Overseeding Calculator
Find out how much grass seed to overseed and exactly when. Enter your ZIP, grass type, and lawn size for pounds of seed, bag counts, and your best overseeding window with a countdown.
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2 minutesOverseeding rates, timing, and how-to
Overseeding uses roughly half the seed of a new lawn, because you are thickening living turf, not starting from bare soil. Rates below are pounds of uncoated seed per 1,000 sq ft; coated seed needs about 1.5 times as much.
| Grass type | Overseed rate | Best season | Notes |
|---|---|---|---|
| Tall Fescue | 3–4 lbs / 1,000 sq ft | Fall (Aug–Oct) | The classic overseeding grass; germinates in 7–14 days |
| Kentucky Bluegrass | 1–1.5 lbs / 1,000 sq ft | Fall (Aug–Sep) | Tiny seed, slow to establish (21–30 days); be patient |
| Perennial Ryegrass | 3–4 lbs / 1,000 sq ft | Fall or spring | Fastest germination of any lawn grass (5–7 days) |
| Fine Fescue | 2–3 lbs / 1,000 sq ft | Fall (Aug–Sep) | Best pick for shady lawns |
| Bermudagrass | 0.5–1 lbs / 1,000 sq ft | Late spring (May–Jun) | Needs soil 65–70°F; hulled seed sprouts faster |
| Zoysiagrass | 0.5–1 lbs / 1,000 sq ft | Late spring (May–Jun) | Slow from seed; plugs often beat seed for repair |
| Centipede | 0.25–0.5 lbs / 1,000 sq ft | Late spring (May–Jun) | Very low rate; do not over-apply |
| St. Augustinegrass | Plugs / sod only | Plugs: May–Jul | No viable seed sold; use plugs, sprigs, or sod |
Patchier lawns use the high end of each range. Enter your grass, ZIP, and lawn size in the calculator for exact pounds and bag counts.
The right rate and prep depend on how much living grass you have left.
If more than half your lawn is living grass, overseed. You will thicken what is there at about half the seed of a new lawn, with no tilling, and the lawn stays usable: aerate, spread, and water lightly for two to three weeks. If you are looking at mostly bare dirt, that is a reseeding project instead, with full seed rates, real soil prep, starter fertilizer, and six to eight weeks before the lawn takes traffic. The seeding calculator handles that case, including the 'is it too late this year?' verdict.
Seed-to-soil contact and steady moisture are what separate a thick result from wasted seed.
- Core-aerate first. Seed-to-soil contact through thatch roughly doubles germination. Aerate the same day you seed.
- Mow low (about 2 inches) and bag the clippings so seed can reach the soil surface.
- Spread at your calculated rate with a broadcast or drop spreader, ideally in two passes at half rate for even coverage.
- Apply a starter fertilizer at seeding for the planting-time phosphorus boost, and skip weed control for four weeks on either side.
- Water lightly two to three times a day for two to three weeks, until the new grass has been mowed once.
Bermuda, zoysia, centipede, and St. Augustine play by different rules than cool-season turf.
Warm-season grasses overseed in late spring once soil reaches 65 to 70°F, not in fall. In southern regions, many homeowners overseed dormant Bermuda or zoysia with perennial ryegrass in October to November (5 to 10 lbs per 1,000 sq ft) for green color all winter; the rye dies off when summer heat returns. St. Augustine is the exception: there is no viable seed sold, so thin areas are filled with plugs, sprigs, or sod planted from late spring through mid-summer.
How much grass seed do I need to overseed?
Overseeding uses roughly half the seed of a new lawn: about 3 to 4 lbs per 1,000 sq ft for tall fescue and perennial rye, 1 to 1.5 lbs for Kentucky bluegrass, and under 1 lb for warm-season grasses like Bermuda. Patchier lawns use the high end. Enter your grass, ZIP, and lawn size above and the calculator scales it to exact pounds and bag counts.
When is the best time to overseed?
For cool-season lawns (fescue, bluegrass, rye), early fall is the best window: warm soil, cooling air, and fading weed pressure. Spring is a workable backup. Warm-season lawns (Bermuda, zoysia) overseed in late spring once soil hits 65 to 70°F. The calculator gives your exact window by ZIP with a countdown.
Can you overseed St. Augustine grass?
Not from a bag. Commercially viable St. Augustine seed is not sold, so thin St. Augustine is repaired with plugs, sprigs, or sod, planted late spring through mid-summer. Pick St. Augustine above and the calculator switches to a plug-tray plan instead of a seed quantity.
Should I overseed Bermuda with ryegrass for winter?
In southern regions, yes, if you want green grass through winter: perennial ryegrass at 5 to 10 lbs per 1,000 sq ft in October to November. It grows all winter and dies off when summer heat returns. Skip it if your Bermuda is stressed, since the rye competes with spring green-up.
Do I need to aerate before overseeding?
It is the single best prep step. Core aeration opens seed-to-soil contact through thatch, and germination roughly doubles when seed lands in the holes. Aerate the same day you seed, right before spreading, and check the aeration calculator for your timing.
Should I use coated or uncoated seed?
Coated seed holds moisture better for beginners, but roughly a third of the bag's weight is coating, so you need about 1.5 times the pounds to put down the same amount of live seed. Flip the coated toggle in the calculator and the math adjusts automatically.
How soon can I mow and fertilize after overseeding?
Wait until the new grass reaches mowing height (about 3 inches) before the first cut, usually 3 to 4 weeks. Use a starter fertilizer at seeding for the phosphorus boost, and hold off on any weed control for at least 4 weeks on either side of seeding.