Overseeding a lawn: rates, timing and steps

Quick answer

For cool-season lawns, overseed in late summer to early fall, roughly mid-August to late September in much of the North. Typical overseeding rates per 1,000 sq ft are about 6 to 8 lb for tall fescue, 4 to 6 lb for perennial ryegrass, and 1 to 2 lb for Kentucky bluegrass. Mow low, rake or aerate so seed reaches soil, spread the seed, rake it in lightly, and keep the top inch of soil moist until the new grass is up.

Overseeding rates by grass type

Overseeding rates are roughly half of the rate for seeding bare ground, because the existing lawn already covers part of the area. Always check the seed bag, since rates vary by blend.

Bluegrass seeds are tiny, which is why the rate is so low. Tall fescue seeds are large, so more pounds are needed for the same seed count. The grass seed calculator turns your lawn size and grass type into pounds and bags.

When to overseed

Cool-season lawns

Late summer to early fall is best. The soil is still warm, which speeds germination, while cooler air and fall rain help seedlings grow, and fewer weeds sprout. Aim to seed at least 45 days before the first expected fall frost so seedlings can establish. Early spring is a second choice; summer heat and crabgrass compete with young grass, and many crabgrass preventers also stop grass seed from sprouting.

Warm-season lawns

Bermuda and similar grasses are seeded in late spring to early summer, once soil temperatures stay above about 65 degrees F. Many warm-season lawns (St. Augustine, most zoysia) spread by runners and are repaired with sod or plugs instead of seed. In the South, some people overseed dormant Bermuda with perennial ryegrass in fall for winter color; that is a temporary cover, not a permanent fix.

Step by step

1. Check for herbicides. Do not overseed within the waiting period on the label of any pre-emergent or weed killer you have used, often several weeks to a few months.
2. Mow low. Cut the lawn shorter than normal, around 2 inches for cool-season grass, and bag the clippings. This lets seed reach the soil and light reach seedlings.
3. Open the soil. Core aerate, use a slit seeder or dethatch, or for small areas rake hard with a garden rake. Seed sitting on thatch rarely survives.
4. Fix bare spots. Loosen the soil in bare patches and add a thin layer of compost or topsoil.
5. Spread the seed. Use a broadcast or drop spreader. Set it to half the rate and make two passes at right angles for even coverage.
6. Work it in. Lightly rake so seed falls into holes and contacts soil. A thin topdressing of about 1/4 inch of compost helps hold moisture.
7. Fertilize. A starter fertilizer is commonly applied at seeding if your soil test shows phosphorus is low. Check local rules; some states restrict phosphorus on lawns.
8. Water. Keep the top inch moist with light watering once or twice a day until seedlings appear. Then water less often and more deeply.
9. Mow when ready. Resume mowing when new grass reaches about 3 to 4 inches, and keep mower height at the normal setting.

How much seed for your lawn

Pounds of seed = lawn area / 1,000 x rate. Example: a 5,000 sq ft tall fescue lawn at 7 lb per 1,000 sq ft needs 5 x 7 = 35 lb. A Kentucky bluegrass lawn the same size at 1.5 lb needs about 7.5 lb.

Mistakes to avoid

• Seeding too heavy. Extra seed makes crowded seedlings that compete and are more prone to disease.
• No soil contact. Spreading seed over tall grass or thick thatch wastes most of it.
• Letting it dry out. Once a seed starts to sprout, a single dry afternoon can kill it.
• Cheap seed. Check the label for weed seed and "other crop" content and pick named, improved varieties.
• Heavy leaf cover. In fall, rake or mulch-mow leaves so they do not smother seedlings.

Plan your next feeding with the fertilizer calculator, which converts a nitrogen target into pounds of product.