What Are the Functions of Straw on Planted Grass?

Weather Factors

• While grass seed needs water and sunlight to germinate, too much of either can be a bad thing. Heavy rains can quickly wash grass seed away, pooling it into lower-lying areas where it will sprout very thickly while leaving other spots as bare as they were before they were seeded. Long hours of direct unfiltered sunshine can also bake and dry out the seeds before they have a chance to sprout.

Functions

• A thin layer of straw mulch applied over the lightly pressed down seeds creates the partial sunlight they need to germinate, and also keeps them in place during a rain storm or on a windy day. The mulch also minimizes evaporation and the need for frequent watering by holding on to moisture longer while the tender grass seedlings develop. As it decomposes, the mulch adds valuable nutrients to the soil, minimizing the need for additional fertilizers.

Benefits

• Grass seeds do not all germinate at the same rate, and mulch plays an important role during the process. The pieces of straw form a loosely interwoven barrier that remains in place for as long as is necessary. As the new blades of grass emerge, they lift the mulch, providing more shade and moisture retention for seeds that have not yet sprouted.

Considerations

• Straw is the preferred mulch for covering grass seed, as it is generally free of the seed heads usually found in field hay that introduce weeds into the lawn. It should be applied thickly enough so that the seeds and soil are still partially visible, as putting it on more thickly chokes the developing grass. A bale of straw spread to a depth of about 1/4 of an inch covers roughly 500 to 1,000 square feet of lawn. While mulch can be left on to thoroughly decompose, this may rob the new lawn of nitrogen used during the decomposition process. Removing mulch is best done gently by lifting it with a pitchfork when the grass is roughly 2 inches high.