How to overseed a lawn
Thicken thin grass with new seed, step by step
What overseeding is
Overseeding means sowing grass seed into an existing lawn to fill thin areas and crowd out weeds. Cool-season lawns benefit from it every fall, and a very thin lawn may need two or three rounds.
Warm-season lawns, like zoysia and bermudagrass, are usually patched with plugs or sprigs instead. Bunch grasses like tall fescue can't spread sideways, so bare spots wider than about 4 inches (10 cm) need new seed.
When to do it
For cool-season grasses, late summer to early fall is best, from about mid-August into September or early October, depending on where you live. Spring sowing works, but it's harder, with more competition from weeds.
Step by step
Good contact between seed and soil is the secret.
- Mow low, to about 2–2.5 inches (5–6.5 cm), and rake up the clippings.
- Loosen the surface with a steel rake, or use a core aerator, vertical mower or slit seeder.
- Choose seed of the same type as your lawn, suited to its sun or shade.
- Spread half the seed in one direction and half across it, at the rate on the bag.
- Press the seed in with the back of a rake.
Water lightly and often
Keep the top inch of soil moist with light watering, usually twice a day and up to four times in hot, windy weather, for about three weeks. Seed sprouts in about 2 weeks; bluegrass takes longer. Then water less often but more deeply.
Start mowing when the new grass is about half again as tall as your usual mowing height.
Skip the crabgrass preventer
Most pre-emergent herbicides that stop crabgrass also stop grass seed from sprouting. Check the label for the waiting period, and hold off until the new grass has been mowed several times. Keep kids and pets off any treated lawn as the label directs.
A soil test tells you whether to lime or use a starter fertilizer. If you do, follow the label.
Related plant problems
Sources
- University of Maryland Extension: Maintaining an Established Lawn
- University of Maryland Extension: Starting a New Lawn
- NC State Extension: Extension Gardener Handbook, 9: Lawns
- Iowa State University Extension: Can I successfully sow grass seed after application of a preemergence herbicide?
General guidance, not a diagnosis. Written by PlantWiz in our own words from the sources above.