The single most important requirement for successful germination of your seeding is adequate moisture. Without proper moisture, the seed will not germinate and will eventually die. Keeping the seed damp either by rainfall or irrigation is required to encourage proper seed development.
The first watering can be done right away. It should be a good soaking to moisten the soil to a minimum depth of three inches. This usually requires an inch of actual water. Water gently, being careful not to apply the water with such force that it washes away the soil or dislodges the seed.
After the initial watering, irrigate the seeded areas lightly and frequently, enough to keep the seed and soil surface moist. The frequency of these sprinklings is dependent on the weather conditions and the amount of thatch protecting the new seed. Lawns with little thatch protection or lawns that are subjected to warm temperatures may need to be watered as frequently as 2-3 times a day. Lawns with thatch or lawns subjected to cooler temperatures will need less frequent irrigation. Check your soil daily to determine how often you need to water to keep the soil surface damp.
Once the grass begins to establish and mature, the frequency of your sprinklings can be lengthened, and the amount of water applied at one time increased.