On a typical bag of fertilizer, there are 3 numbers listed on the bag. The numbers stand for N-P-K. N is NITROGEN content of the fertilizer. P is for PHOSPHORUS. K is for POTASSIUM (sometimes known as potash). If you are thinking of putting any type of soil amendment on your lawn after about the end of August to around September 1st (think: when kids are going back to school), make sure it has a "0" in the N spot on the fertilizer bag. Let me say it again. Do not apply a fertilizer to your lawn after around September 1st that contains Nitrogen. Once the kids are starting to go back to school, no nitrogen. Do not put nitrogen on your warmseason turfgrass lawn in the fall. I don't know how many other ways I can phrase it to get the point across.
No matter how tempting it might be for you to pick up a bag and spread it out because you think you need to "feed" your lawn to get it through the winter.... don't do it! Your warmseason lawn could be injured by applying a nitrogen-containing fertilizer in the fall. In short, nitrogen applied during the fall could promote new growth to the green part of your grass. This tender new growth will not be "hardened" off, and when a frost comes, it will get damaged. Furthermore, nitrogen applied in the fall could actually feed any cool season WEEDS that might emerge. Now, we surely don't want that to happen!
If you are just bursting at the seams to put SOMETHING out on your lawn for the fall, choose a no-nitrogen, light application of potassium (potash) for your warmseason lawn. If your lawn has been regularly fertilized throughout the summer with a "normal" 16-4-8 fertilizer, though, there is a chance that a fall application of potassium just frankly won't do much good. Save your money. Don't fertilize right now. There are some good management practices that, if put in place at the right time, could promote better cold tolerance of your warmseason lawn through the winter. But that's another blog post.