Mulch is recommended for new grass seeds for several reasons. Covering the grass seed with light mulch helps to lock the seeds in place and prevents their movement. Of all the material used as mulch, straw is the most widely used, according to David Mellor in "The Lawn Bible." The mulch on seeds keep them protected from predators likes birds and hungry critters. Mulch reduces chances of soil erosion and retains soil moisture.
Though straw is a widely used mulch material, the right type of straw needs to be used or it can prove more harmful than helpful. Obtain weed-free straw intended as mulch from a garden center. Straw bought from a farm is likely to contain weed seeds that will start to germinate with grass seeds and create problems by choking out the new grass. Certified weed-free straw is recommended as mulch for grass seed. Hay is not a substitute for good quality straw.
Straw is commonly sold in bales. A single bale of straw is about 35 to 50 lbs. This is sufficient for covering 1,000 square feet of lawn, the recommended rate as suggested by the University of Illinois Extension. Other experts such as the University of Vermont Extension recommend using a bale for 500 square feet of lawn. (
After the lawn has been seeded, use an empty water-ballast roller, or similar equipment, over the site to help increase seed contact with soil. Spread the straw over the soil in a very thin layer so that the soil below is visible. Avoid spreading in a thick layer as this will make it difficult for the seedlings to penetrate. The advantage of straw is that it does not have to be removed later and will gradually decompose. Do not attempt to rake off the straw as this can seriously damage new seedlings.