Grass seed does best when it is sowed around temperature extremes. Dispersing the seed when it is too hot or too cold will cause the seed to die and slow down root development and spread.
Grass seed can be sowed in spring or late summer to early fall. Spring planting (April is ideal) gives the young grass time to develop roots before the heat sets in. If you're eyeing the fall, cool-season grasses do best when planted between August 15 and September 15.
Plant cool-season grass when the soil temperature is between 10 and 18.3 degrees Celsius. Warm-season grass seed grows best in soil temperatures of 18.3 to 21.1C. If you live in Southern states, warm-season grasses should not be planted later than 60 days before the first frost. If you live in Northern states, plant no later than 90 days before the first frost.
You can lay grass seed in the late fall if needed. It may not have time to germinate, however. The seed can stay dormant all winter and sprout when spring arrives. There is a risk -- the seed may be washed away during winter.