Plan to plant grass seed in the Northeast in the fall, but know that you can also do it in early to midspring. According to the University of Missouri Extension, September is the best month because the seedlings have time to mature and grow strong roots to survive winter and thrive by the following spring.
Work on the planting area in August to prepare it. Use a rototiller to loosen the soil up to 6 inches deep, and apply herbicides if necessary to kill weeds. A soil test is helpful to tell you if there are any fertility deficiencies.
If you choose to grow grass seed in the Northeast in the spring, make sure to do it as soon as the danger of frost has ended. Broadcasting seed in late spring can result in a poor lawn because the grass may not have the chance to strengthen before the heat of summer arrives.