Your best source of information about this would be
Texas A & M Cooperative Extension Service. The link below is one article from them.

Here is a link that might be useful: Growing St. Augustine grass

Hi Woodlands
We've been in Houston since '74, and I have gotten more bad advice than good concerning St Augustine grass. I think mine is good, but I DO know that the A&M advice is a little dated regarding organic methods.
So here's my two cents worth
We're in the middle of a multi year drought, which caused a lot of lawn soils to go sterile. Get some good quality compost and topdress the lawn, about 1/3 inch is enough. Add some minerals, I use greensand every 2 or 3 years.
Don't sweat the weeds, they will get crowded out, but BOAP the big ones if they bother you.
Cut 3.5 to 4 inches high, only water weekly at most but water deeply. Daily watering WILL kill your lawn, causing shallow roots that won't take summer stress.
Apply Actinovate after the compost and greensand with a soaking spray to get to the roots under the compost.
Good Luck