Killing Weeds in St. Augustine Grass

Section through soil with a dandelion weed and tap root against a white background

Even with the most robust grass types, weeds can still become an issue for any homeowner who is trying to maintain a healthy, attractive lawn. Each type of ground cover has its own strengths and vulnerabilities, when it comes to weeds.

St. Augustine grass, fortunately, is a robust grower with thick thatch and relative dense carpeting. However, even the most diligent lawn care enthusiasts may still face the task of addressing invasive species from time to time.

The best thing you can do to prevent invasive plants in your yard, no matter what type of grass you’ve got, is simply to keep it healthy. Beyond that, it’s a matter of knowing which herbicides will work well with your lawn.

Let’s take a look at some helpful tips to address and prevent weeds in St. Augustine grass.

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Preventing Weeds

  • Don’t mow too low. Just like other common North Texas grasses with a thick thatch, you want to keep that undergrowth in place with St. Augustine. It blocks seeds from taking root in your topsoil, thus creating a natural form of weed prevention.Keep your grass 1-1.5 inches high, to avoid cutting into the thatch.Additionally, St. Augustine’s dense blades provide a secondary deterrent. A nice, rich top layer of hearty blades makes it that much more difficult for opportunistic seeds to reach your soil and invade your lawn. For sloped landscapes, check out Best Lawn Mowers For Hills.
  • Provide adequate irrigation. St. Augustine grass, as resilient as it is, doesn’t tolerate drought as well as some other common ground covers. Check your local watering schedules, and do your best to provide at least an inch of watering per week.This measure keeps your grass plump, promoting stringent, even growth across your lawn. A weak bed of grass is more vulnerable to weeds. So water it well, and keep an eye on shady spots to be sure they’re thriving.
  • Fertilize appropriately. While the most popular North Texas lawn covers do well in this region, they are not necessarily native to this area. This means you need to be mindful of optimal soil pH to be sure your grass has adequate nutrients year-round.Once again, a strong lawn is a weed-resistant lawn. Do your research, check with your local lawn care experts, and read the labels when you’re buying fertilizer. This will ensure you’re nourishing your lawn with the proper additives at the appropriate times.

Removing Weeds

  • Read your labels: know your grass. St. Augustine grass is a bit more sensitive than other types when it comes to weed killers. You often only need to use about 1/2 the recommended amount (per the instructions on the bag).If you aren’t sure which ratio of nutrients your grass needs, or how much you should dispense in a given application, please reach out to a professional for guidance. We want to help you keep your lawn beautiful!
  • When to use a pre-emergent herbicide: These are the weed killers that work at the soil level, killing weeds before they get a chance to sprout. With St. Augustine grass, it’s safest to use these products when the daily high temperature is not exceeding 65-70*.
  • When to use post-emergent herbicide: These are the weed killers that attack plants after they’ve already sprouted. This method is most effective during active growth- typically from mid-May to early June.If you’ve effectively applied a pre-emergent weed killer earlier in the year, you should only need to utilize post-emergent products as a spot-treatment for errant weeds that crop up later in the spring and summer.
  • Wait to mow! During the summertime, when it’s best to use a post-emergent product, you want to wait a day between application and mowing your lawn. Post-emergent herbicides work by soaking into the weeds’ foliage, so you want give that process a chance to work the way it’s intended to.Chopping off your weeds with the mower directly after applying a weed-killer simply removes the treatment you’ve just applied. Wait a day or two, and let the chemicals do their job.
  • Autumn applications: For St. Augustine grass, if you want to proactively apply an additional round of herbicide, September is ideal. Of course, this depends on the climate of your immediate region, but you want to aim for a time of year when the daily high temperatures are beginning to drop below 85-90*.This measure ensure that you will avoid chemical burns from the mix of extreme heat and chemical application to your lawn. Waiting until Autumn weather sets in will allow you to avoid weed propagation while protecting the health of your grass.
  • Hand-pulling is always an option. Yes, it’s time-consuming. But using appropriate gardening tools to pull weeds up by the roots is a trustworthy method. If you’ve got a mild infestation of dandelions, clover, or some other weed that tends to crop up in small clumps, digging them out by the roots is a sure-fire way of stopping the problem before it spreads.


St. Augustine grass is popular for its beauty, resilience, and density here in the North Texas region. Keeping healthy is the first step to avoiding invasive species. However, if you are facing a weed problem, you can follow the steps we’ve outlined to address the issue quickly and safely.

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