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What is overseeding a lawn? Seed, preparation and quote details
Overseeding spreads grass seed into an existing lawn, without tearing it out, to thicken thin turf and bring in newer grass varieties. A renovation kills or strips the old lawn first; overseeding keeps it. University of Maryland Extension's rate for tall fescue is 4 pounds per 1,000 square feet, sown in autumn. Ask how the seed will reach the soil (core aeration, slit seeding or raking) and who waters it afterward.
When is the best time to overseed?
Late summer into early fall for cool-season lawns. University of Minnesota Extension's preferred window is mid-August to mid-September, with early spring second best, just as the lawn greens up. University of Maryland Extension recommends overseeding cool-season lawns every autumn. Its guide says warm-season lawns such as zoysia and bermuda are not overseeded.
Fall works because the soil is still warm, the air is cooling and fewer weeds sprout to compete, which gives seedlings a long stretch before summer heat. Spring seed has only a few months to root before the hottest weather arrives.
Should I overseed or start the lawn over?
Overseed when most of the lawn is still decent grass. University of Minnesota Extension points to a full renovation when about 30 to 50 percent of the lawn is dead or very sparse, when weeds cover that much with too little grass left to fill in, or when the lawn feels soft and spongy from thatch thicker than ¾ inch.
Find out why the grass thinned before paying for seed. UMN starts a renovation with a soil test, and shade from growing trees, compaction, drought, insects and poor mowing all thin a lawn again if nothing changes. If the same patch fails every year, ask the contractor what will be different this time.
How is the seed put down, and how much?
Seed has to touch soil. UMD has the lawn mowed low, to about 2 to 2½ inches, the clippings raked off, and the surface roughened with a steel rake, core aerator, vertical mower or slit seeder. Its rates per 1,000 square feet: tall fescue 4 pounds, Kentucky bluegrass 1 to 1½ pounds, fine fescue 2½ to 3 pounds, spread in two directions at half the rate each.
A slit seeder cuts shallow grooves and drops seed straight into them; UMN says it takes skill to run and is generally a job for a professional. Core aeration followed by spread seed is the other route, and on compacted ground UMN recommends three to five aerator passes. A quote that only says "lawn treatment" should name the method and the passes.
What should an overseeding quote list?
The lawn area in square feet; the prep (mowing, raking, aeration or slit seeding, and how many passes); the seed by name and pounds; any starter fertilizer or lime; and the aftercare: who waters, how often, and whether a follow-up visit to reseed bare spots is included. Each on its own line, so you can compare it with a quote that bundles them.
UMN has the seed rolled lightly after spreading and the surface kept slightly damp until every variety comes up; Kentucky bluegrass alone takes as long as 2 to 3 weeks to come up. That means light watering, often enough that the surface never dries out, for weeks. If the watering falls to you, make sure someone is around to do it before you pay for the seed.
Frequently asked questions
Can I mow after overseeding?
Yes, and keep it short. UMN's advice is to keep the existing grass cut low for about a month, until the slowest seed is up, so light still reaches the seedlings, then raises the mower as the new grass catches up.
Can I overseed after using weed killer?
Check the label first. UMD says to follow any waiting period the label sets before grass seed goes down. UMN's renovation plan uses a non-selective herbicide that needs 5 to 14 days to work before seeding.
Will overseeding get rid of weeds?
Over time, a thicker lawn crowds weeds out, which is one reason UMD recommends overseeding every fall. Seed won't beat creeping weeds that are already established; UMD says to remove bermudagrass, ground ivy, mock strawberry and quackgrass before seeding.
Sources
- University of Minnesota Extension: Renovating a lawn · Checked
When to renovate, the overseeding window, aerifier passes, slit seeding, watering, germination and mowing new seed.
- University of Maryland Extension: Maintaining an established lawn · Checked
Autumn overseeding of cool-season lawns, seed rates per 1,000 square feet, preparation and weeds to remove first.
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