Establishing a new lawn requires applying a protective covering, or mulch, over freshly sown grass seed. This step is necessary for success, but the choice between straw and hay often causes confusion. Understanding the fundamental differences between these two agricultural byproducts is crucial, as selecting the wrong material can undermine the entire seeding effort.
The Purpose of Covering New Seed
Applying a light layer of organic material over new grass seed serves multiple purposes tied to successful germination. The primary benefit is moisture retention, as the mulch reduces water evaporation from the soil surface. This is important because grass seeds require constant moisture to break dormancy and sprout.
Mulch also regulates the temperature of the seedbed. The covering insulates the soil, preventing temperature fluctuations that can stress or damage emerging seedlings. Furthermore, the material acts as a physical barrier to control erosion, keeping seeds from being washed away by rain or scattered by wind. A thin layer also deters birds from consuming the seed.
Why Straw is the Recommended Choice
Straw is the preferred material because it is a byproduct of harvested grain, typically wheat, oat, or barley, consisting only of the dried, hollow plant stems. This material is lightweight and contains very few viable seeds. The grain heads are removed during the harvesting and threshing process, resulting in a cleaner product.
When applied correctly, straw allows approximately 50% of light to penetrate the soil surface, which is necessary for grass seedlings to photosynthesize and grow. It decomposes slowly, providing a stable, protective layer that does not form a dense mat over the emerging grass. This gradual breakdown also contributes organic matter to the soil as the new lawn establishes itself.
The Risks Associated with Hay
In contrast to straw, hay is composed of the entire grass or legume plant, such as alfalfa or ryegrass, cut and dried for animal feed. Because hay is harvested when the plant is mature, it contains a high volume of viable seed heads from the parent plants. Using hay as a mulch introduces these seeds directly onto the lawn, where they will germinate along with the desired grass seed.
This introduction of foreign seeds often leads to a weed problem, as the vigorous plants in the hay compete with and quickly outgrow the new lawn. Hay is also denser than straw and holds more moisture, which increases the risk of fungal issues or mold if applied too thickly. Using hay can turn a lawn project into a prolonged battle against unwanted growth.
How to Apply Mulch for Best Germination
To maximize germination success, the straw should be broken apart and scattered loosely over the seeded area immediately after planting. The goal is to achieve a thin, uniform layer that provides about 50% coverage of the soil surface. This coverage is sufficient to retain moisture and protect the seed without blocking sunlight or restricting seedling growth.
After application, the straw should be thoroughly wetted down. This is especially important if using an erosion control product containing a tackifier, which helps the material bond to the soil. The newly seeded area requires frequent, light watering to keep the seedbed moist, often multiple times per day. If applied thinly, the straw can be left in place to decompose naturally once the grass reaches two to three inches in height.