Planting grass seed in an existing lawn or turf is called overseeding. A homeowner will choose to overseed an existing lawn or turf for two reasons: to thicken or repair a lawn that is thinning out or damaged; or to seed annual grasses in areas where warm season grasses go dormant and turn brown in the fall season. For best results, overseed turf grasses in the fall, dormant season once the daytime temperatures drop below 70 degrees Fahrenheit.
Mow the current turf grass to a height of 1 inch. Use a bagger attachment on the mower to collect the cut grass or rake the lawn well to remove all grass clipping debris.
Aerate or de-thatch the lawn to remove compacted debris at the soil level. This will open up ground and allow the seeds to penetrate into the soil. Rake the area well after de-thatching to remove all debris that was pulled up from the ground.
Sow the grass seed using a broadcast lawn seeder that is pushed along the turf in straight lines. This will give an even covering of seed over the lawn. Apply slightly more seed than is recommended on the seed packaging to guarantee there is enough seed reaching the soil level for germination.
Rake the lawn after seeding to push seeds as close to the soil level as possible.
Water the overseeded lawn to moisten the entire area to a soil depth of several inches, being careful to not have standing water. Continue to water daily for one month or until the seed germinates and begins to grow.
Mow the overseeded lawn once the new grass growth reaches a height of 3 inches.
Water the lawn during dry periods when there is less than 1 inch of rainfall per week to prevent the lawn from drying out.