Heat and drought, cold and pests, poor soil or pets can damage a thick green lawn and leave it thin, straggly, or completely brown and bare in spots. Determine the cause of the damage and implement a damage control plan before reseeding to ensure the trouble does not return. Then take the time to prepare the seedbed with aeration and soil amendments before seeding the gaps or overseeding the thin spots in a damaged lawn.
Remove dead grass from brown or thin areas with a thatching rake until bare ground is visible.
Determine the cause of your lawn damage in consultation with a local extension service office if the cause of the damage is unclear. Apply recommended insecticides according to manufacturer's directions if the damage is the result of insects
Mix 1 part of compost or composted cow manure with 1 part of top soil. Spread a 1/4-inch layer of the mix over the damaged lawn areas using a flat metal rake.
Aerate the damaged areas of the lawn with core aerator. The entire lawn could be aerated if you choose.
Water the damaged lawn areas with the hose, or set a sprinkler over larger areas for an hour.
Spread a grass seed mixture over the damp topsoil/compost mixture at the seeding rate recommended for the seed and soil conditions, usually about 20 seeds per square inch if seeding by hand, or about 4 to 5 pounds of seed per 1,000 square feet of lawn. Do not plant the seeds too densely and use a lighter hand when over-seeding thin lawn areas that have existing grass
Rake over the seeded area with the flat metal rake to ensure good seed-to-soil contact. Water lightly with a hose or sprinkler, just enough to dampen the seeds but not enough to wash them away. Sprinkle a light, loose layer of straw over the newly planted seed.
Water lightly 2 to 3 times daily until the grass shoots begin to appear, then water daily until grass reaches 1 inch high. Water weekly thereafter, including a liquid fish emulsion fertilizer applied through use of a hose-end sprayer, until grass reaches 3 inches high. Discontinue weekly fertilizer and begin regular lawn mowing and maintenance schedule.