rate and consistency of germination.
Moisture Retention
One of the most important roles is moisture retention, as grass seeds require consistent dampness around the embryo to begin the germination process. A light layer of covering acts as a barrier, reducing the rate of water evaporation from the soil surface after irrigation or rainfall. This protective shield helps maintain the uniform moisture level necessary for the seed to sprout and establish its delicate first roots.
Erosion Control and Protection
The covering also provides control against environmental displacement and erosion. Strong winds or heavy rain can easily wash away or scatter tiny grass seeds, leading to uneven growth and bare spots in the lawn. A thin layer of straw or mulch holds the seeds and surrounding soil particles in place, absorbing the impact of water droplets and breaking the force of the wind. Furthermore, the physical barrier helps to deter birds and other small animals from feeding on the exposed seeds, protecting the investment in the new turf.
Temperature Regulation
A third benefit relates to soil temperature regulation. The mulch layer provides slight insulation that helps moderate the temperature of the seedbed, preventing extreme fluctuations that can stress or damage the emerging seedlings. A stable, moderate temperature creates a more favorable environment for the biochemical processes involved in germination and early root development. This stabilization is particularly beneficial during unseasonably warm or cool periods in the spring and fall planting seasons.
Alternative Seed Coverings
While straw is the traditional choice, several other materials offer similar benefits for covering newly planted grass seed.
Cellulose and Paper Mulches
Specialized cellulose or paper mulches are often sold in bags and are specifically designed for lawn seeding applications. These products often include a tackifier, a sticky agent that helps bind the mulch and seed to the soil, providing superior erosion control. They decompose quickly into the soil, eliminating the need for removal.
Peat Moss
Peat moss is another common alternative, and when applied very thinly, it can assist with moisture retention, especially in small patches. However, it must be used sparingly, as a thick layer can form a crust that inhibits the emerging grass seedlings and prevents water penetration.
Erosion Control Blankets
Erosion control blankets or turf establishment mats made of biodegradable materials offer the most robust protection, particularly on slopes or challenging terrain. These blankets are pinned to the ground and provide excellent moisture retention and stabilization until the grass is fully established.