Lawns wear out over time and stop producing thick, healthy vegetation. After three or four years brown spots may appear, and soil may become visible in your lawn. These are signs that your lawn needs to be rejuvenated. Applying grass seed to your entire lawn is commonly referred to as overseeding, a process by which new seed is added to an existing lawn to thicken it and make it more lush and weed resistant. The best time to overseed varies by region, but early September is usually a good time, as the hottest part of summer has passed but the soil is still warm enough to germinate grass seeds.
Mow your lawn after putting your lawnmower on its lowest setting. The blades may scrape dirt occasionally, but that's OK. Attach a bag to catch the lawn clippings if you have such an attachment.
Rake your lawn thoroughly with a lawn rake or a thatching rake. The idea is to remove all old, dead grass and clean your lawn down to bare dirt. Scoring the surface of the soil with your rake will also help implant the grass seed.
Rent an aerator from your local nursery or home improvement center. Roll the aerator across your lawn in one direction, then repeat the process in the opposite direction. The aerator pokes holes in the soil, thereby increasing the seed-to-soil contact.
Rent a seed spreader (also available from your local nursery or home improvement center) to apply the grass seed that's appropriate for your lawn. Follow the manufacturer's recommendations for seeding a new lawn. If overseeding with Kentucky bluegrass, you'll want to use 2 to 3 pounds of seeds per 1,000 square feet. If you're using tall fescue, 6 to 8 pounds of seeds per 1,000 square feet should do the trick.
Use a fertilizer spreader to apply ¼ inch of starter fertilizer or screened organic manure on top of your grass seed.
Water thoroughly with a sprinkler by applying at least 1 inch of water. Keep the lawn moist but not soggy for the next 21 days. This may mean watering more than once each day depending on temperature and wind conditions.
Mow your lawn when it's 4 inches high, setting your mower for 3 or 3½ inches. Maintaining your lawn height at 3 to 3½ inches will reduce weeds and keep your lawn thick and lush.