The best time of year to plant grass seed is in the fall. Spring is good as well, but there are some problems associated with planting grass seed that will be explained in a moment.
People wonder why fall is the best time of the year to plant grass seed. It almost seems counterintuitive. Grass is a living thing that needs time to grow, so how can the end of the growing season be the best time of the year to plant? To some, that makes no sense.
Why Fall Is Best
Here's why fall is the best time. The temperatures are cooler than in the spring, making it easier to keep the grass seeds moist as they germinate. This is an ideal growing condition for seeds and seedlings. Cool, moist soil will allow your new grass seeds to grow firmly into the soil.
Since fall is at the end of the growing season, weeds that compete with seedlings are dead or have stopped growing. What's more, diseases are not nearly as prevalent in the fall, and insects are much less active. If all of these problems were present, you would need to contend with them by using herbicides and insect control chemicals. Neither one of these are conducive to growing new grass.
Finally, planting in the fall means that the seeds will have a chance to grow roots through the fall and then in the following spring, giving the new grass time to become strong and healthy before facing the heat of summer.
Spring is also a good time of year to plant. However, in order to control weeds, homeowners need to apply a pre-emergent herbicide. This means you can't grow grass seed too, so you'd have to pick one or the other. Also, spring is a much wetter season in general than fall. The increased amount of rain may wash the seeds away.