The key to seeding and growing a healthy lawn is to achieve good seed-to-soil contact during planting. Slit seeders are excellent for gaining seed-to-soil contact, thus making these machines excellent for lawn-repair projects. A slit seeder essentially makes a slit into the soil and deposits the seed into the opening in the soil. Slit seeders meter seed dispersal at a predetermined rate. Slit seeding a lawn is easy and can be done with little preparation to the lawn.
Remove all weeds from the lawn. Spray your lawn with a selective broadleaf herbicide to get rid of broadleaf weeds and a non-selective herbicide to treat patches of grassy weeds. Follow the label's instructions on how soon you can seed your lawn after using the spray.
Mow your lawn at half the normal mowing height. This will stress the existing grass slightly, reducing its competitiveness and allowing the new grass seedlings to better compete for water, nutrients and sunlight. Till any bare areas to cultivate the soil.
Measure or estimate the size of the lawn area you need to slit seed. If you have a square-footage figure, you'll be able to calculate how much grass seed to purchase from the seed packaging.
Select the right grass seed variety. Try to choose a similar variety to your existing grass. For example, if you currently have a cool-season grass species, choose another variety of cool-season grass seed instead of mixing with warm-season grass seed. Also look for grass seed varieties that are disease-resistant and require the appropriate amount of sunlight.
Rent or purchase a slit seeder. Slit seeders come in several varieties, mainly walk-behind units and tractor-mounted models. For a lawn, you probably won't need a larger tractor-mounted slit seeder. Make sure you read the owner's manual if you're purchasing a slit seeder or get operation instructions and tips from the store if you're renting one.
Make your first pass across the lawn with the slit seeder, applying half the desired seeding rate. Then, make a second pass perpendicular to the direction of the first pass, applying the second half of the seeds.
Soak the lawn thoroughly with water after seeding. Use a garden hose and ensure that all seeded areas receive water. Feed your lawn once per month with a commercial grass fertilizer, following the dosage instructions on the package.