Quick answer
Overseeding with ryegrass in fall gives you a green lawn through winter, but it means mowing in winter and can slow Bermuda's spring green-up. It's a looks-versus-upkeep decision.
Pros
- Green color all winter
- Helps cover thin areas visually
- Reduces winter weeds by filling space
Cons
- Requires watering and mowing in winter
- Competes with Bermuda during spring transition
- Can't use most fall pre-emergents
Timing
If you do it, seed in early to mid fall as Bermuda slows down, and water lightly until the rye establishes.