Every spring, people look at a thin lawn and buy seed. It is the most natural instinct in lawn care and, for cool-season grass in Tennessee, close to the least effective thing you can do. Spring seed germinates into a summer it is not old enough to survive, and most of it is gone by August.
The window that actually works opens in late August and closes in early October. Soil is still warm enough for fast germination, air temperatures are falling, and the young grass gets a long cool autumn plus an entire mild winter and spring to root before it ever faces real heat. Seed planted in September is nearly a year old by the time it meets its first July.
Do the prep before the seed goes down. Mow lower than usual for that one cut, clear the debris so seed reaches soil rather than sitting on thatch, and core aerate compacted areas, which describes almost every graded subdivision lot in Wilson County. Seed-to-soil contact is the entire game.
Fall is also the most important feeding of the year for fescue. The plant is putting its energy into roots rather than blades, and nitrogen applied now gets stored rather than burned off in a flush of top growth. If you only feed a fescue lawn once a year, do it in fall.
Then water lightly and often until germination, which is the opposite of normal watering advice. New seed needs the top half inch to stay damp for two to three weeks. Once it is up and has been mowed twice, switch to deep, infrequent watering and never look back.