Is your lawn looking a little tired and bare? If so, don't worry—fall is a great time to rejuvenate it. The weather is good for seed germination and competition from weeds is at its lowest. Here's how to seed your lawn to thicken it. Start by loosening compacted soil to stimulate growth.
Many patchy lawns suffer from compacted soil, which deprives grass roots of needed oxygen. Removing plugs of soil with a core aerator (rent at tool rental, garden supply or hardware stores) allows air and water to penetrate the ground and leaves space for surrounding soil to expand and loosen. Plan ahead and reserve the core aerator for at least half a day for an average-size lawn. It's best to use the aerator when the soil is moist. You'll need a truck or trailer to haul the core aerator home. The machine weighs 150 to 200 lbs., so it takes some muscle to move around. If you're not up to the task, consider hiring a lawn service for this part of the job (it may not cost much more than renting the aerator). Allow a day between aerating and seeding to let the soil plugs dry. Dry plugs will break up easier when you blend them in along with the dressing of topsoil.
Pick a grass seed mix that fits your climate as well as soil and shade conditions. There are many great sources of information. Check online, call your local county extension office, or ask at a local nursery for advice. Make note of your soil type, whether it's heavy clay or well-drained loam, and how much sunlight the area gets. Pick seed that's meant to grow best in these conditions and in your climate.
Measure your lawn and buy only half as much seed as you would if you were seeding. For small areas, throw out the seed as if you were feeding birds. For larger areas, use a drop spreader or broadcast spreader. Divide the seed in half and apply it in two passes at right angles to each other. Set the spreader for half the recommended application rate, or to about 20 percent open if there are no settings, and spread the first half of the seed. Keep a close eye as you're applying it so you don't run out. It's better to err on the side of spreading it too thin at first. You can always go over the area again.
The final step in the renovation is to cover the seed with a thin layer of soil. Buy bags of soil from the nursery for small areas. If you're reseeding an entire lawn, it'll be more economical to order topsoil delivered. Call a nursery or landscape supply company and say you want screened and pulverized black dirt for top dressing your lawn. You can also use dry, screened soil from your yard. One cubic yard of soil will cover about 1,300 sq. ft. at 1/4 in. deep. Spread the soil and rake it to create a thin, even layer over the seeds.
Lightly water the seeded area two or three times a day for 5 to 20 days until the seed sprouts. As the grass reaches 1 to 2 in. tall, water once a day, but leave the sprinkler on long enough to wet the roots, which are 1 to 2 in. deep. You can mow the grass when it's about 3 in. tall.