If your lawn looks patchy or goes dormant in winter, the solution may be to overseed your lawn. Overseeding will fill in grass in patchy lawns. Overseeding in the fall with cool season grass will provide year round color in transition zone lawns. The first step in overseeding your lawn is to remove the thick layer of thatch that has built up at the base of your lawn. Thatch is composed of grass roots, stolons, dead stems and other debris. A thick layer of thatch will prevent nutrients, water and oxygen from reaching the soil, which will prevent grass seed from becoming established.
Time seeding and dethatching for spring if you are overseeding with warm season grass, or in the fall for cool season grass.
Mow your lawn to its lowest recommended height, which is typically 1 to 1 ½ inches tall. This will allow light to penetrate to the soil line so that your new grass seed can sprout.
Position a dethatching machine at the starting point in your lawn where you want to begin dethatching. Set the machine's speed to slow initially and engage the clutch. Start the machine with a pull rope, similarly to if you were starting a lawn mower. Release the clutch and begin to push the dethatching machine over your lawn. Adjust the speed once you are used to the machine. Pass the machine over your lawn in sections similar to if you were mowing the lawn. Make a second pass over the lawn, varying your pathway by 90 degrees.
Rake up the debris left by the dethatcher. Bag it with lawn bags and discard it.
Aerate your lawn with a lawn core aerator. Lawn aerators may be rented from a heavy equipment store. They operate similarly to lawn mowers in that they start by pulling on a rope, and they are pushed in front of the operator. Set the core aerator to slow speed until you become used to its operation. Slowly push the machine across your lawn in sections just as if you were mowing the lawn. Repeat up to four times, changing the direction of the path that you walk each time. When you have finished, there should be between 20 and 40 core holes per square foot.
Spread grass seed over your lawn using a broadcast spreader. A broadcast spreader contains a holding tank for seed and a mechanism that scatters seed across a lawn as you push it in front of you. Pass over your lawn with a broadcast spreader up to four times, varying the direction in which you push your spreader each time. The seeds will sprout everywhere they come in contact with the soil through the aeration holes.
Water your soil to keep it moist and encourage the seeds to germinate. Use a quarter inch of water per one inch of soil up to four times daily to keep your lawn damp. Gradually decrease this frequency after the grass seed sprouts until you water with one inch of water every 10 days.
Continue to mow your lawn so that it is no more than 1 ½ inches tall until the new grass seedlings reach this height. Then raise the deck of your lawn mower to the recommended height for your new grass and allow it to reach this height.