Things You'll Need
You can thicken up a thin lawn by overseeding. Fall is the best time of year to overseed due to the warm soil, cool weather and lack of weeds. Plant the grass seed in the early fall so it has enough time to establish before the first frost. The best types of grass seed to overseed with are ryegrass, bluegrass or fescue. Test your soil before overseeding to determine if any underlying problem is causing your grass to die in the first place.
Mow the grass between 1-and-1/2 to 2 inches high. Stir up the soil in small areas with a metal rake. Be gentle enough that the area's growing grass is not ripped out. Use a core aerator in larger areas.
Pour the grass seed into a broadcast spreader. Set the spreading rate, following the manufacturer's directions. Push the spreader from right to left and then up and down over the area. Apply seed by hand in small areas. Scatter two to three handfuls over the dirt. Gently rake over the dirt with a metal rake to bury some of the seeds.
Water the overseeded area once to twice each day for seven to 10 minutes each time. Do not allow the soil to dry out. Maintain the growing grass's height at 1-and-1/2 to 2 inches with frequent mowing until the new grass reaches the same height. Then, maintain grass height between 2-and-1/2 to 3 inches.
Fertilize the lawn six weeks after seeding. Use 1 lb. of nitrogen fertilizer for every 1000 square feet of lawn. Pour the fertilizer into a broadcast spreader and set the spreading rate accordingly.
Use a slit seeder to overseed your lawn instead of a broadcast spreader.