With this mild winter we had, you should've started a month ago.
There's also this guy to follow, but he goes nuts when people use weed & feed because of the Atrazine ingredient many contain.
Atrazine slowly kills plants and trees. He focuses on SE Texas.
http://www.randylemmon.com/tip_sheets.htmlI still use weed & feed with Atrazine because I want the weeds dead and don't have the patience to do all the things he says.