In Texas, the vast majority of the lawns are of the St. Augustine variety. There are some Bermuda-based lawns, however, along with some of Zoysia, and very few (if any) Centipede. Most people with St. Augustine yards have bits and pieces of Bermuda, but some are overwhelmed with it. The obvious answer to removing Bermuda is to kill it, till it and replace it with new sod. But that’s usually just for extreme cases where the Bermuda is absolutely solid. In most cases … where there is a mix of Bermuda and St. Augustine … cultural practices will help St. Augustine win the battle. Simply mowing properly is the answer nine in 10 times. If you mow as tall as your mower will allow, the St. Augustine will almost always crowd out the Bermuda. Conversely, if you want to accelerate the Bermuda, mow shorter and more often — then the Bermuda will win.
The reason is Bermuda can’t grow in shade — taller St. Augustine will shade the slower growing Bermuda. Yes, you still have to mow once a week, but if your neighbors don’t come up to your level, it is going to look like you don’t mow at all. However, I promise your lawn will be a richer green with a thicker texture than your shorter-cutting-neighbors. I call it the “Bring Your Neighbor Up to Your Level” debate. And there is an added benefit to growing taller-than-normal St. Augustine. You won’t need to irrigate as frequently. First, because tall grass supports deeper roots which have more water available to them far down in the soil. Grass blades have microscopic pores (stomata) to transpire carbon dioxide (CO2), oxygen and water vapor. The stomata open in the morning and close when they get their fill of CO2. Since taller grass has more stomata exposed, it more readily collects CO2 released by soil microbes. And, as CO2 is heavier than air and tends to remain close to the ground, it’s harder for wind to blow it away in taller grass. Therefore, tall grass gets more CO2 because it has more stomata and because the amount of CO2 is denser near the stomata. And, as a consequence, the stomata close off earlier in the day shutting off the transpiration of water vapor from the plant and allowing the plant (and soil) to retain water better.