Straw is often used to cover newly planted grass seed to reduce the amount of seed relocated by wind and water. Straw is preferred over hay because of its lower seed content.
Straw also holds moisture and keeps the grass seeds and seedlings from drying out. Until established, grass seed or plants will die if allowed to dry completely.
First Cutting of a New Lawn
Until grass seedlings are 2 to 3 inches in tall, they should remain covered by a straw mulch and foot traffic should be avoided. Grass seedlings will typically take from three to five weeks to reach this height, although it may be different depending on weather conditions.
Once the seedlings have reached this height, they are mature enough to handle light foot traffic and should be mowed for the first time.
Never remove more than one-third of the height of the grass in a single mowing. This is especially important for newly established lawns to prevent damage to the grass plants.
Always use a bag mower for at least the first few cuttings of a new lawn. Dried grass clippings can reduce sunlight and water available to the new seedlings, which can stunt their growth and root development.
Removing the Mulch
Prior to the first cutting, examine the straw mulch. If the original covering was light enough, the mulch will have begun to rot and may not require any removal other than gathering with the grass clippings from the first cutting.
If the mulch is heavier, remove it at this time with a garden rake, being careful not to damage the lawn. Heavy pockets of straw mulch can choke out new grass plants, and they may not be picked up with a mower bag. Be especially alert for thick clumps of rotting straw, as these can be especially harmful to grass seedlings.
Straw is preferred to hay as a grass seed mulch because of its lower seed content. Straw is made of the stems of grass plants, while hay contains the stem plus the flowers and seeds. Still, straw will contain some amount of seed from farm grasses and weeds. These plants are undesirable in a new lawn.
Removing the straw mulch from the grass seed sooner may lessen the amount of weeds that germinate, although most of the seed content has likely reached the soil in the first few days.
New lawns are often treated with weed treatment soon after being established. Check the weed killer manufacturer's instructions for recommendations.