Grass Seed Calculator

Seeding rates differ because seed size differs enormously: Kentucky bluegrass runs about 2–3 lb per 1,000 sq ft for a new lawn, perennial ryegrass 6–8, and tall fescue 6–10. The rates here are mid-range defaults — 5 lb per 1,000 sq ft on bare soil, 2.5 for overseeding — so always check the bag for the species you actually bought.

Starting from bare soil at 5 lb per 1,000 sq ft, that is 10 lb of seed, plus about 6 lb of starter fertilizer at 3 lb per 1,000. Overseeding the same lawn takes roughly half the seed, 5 lb, because the existing turf already holds the ground and you're only filling thin patches.

Cool-season grasses — bluegrass, fescue, ryegrass — establish best from late summer into early fall, when soil is warm, nights are cool, and annual weeds have stopped germinating. Spring seeding works but competes with crabgrass and runs into summer heat before roots are deep. Warm-season grasses like bermuda and zoysia are the opposite: seed them in late spring once soil holds above 65°F.

Doubling the rate produces a thick flush of seedlings that then compete with each other for light and water, thinning into weak, disease-prone turf. Germination depends on seed-to-soil contact and constant moisture, not density: rake seed lightly into the top quarter-inch, roll or tamp it, and keep the surface damp with short, frequent watering for two to three weeks.

Water less often but more deeply once seedlings are up, to push roots downward. Hold off mowing until the grass is about 3 inches tall, then cut no more than a third of the height with a sharp blade. Skip broadleaf weed killers until after the third or fourth mowing — most will damage or kill new seedlings.