Late summer/early fall planting of grass is considered better than spring planting. Fall planting gives new grass two complete growing seasons before it goes through the hot, dry summer of the following year.
Northern Indiana is in planting zone 5 and is a little cooler than the southern third of the state. August 15 through September 15 is the best time for grass seed planting for those in the northern part of the state..
Southern Indiana is zone 6. September 1 through September 30 is the best window for planting in this area, according to Indiana's Purdue University Turfgrass Program.
Planting as early as possible within those dates is optimum Every day missed may mean two fewer days for the grass to mature.