Do I Need Straw or a Blanket on Grass Seed?

The key to starting a lawn successfully from grass seeds is to keep the seeds in place until they take root and begin to grow. This seemingly simple task is fraught with perils, however, such as hungry birds that can't resist the buffet of seeds spread before them, strong winds that displace the seeds and heavy rains that wash the seeds to the bottom of a sloped lawn. You can give the grass seeds you sow a fighting chance by mulching them with straw or hay, or by covering them with a specially made botanical blanket.

Although the words "hay" and "straw" are used interchangeably in the gardening world and those plant products look surprisingly similar, they are not the same. Both are sold at plant nurseries and garden centers in rectangular bales, but look closely to see a significant difference between the two -- the presence of seeds.

Hay is pasture grass, typically used for livestock feed and forage. Although grass is usually cut for use as hay before the grass goes to seed, it's often left growing in the field until some seeds have formed. Typically, hay contains more seeds than straw, and the seeds are unwelcome additions to the grass you're trying to grow.   

Straw is the dried stalks of grain plants -- what's left after the seed heads -- grains -- have been removed. Some seeds may escape the grain-harvesting process and remain on the plant stalks, but true straw is virtually seed-free.

You can use either straw or hay mulch to cover grass seeds. If, however, you want to kill seeds that may be in the straw or hay, purchase straw or hay bales two weeks before you plan to sow grass seeds. Then use a process called "solarization" to kill any seeds in the bales: Cover the bales with clear plastic, tucking the plastic's loose ends underneath the bales, and place the bales in full sun. After two weeks, the sun's heat will have killed all or most of the seeds.

Loosen the straw or hay in a bale by separating it into "sheets," and shake it over newly sown grass seeds. Your goal is to cover 50 to 75 percent of the ground without applying the mulch as a solid mat across the seeded area. 

Remove one-half of the mulch when the grass is 2 inches tall. The remaining straw or hay will decompose in place.

One bale of straw or hay that weighs 50 pounds should cover about 1,000 square feet of lawn.

Don't raid your linen closet for a spare blanket to cover grass seeds. The type of blanket needed is called a "germination blanket" or "erosion-control blanket." The blanket is not embedded with seeds; it covers an existing seeded area. You can use the blanket if your yard is level, but the covering excels on slopes and hilly terrain, keeping grass seeds from washing downhill during rainstorms. The blanket is porous to allow sunlight and water to reach the seeds underneath it.

Degradable: Some germination blankets are biodegradable. This means that living organisms, such as bacteria and other soil organisms, will feed on the blankets' materials and decompose the blankets over time. Other germination blankets are photodegradable, which means they will decompose in the presence of sunlight. Some germination blankets are both biodegradable and photodegradable.

A benefit of degradable germination blankets is that you simply leave them in place, even after grass seeds germinate.

Synthetic: Some germination blankets are made of synthetic materials, which do not decompose.

A benefit of synthetic germination blankets is that they are reusable, but removing them after the grass sprouts is necessary.

Germination blankets are purchased in rolls, which you simply unroll and lay loosely over a seeded area. Secure the blankets' ends with landscape pins -- U-shaped pins that you press into the ground.