September is the best month to reseed cool-season lawns such as tall fescue and Kentucky bluegrass. However, you can get by with an early to mid-October planting for tall fescue. October 15 is generally considered the last day for safely planting or overseeding a tall fescue lawn in the fall. If you do attempt a late seeding, take special care not to allow plants to dry out. Anything that slows growth will make it less likely that plants will mature enough to survive the winter.
Seedings done after the cut-off date can be successful, but the success rate goes down the later the planting date. Late plantings that fail are usually not killed by cold temperatures but rather desiccation. The freezing and thawing of soils heave poorly rooted grass plants out of the ground, which then dry and die. Keeping plants watered will help maximize root growth before freezing weather arrives. (Ward Upham)\
