Grass seed calculator

Water new grass seed two to four times a day during germination. Start with 5–10 minutes per area—enough to make the surface damp without puddles. After seedlings emerge, move toward once a day, then every two to three days with deeper watering as roots establish; adjust for rain, heat, wind, and soil.

Use a starter fertilizer if your soil needs phosphorus to support the new grass. For a new lawn, plan to fertilize at seeding; a soil test helps you choose the product. For overseeding, you may only need a regular lawn fertilizer once seedlings establish, often after the first mowing. Account for fertilizer already applied, and follow the bag’s rate and local phosphorus rules.

Use a thin layer of peat moss on small patches that dry quickly, and clean straw on large bare or sloped renovations. Add and blend topsoil or compost before seeding when construction, rocks, or compacted clay left a poor seedbed; do not bury the seed under a new layer. Keep any surface cover about 1/8 to 1/4 inch deep.

Do not use a standard pre-emergent before or just after seeding unless its label specifically allows that timing with your grass. It can stop grass seed from germinating; for other weed controls, wait until the new grass has been mowed as many times as the product label requires—often three or four.

Seed cool-season grasses in late summer to early fall and warm-season grasses in late spring to early summer. The soil should be warm enough for germination while the new grass still has several weeks of active growth before heat, frost, or dormancy.

Mow with a lightweight mower when the ground is firm and the grass is about one-third taller than the height you want. For a 3-inch cut, mow just before it reaches 4 inches.