We have southern grasses here, which fall into 3 main types:
- Bermuda (95% of Frisco has bermuda)
- St Augustine
Typically you overseed the southern grasses in the winter with rye. Most people do not do this, but you can do it for winter color. You would do this in the early fall and it dies out from the heat by summertime.
You can also overseed in the spring, but the grass seed has to be able to withstand the summer heat. The varieties that can do this are:
Bermuda - Only use this if you are seeding pasture or large bare areas. If your existing bermuda is thin from shade, don't seed bermuda into bermuda. Fix the shade issue or use a more shade lolerant grass type.
St. Augustine - This isnt available in seed, but can be sodded for better shade tolerance. This is a much wider blade of grass than bermuda, has different fertilizer requirements than bermuda, and IMO looks like crap mixed in with bermuda.
Zoysia - This can be seeded (sod is better though) into bermuda for better shade tolerance. Its only a little wider blade than bermuda and looks okay mixed together.
Tall Fescue - We are at the very southern limit on where Tall Fescue can survive. It has excellent shade tolerance, but it will thin in the summer heat. It also grows straight up, is a different shade of green and will really stand apart from bermuda and not look good mixed together.