September 22nd is the first day of fall. Many people end up thinking about the entire month of September as fall but in fact fall does not offically start until near the end of the month. Signs of fall that will tell you that it is near or has arrived are often cooler weather; especially nights and early mornings, the changing of leaves to colors like red, brown and orange, and harvest season.
Fall is a sure sign that crops that have been gowing all summer will be harvested. There are often celebrations and festivals centered around harvesting time.