Round #4 (late August to mid-September)
Autumn is the most important time of year for your lawn’s development. There is a natural change of focus in the growth cycle, namely less top growth and more root growth. So, the autumn prep lawn fertilization maximizes this natural tendency to develop the root system in your lawn. It is important though, to also make sure your lawn gets adequate water during this season, or it will be like being on the right road with no gas. So many times I have seen September and October looking as dry as summer. Your lawn should NOT turn brown in the fall. Keep it watered!
Check out this article about autumn lawn care.