When planting grass seed it is not enough to properly prepare the soil, fertilize, choose a premium site specific grass seed, cover large seedbed areas to protect/retain moisture and routinely water. In addition to each of the critical steps mentioned above, grass seed must be planted when soil temperatures are expected to reach/remain at 50 degrees or above to successfully germinate.
Ideally, grass seed should be planted in late summer/early fall (late August thru September) for best results. Late summer/early fall is a great time of the year for planting grass seed (non-shade areas in particular) due to cooler air temperatures, lawns are coming out of dormancy, soil temperatures remain warm and there is very little chance of frost or prolonged freezing temperatures. In addition, rainfall becomes more routine and we experience less weed seed proliferation/competition for open exposed soil areas at this time.