Establishing a lawn from seed is often difficult, and failure is usually due to improper irrigation. However, once your lawn is growing well, it's essential that you time your first mowing correctly. To grow a healthy, thick and weed-free lawn, keep your lawn mowed at an ideal height using a mower that has sharp blades. Also, avoid mowing when temperatures exceed 90 degrees F, and when the ground is extremely wet when you might cause ruts, especially for a new lawn.
Keep your lawn moist until the first mowing, paying careful attention on hot, dry and windy days. Newly-seeded lawns often need ¼ an inch of water a day to keep them moist.
Mow the grass when it is 3/4 inch higher than your desired height. For instance, if you want to keep your grass at 2 inches, wait until it reaches 2 ¾ inches high. Lawns kept between 2 to 3 inches in height grow thicker and have less weeds.
Mow your grass in rows. After the first mowing, mow no more than 1/3 of the height of the grass at a time. For example, if you keep your grass at 2 inches, mow by the time the grass reaches a height of 3 inches.