Site preparation is important whether you're sowing grass seed or hydro-seeding. Remove debris, loosen up the soil with a rototiller and rake it until it's level. A starter fertilizer will help the seed germinate faster.
Mechanical and hand spreaders are available to broadcast grass seed. Fill the machine with half the seed and make one pass over the yard, then move in a different direction, dispersing the other half of the seed. Keep the seed moist until you see grass sprouting. It can take anywhere from 5 to 30 days, depending on the type of seed.
Hydro-seeding contractors are the best bet when hydro-seeding because they have the equipment to spray the grass seed over the yard, along with a starter fertilizer that is high in phosphorus. Make sure you keep the seeds moist until they root, which takes about two weeks.