When starting a new lawn or overseeding, protecting the newly sown grass seed is fundamental for successful growth. Applying a light covering, often called mulch, helps create a favorable microenvironment for germination. The most common materials used are straw and hay, but the distinction between them is often misunderstood. Understanding the specific properties of the covering material is important for achieving a dense, uniform lawn without introducing unintended problems.
Why Grass Seed Needs Protection
Grass seed is highly vulnerable to environmental factors once scattered onto the soil, making a protective covering beneficial for successful germination. The primary function of a mulch layer is to reduce moisture evaporation from the soil surface. This is important because grass seed requires consistent dampness, not just occasional watering, to successfully sprout. The covering helps maintain the necessary soil moisture levels for the seeds to complete germination.
A light layer of covering also provides a physical barrier against erosion and displacement. Heavy rainfall or routine watering can easily wash small seeds away or cause them to clump together. The mulch also helps deter birds and small animals from feeding on the seeds, improving the overall density of the emerging turf. The material helps moderate soil temperature, preventing extreme daily fluctuations that could stress the delicate seedlings.
The Critical Difference Between Straw and Hay
The decision between straw and hay is significant, as using the wrong material can compromise a new lawn’s success. Straw is the preferred material because it is the dry, hollow stalk left over after cereal grains like wheat, rye, or oats have been harvested. Since the grain heads are removed during harvesting, straw is considered a low-nutrient and mostly seed-free material. Its light, fluffy structure allows ample sunlight to pass through to the soil and emerging seedlings.
Hay, in contrast, is the entire dried plant—including leaves, stems, and seed heads—of grasses and legumes like alfalfa, clover, or timothy. Hay is harvested as animal feed, meaning it is packed with nutrients and contains a high volume of viable seeds. If hay is used, these foreign seeds will sprout alongside the desired grass, leading to an infestation of unwanted weeds and pasture grasses. These aggressive plants compete directly with the new turfgrass for water and nutrients, resulting in a patchy and uneven lawn.
Straw is the material of choice due to its low nutrient content and minimal weed seed contamination. Its composition allows it to break down slowly over time, adding organic matter to the soil without introducing invasive species. Hay’s tendency to introduce foreign seeds makes it a detrimental choice for any new lawn project. It is essential to ensure that any straw purchased is certified as weed-free to avoid introducing seeds from the grain crop itself.
Proper Application and Coverage Depth
When applying straw, the goal is to provide protection without creating a smothering layer. The most effective application involves a thin, light scattering that results in roughly 50 to 75 percent soil visibility. This transparency ensures that enough sunlight reaches the soil to promote healthy germination and growth of the grass seedlings. Applying the straw too thickly is a common mistake, as it can block necessary light and air circulation, suffocating the young grass sprouts.
To achieve thin coverage, pull apart the compressed straw bale into small, loose flakes before gently tossing them over the seeded area. After spreading, lightly patting the straw down with the back of a rake helps establish contact with the soil, preventing the material from blowing away. If applied correctly, the straw is designed to decompose naturally into the lawn as the grass grows, meaning removal is unnecessary. The straw is left in place until the new grass reaches a height of two to three inches, typically a few weeks after germination begins.
Commercial Alternatives for Seeding
For homeowners who wish to avoid traditional straw bales or are working on challenging areas, several manufactured alternatives are available. Erosion control blankets, often called seeding mats, are effective options for sloped areas prone to washout. These mats are typically made from biodegradable materials like straw, coconut fiber, or wood excelsior held together by netting. They are rolled out directly over the seed, providing stability and protection against heavy rain and wind.
Another popular alternative is peat moss, which is effective at retaining moisture and is generally weed-free. Peat moss is spread in a fine layer over the seed, but it can be more expensive than straw for large areas. It may also require heavier watering to prevent it from repelling water once it dries.
Specialized hydroseeding mulches or cellulose pellets are also available. These are often dyed green and contain a binding agent to lock the seed and mulch in place, offering a cleaner, more uniform appearance. These commercial products provide convenience and weed-free coverage, though they come at a higher cost than bulk straw.