Hydroseeding is a process by which seed, mulch, plant fiber, water and fertilizer are combined into a slurry and then sprayed across soil. This allows a quick and easy method to plant grass seed across large surfaces. The mixture binds to the soil and creates a protective top-coat in which moisture is retained. This protects the seed until such time as they germinate. But the process isn't entirely foolproof.
Before the lawn is sprayed down with seed, till it thoroughly. Rake up any plant or weed roots that you can find and dispose of them. After that, smooth out the surface so there will be no significant humps and bumps that make the grass cover look uneven once it's grown in. Use a lawn roller to flatten the soil out and get rid of any air pockets, then leave it for a few weeks. Try though you might, weed seeds will have been left in your soil, so take the time to let them sprout and then pull them before hydroseeding.
Pick a Time to Seed
The seeds won't grow unless their placed at just the right time of year. There's no point hydroseeding your lawn and then waiting for six months; most of the seed will have died anyway. Generally speaking, the best time of year to seed your lawn is in early autumn, just as the summer heat is beginning to die. This way the soil is still warm enough for germination but keeping the seeds hydrated isn't such a worry as it would be in high summer. Spring is also a poor choice because the soil will still be cold from winter and the grass might have to compete with weeds. Again, this is just a general tip as there are some regions where the winters are so cold that seedlings are frozen before they've a chance to mature.
For the first few weeks after your lawn has been hydroseeded, water it between 2 and 3 times a day. The outermost layer or topcoat of the hydroseed slurry helps to protect, warm, and germinate the seeds. It is very porous seeing as it's mostly ground plant matter, but it can harden if not kept wet. Then the seeds would be unable to grow and break through this layer. Never water the slurry so much that puddles develop; too much water can break up the mixture.
Once the slurry is down, only concern yourself with watering it. Don't fertilize it; the fertilizer is already in the mixture. Let it grow out long and thick before you mow it for the first time; the root system will be more established and better able to handle the shock. Finally, don't walk on it. The topcoat may be hardened or the grass may already have sprouted, but the coating still protects the grass seed from air, wind, and cold. Putting weight on the coating could either break it open or compress the seed and inhibit their growth.