How long and how often to water after planting grass seed?
Long enough to moisten the entire surface of the seeded area, but not long enough that the water will run off in little rivulets. As often as necessary to prevent more than 50% of the surface from drying out. Follow these guidelines for about ten days, until the grass has sprouted and grown to an inch in height. Thereafter, water about an inch, once per week except in extremely hot, dry, windy weather, when you should water about 3/4 inch twice per week.
