You should keep the seedbed evenly moist until most or all of the seed has germinated, which can take 10-21 days (depending on the type of seed). Until germination, you should water two to three times per day for short periods of time. Once germinated, the grass will require less water and you can water just once per day. When the grass is tall enough to mow (three inches), you can reduce watering to two or three times per week for 15-20-minute periods.