Even if your lawn looks good, it's essential to plant grass seed again to rejuvenate the lawn and keep it lush and green. This is called overseeding. Very few homeowners do it, though it's an important lawn maintenance task. Grass slows down its growth after five or six years, allowing weeds to fight their way in. Overseeding every three to four years will keep your lawn looking thick and dense and help it resist disease.
Set your mower to the lowest setting. Mow the grass as close to the ground as possible, even if you're scraping soil. Collect the grass clippings.
Rake the area where you want to plant grass seed. Collect all debris leaving just bare soil and stubble. Grass seed needs to touch soil to root. It will not root if it's on top of grass clippings or other debris. The stubble you're leaving behind will keep the grass seed from being washed away in rain.
Follow the manufacturer's guidelines to determine how much land the box of grass seed will cover. There may be instructions for overseeding and seeding a new lawn. Follow the guidelines for a new lawn to get the thickest grass possible.
Spread the grass seed with a mechanical or hand spreader, depending on the size of the area you're overseeding.
Water the seed until moist but not soaking. Continue watering it at least twice a day to keep it moist. If you allow it to dry out, you can lose up to 30 percent germination. Follow this schedule for at least two weeks.