Crab grass is a seasonal weed that affects lawns in midsummer. The weed is a low-growing variety of grass that grows in a dense carpet. It typically grows from seed and takes over your lawn in the hottest part of the summer when heat and drought conditions weaken grass and cause it to grow patchy. Fescue is a cool season grass that is often affected by crab grass due to its patchy growth during drought conditions. To make sure that fescue remains thick and does not give crabgrass a chance to become established, more fescue seed should be planted each fall.
Estimate how much of your fescue lawn has died over the summer to help calculate how much seed to replace the lawn with. Multiply that number by the establishment seeding rate of 5 pounds of seed per 1,000 square feet. For example, if your fescue lawn grass is over 50 percent dead, multiply that number by 5 pounds to come to a total of 2.5 pounds of fescue per square feet.
Mow your lawn to a depth of 1 inch tall. This will allow light to reach the seed.
Rake over your lawn with a slit seeder. A slit seeder makes ¼ inch gouges in your lawn and allows the seed to come in contact with the soil. Pass the rake over your lawn between two and four times, changing the direction that you rake each time.
Pour half of the seed into a broadcast spreader and push the spreader over your lawn to distribute the seed. Re-fill the spreader with the other half of the seed and make a second pass with the spreader, changing the direction that you push the spreader over your lawn by 90 degrees.
Water your lawn with a sprinkler up to four times daily with ¼ inch of water per square inch. Taper off watering your fescue lawn to 1 inch of water once every seven days once the grass seed has germinated.
Continue mowing your lawn to 1 inch tall until the new grass seed reaches this height, then raise the deck of your mower to 3 inches. Keep your grass mowed at 3 inches tall year-round to prevent crabgrass seed from germinating.