Grass seed needs the correct soil and air temperature, as well as moisture content, to sprout. Planting it too early in the spring can result in less-than-ideal germination, because the seeds can die off or become unproductive.
Planting grass seed too early or too late can result in a lawn with gaps. Grass seeds need specific temperatures to germinate and enough time to grow strong roots before hot or cold weather sets in.
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It's too cold to plant grass seed if there is still the danger of frost in the spring or if the first frost of the late fall has arrived. Cool season grasses should be planted in early spring, typically in March. Wait until late spring to plant warm season grass seed -- May in most areas.
There may be problems if you try to plant grass too close to expected frosts. The seeds may rot from too much water and cold or die from frost.