When to apply fall lawn fertilizer in Dallas, DFW, and North Texas is not the most important question to be asking. What type of fertilizer, weed control, and preemergent to apply in the fall in the north Texas area is the most critical question.
First Question: When to put down and apply preemergent in North Texas to stop annual bluegrass?
Answer: You need to do it twice per year. Please go to this old blog post to get more details: https://turfgrassscience.com/when-is-the-best-time-apply-pre-emergent-in-dallas-north-texas/
Second Question: What is the best lawn fertilizer winterizer to use for grass in the fall?
General Answer: Best lawn winterizer is just a marketing term. "Winterizer" really just stands for something high in potassium. And most lawns need something high in potassium in the winter. K stands for Potassium. And it is the last number on the fertilizer bag. Example: 8-4-24. The 24 is the percentage of Potassium in the bag.
Better Answer: fall is the best time to do soil testing in Dallas. Then, take the results of the soil test and apply whatever is deficient in your yard, + some Potassium. In North Texas black clay, there is a high chance your yard is going to be deficient in phosphorous (the middle digits) and along with having a high PH. And since it takes nearly six months to significantly lower pH in lawn soil, then doing it now gets you ready for Spring. Read more about it here: How much sulfur to lower PH in lawn soil.
Phosphorous, however, can be absorbed into the soil pretty quickly. Please go to this blog post to read more about it: How to add phosphorous to the soil quickly.
Third question: When to fertilize lawn in fall in Dallas, north Texas?
If you are not overseeding with perennial ryegrass, or "winter rye," as Texans like to call it, then this will be based on the zone you live in. In North Texas, we are in zones 7b to 8A (unless you are in the panhandle, which is not considered North Texas). And since "winterizer" is not a time-sensitive application for lawns, then applying the lawn fertilizer service anytime from October 1 to October 20th is going to be sufficient.
Lastly, if you have big bare spots from the near-record heat this summer or bare spots around trees, fall is the best time to trim trees, do a soil test, and start the disease testing process. To read about the various types of lawn fungus in North Texas and disease testing options, please click here: Lawn Fungus Disease Testing in North Texas.