Growing a new lawn from seed isn't rocket science, but it does require extra care and attention to result in lush grass. As they grow and their roots burrow into the soil, new grass seeds require lots of water to become established and dehydration may result in a sickly, unsightly lawn. You will also need to protect the seeds from hungry birds and foot traffic.
Proper watering should begin just before you seed a lawn, creating moist, inviting growing conditions. A few days before spreading the seeds, water the area to be planted to a depth of 6 to 8 inches, recommends University of California Agriculture and Natural Resources. When you do this, add a little a compost to the soil to make it richer and more hospitable. Allow the area to dry completely before adding seeds.
Just After Seeding
After sowing the grass seeds, they will need frequent watering on an as-needed basis. Keep the top 2 inches of soil moist, but not sopping wet. Water whenever the soil is becoming dry. Feel the soil to see if it's moist or dry. If the soil gets too dry, the germination process will stop. When watering, do not water so much that it pools on the soil's surface.
As the grass seeds germinate and develop roots, continue regular watering to help them become well established. Over the next month, check the seed bed regularly and water it lightly whenever it is dry, much like in the period right after seeding. During dry spells, check the new lawn more often, as it will need more water. Pay particular attention to shady patches of the lawn, as they need watering less often than sun-soaked areas.
When the grass seeds are established, their water needs lessen. Generally, give the lawn about 1 inch of water a week, delivered in one or two sessions. Doing so helps the roots of the grass grow deep into the ground and makes the lawn more tolerant of drought. Try to water in the early morning to avoid excessive evaporation, but avoid watering at night, as it will sit too long, increasing the risk of fungal disease.
University of California Agriculture and Natural Resources: Irrigating New Lawns
University of Minnesota Extension: Seeding and Sodding Home Lawns
State of Minnesota: Water Efficient Lawn Watering Practices
Garden Counselor Lawn Care: Watering New Grass Seed
Popular Mechanics: The Smarter Way to Water Your Lawn