Grass seed is typically planted in freshly tilled soil. This soil should be kept moist and at a fairly consistent temperature, and spreading wheat straw over the newly planted grass seed can help with both these issues.

Also, the straw helps hide the seeds from hungry birds who can devastate your lawn before the seeds have a chance to germinate. When you are trying to grow grass on uneven or hilly ground, the straw can help reduce erosion and hold the seeds in place.