Step 1: Irrigate the soil daily, at least twice a day, but possibly more. Try not to let soil completely dry out. If your seed is planted in bare soil, do not soak or flood your lawn. When watering a new lawn, use just enough water to keep the soil moist at seed depth. Standing water or prolonged heavy rain could ruin some of the seed or possibly wash the seed away.
If over seeding a lawn where you have established grass, be sure to keep the seed moist by watering lightly twice a day. Occasional deep watering is okay to maintain grass health. The existing grass will help keep the seed in place, shade the soil, and slow evaporation.
Step 2: Once the seed has sprouted continue watering lightly, but allow the soil to dry slightly before watering again. At the seedling stage, it is even more critical not to repeatedly saturate the soil. Persistently wet soil can lead to serious root diseases, such as pythium blight, that can kill the roots. Very humid weather often has greater disease problems than dry weather.
Step 3: When the grass is a couple inches tall cut back on water to once every two to thee days, depending on the temperature. Tiny seedlings can still suffer if the temperature spikes and the soil dries out. Soil dries faster in hot, arid environments than humid environments than humid environments.
Step 4: Once the grass reaches the cutting height for your particular grass type begin watering deeply, but less often, so the soil is wet to a depth of four inches. After watering, don’t water again until the grass begins to show signs of stress. This trains the roots to grow deeper into the soil to reach available water and nutrients.
Additional Information & Tips: Grasses are “monocots”, meaning they emerge from the soil as a single blade. This single blade develops into a larger plant, but it will take time. Don’t expect to have thick lawn in a few weeks. It can take years to get a thick, healthy turf when starting with seed on bare soil.