Fall is considered the best time for planting or seeding cool season grasses because of several reasons:
Soil temperature: During the fall, the soil temperature is warm enough for the seeds to germinate, but not too hot for the seeds to dry out or overheat, which can affect their growth.
Moisture: Fall is often a time of increased rainfall, which can provide the moisture needed for the seeds to grow and establish roots.
Reduced competition: Planting in the fall means there will be less competition from weeds and other grasses for resources like sunlight, water, and nutrients, which can help the new grass establish itself more easily.
Forgiving weather: The mild fall weather is also beneficial for the new grass, as it provides the optimal temperature and light conditions for growth. In Spring, you have competition but you also have rising temperatures. If the newly seeded grass does not mature in time, it can get burned up.
Root growth: Cool season grasses tend to grow their roots more actively in the fall, which can help them establish a stronger and deeper root system, making them better equipped to handle the winter and spring weather.
For these reasons, planting or seeding cool season grasses in the fall can provide the best chance for a healthy and thriving lawn.