Bermuda Grass In St Augustine Lawn – How To Eradicate Invaders
Do you dream of a thick, emerald-green carpet of St. Augustine grass, only to find wiry, thin stems creeping through the blades? It is incredibly frustrating to see a uniform lawn interrupted by a patchy, aggressive invader. You are not alone in this struggle, as many homeowners face this exact turf war every single spring.
The good news is that you can reclaim your yard without starting from scratch. I promise to walk you through the exact steps to identify, suppress, and eventually remove these unwanted guests. By the end of this guide, you will have a clear, actionable plan to restore the lush beauty of your landscape.
In the following sections, we will explore why dealing with bermuda grass in st augustine lawn is a common challenge and how to use mowing heights to your advantage. We will also dive into the specific herbicides that are safe for your turf but tough on invaders. Let’s get your lawn back on track together!
What's On the Page
- 1 Why bermuda grass in st augustine lawn is so difficult to control
- 2 Identifying the Intruder: Spotting the Difference
- 3 The Cultural Approach: Smothering with Height
- 4 Chemical Warfare: Selective Herbicides for Success
- 5 Mechanical Removal and Patch Repair
- 6 Long-Term Prevention and Maintenance
- 7 Frequently Asked Questions About Bermuda Grass in St. Augustine Lawn
- 8 Conclusion: Reclaiming Your Green Sanctuary
Why bermuda grass in st augustine lawn is so difficult to control
To defeat an enemy, you must first understand how it thinks—or in this case, how it grows. Bermuda grass is one of the most resilient plants in the world. It is often referred to as “the devil’s grass” by frustrated gardeners for a very good reason.
Unlike St. Augustine, which primarily spreads through above-ground runners called stolons, Bermuda grass is a dual-threat athlete. It spreads via stolons on the surface and through underground stems called rhizomes. These rhizomes can dive deep into the soil, making the plant nearly impossible to pull out by hand.
When you notice bermuda grass in st augustine lawn, you are seeing a plant that thrives on neglect and high heat. While your St. Augustine might struggle during a mid-summer drought, the Bermuda is just getting started. It grows faster, requires less water, and can quickly outpace your desired turf.
Another challenge is the “common” variety of Bermuda grass. It produces thousands of tiny seeds that can stay dormant in your soil for years. One heavy rain or a bit of soil disturbance can trigger a fresh breakout. This is why a one-time treatment rarely solves the problem for good.
The Biological Mismatch
St. Augustine is a shade-tolerant, salt-tolerant grass that prefers to be kept tall. Bermuda, on the other hand, is a sun-worshipper that thrives when mowed short. These two grasses have completely different growth habits, which is actually the key to controlling them.
If you treat your lawn like a golf course (mowing it very short), you are essentially inviting the Bermuda to take over. You are creating the perfect environment for the invader while stressing out your St. Augustine. Understanding this balance is the first step toward a successful restoration project.
Identifying the Intruder: Spotting the Difference
Before you reach for any chemicals, you must be 100% sure you are dealing with Bermuda grass. I have seen many beginners accidentally kill their entire lawn because they misidentified a weed. St. Augustine and Bermuda look very different once you know what to look for.
St. Augustine grass has wide, coarse blades with a rounded or “boat-shaped” tip. The color is typically a deep, dark green. Its runners are thick and fleshy, often looking like green snakes crawling across the soil surface.
Bermuda grass is much finer. The blades are narrow and come to a sharp, pointed tip. The stems are thin, wiry, and much tougher to break. If you see a patch that looks like a fine-textured mat compared to the rest of your lawn, you’ve found your target.
Check the Ligule
If you want to feel like a true pro, look at the ligule—the small area where the leaf blade meets the stem. In Bermuda grass, the ligule consists of a fringe of white hairs. St. Augustine has a much shorter, inconspicuous ligule.
Another giveaway is the seed head. Bermuda grass produces a distinct seed head that looks like a small bird’s foot or a miniature windmill. St. Augustine rarely produces visible seed heads in a well-maintained lawn, and when it does, they look like thick, spiked stalks.
The Cultural Approach: Smothering with Height
The most effective “secret weapon” in your arsenal isn’t a chemical—it’s your lawnmower. Because these two grasses have opposite preferences for height, you can use mowing frequency and height to tip the scales in favor of your St. Augustine.
St. Augustine grass thrives when it is kept between 3.5 and 4 inches tall. At this height, the broad blades create a dense canopy. This canopy acts as a natural umbrella, blocking sunlight from reaching the lower-growing Bermuda grass hiding underneath.
Bermuda grass is an obligate heliophyte, which is a fancy way of saying it absolutely must have direct sunlight to survive. By keeping your lawn tall, you are effectively “shading out” the invader. Over time, the Bermuda will weaken because it cannot photosynthesize efficiently.
Watering and Fertilization Tactics
Your watering schedule also plays a role. Bermuda grass is incredibly drought-tolerant. If you water lightly and frequently, you are encouraging shallow root growth that benefits the invader. Instead, water deeply and infrequently.
Aim for about one inch of water per week, delivered in one or two long sessions. This encourages the St. Augustine roots to dive deep into the soil. A healthy, deep-rooted St. Augustine lawn is much better at competing for nutrients and space.
Be careful with nitrogen. High doses of nitrogen in the peak of summer can cause a growth spurt in Bermuda grass. I recommend using a slow-release fertilizer. This provides a steady stream of nutrients to your St. Augustine without giving the Bermuda a “sugar high” of growth.
Chemical Warfare: Selective Herbicides for Success
Sometimes, cultural practices aren’t enough, and you need to bring in the big guns. However, preventing the return of bermuda grass in st augustine lawn requires extreme caution. Most “weed killers” that kill Bermuda will also kill St. Augustine.
The gold standard for this specific problem has historically been Atrazine. Atrazine is a selective herbicide that is safe for St. Augustine (when applied according to the label) but can suppress Bermuda grass and kill many broadleaf weeds. It works by inhibiting photosynthesis.
Another option that professionals use is Ethofumesate (often sold under the brand name Prograss). This is a more specialized chemical. It is highly effective at suppressing Bermuda grass in St. Augustine, but it is often expensive and can be tricky to find at local big-box stores.
Safety and Timing Precautions
Never apply herbicides when the temperature is above 85-90 degrees Fahrenheit. Doing so can cause “phytotoxicity,” which is just a professional term for burning your grass. The best time to treat is in the late spring or early fall when the grass is actively growing but the heat isn’t oppressive.
Always wear protective gear, including long sleeves, pants, and chemical-resistant gloves. Follow the “label is the law” rule—using more than the recommended dose won’t kill the weeds faster; it will just kill your lawn. If you feel overwhelmed by the chemical options, don’t hesitate to call a licensed lawn care professional.
One critical warning: Avoid Quinclorac. This is a common ingredient in many “all-in-one” weed killers for lawns. While it is great for killing crabgrass in Bermuda lawns, it is absolutely lethal to St. Augustine. Always read the active ingredients list before you spray.
Mechanical Removal and Patch Repair
If you only have a few small patches of Bermuda, you might be tempted to pull them. While this is satisfying, it is often a losing battle because of those underground rhizomes I mentioned earlier. If you leave even a tiny piece of root behind, it will grow back.
A better mechanical approach is “plugging.” If you have a large area of Bermuda, you can physically dig out the entire section—soil and all—to a depth of about 6 inches. Replace that soil with fresh topsoil and install new St. Augustine sod or plugs.
This creates an immediate “wall” of healthy grass. Because St. Augustine is so thick, the new sod can often prevent any remaining Bermuda bits from reaching the surface. This is the fastest way to see results, though it requires a bit of elbow grease.
The Cardboard Smothering Technique
For those who prefer a non-chemical approach, you can try the “sheet mulching” method on localized patches. Cover the Bermuda area with a layer of heavy cardboard and weight it down with mulch. Leave it for several weeks during the summer.
This will kill everything underneath by blocking all light and air. Once the area is completely dead, you can remove the cardboard and replant your St. Augustine. It’s a patient gardener’s method, but it is very effective for organic lawn care enthusiasts.
Long-Term Prevention and Maintenance
Winning the battle is one thing; keeping the peace is another. Once you have managed to reduce the amount of bermuda grass in st augustine lawn, you must remain vigilant. Bermuda is an opportunistic plant that waits for a moment of weakness.
Keep your lawn thick! A dense turf is the best defense against any weed. When your St. Augustine is healthy, there is simply no “real estate” available for Bermuda seeds to germinate. Think of your lawn as a living shield for your soil.
Avoid scalp-mowing your edges. Many people use a string trimmer to cut the grass very short against fences or sidewalks. This “scalping” creates a perfect entry point for Bermuda grass. Keep your edges at the same height as the rest of your lawn to maintain that protective canopy.
Soil Testing for the Win
I highly recommend getting a soil test every two years. St. Augustine prefers a slightly acidic to neutral pH (around 6.0 to 7.0). Bermuda is much more tolerant of alkaline soils. By adjusting your soil chemistry to favor St. Augustine, you give your desired grass a competitive edge.
If your soil is too alkaline, you can apply elemental sulfur to slowly lower the pH. If it’s too acidic, a bit of lime can help. Your local county extension office is a fantastic resource for cheap soil testing and expert advice tailored to your specific region.
Frequently Asked Questions About Bermuda Grass in St. Augustine Lawn
Will Bermuda grass eventually go away on its own?
Unfortunately, no. Bermuda grass is a perennial, meaning it comes back year after year. Without active intervention through mowing height adjustments or chemical treatments, it will likely continue to spread and eventually dominate the sunnier areas of your yard.
Can I just spray the Bermuda patches with Roundup?
Roundup (glyphosate) is a non-selective herbicide, meaning it kills almost every green plant it touches. If you spray a patch of Bermuda with it, you will also kill the St. Augustine in that area. This will leave a brown, dead spot that will eventually be filled by more weeds unless you sod over it immediately.
How do I stop bermuda grass in st augustine lawn from coming back?
The key to long-term prevention is maintaining a height of 3.5 to 4 inches and ensuring your lawn is never stressed by underwatering. A thick, tall canopy is the most effective way to prevent Bermuda seeds from getting the sunlight they need to thrive and take over again.
Is there a “weed and feed” that works for this?
Most consumer-grade “weed and feed” products contain Atrazine, which can help. However, they are often less effective than targeted liquid sprays because the granules must be applied to wet leaves to stick, or they rely on root uptake which can be inconsistent. Targeted spot treatments are usually more effective.
Conclusion: Reclaiming Your Green Sanctuary
Transforming a lawn infested with invaders back into a lush paradise takes time, but it is incredibly rewarding. Remember that gardening is a marathon, not a sprint. Every time you set your mower blade higher and every time you water deeply, you are winning a small victory for your St. Augustine.
Don’t be discouraged if you see a few wiry stems popping up next season. Now that you know the difference between these two grasses and understand their biological weaknesses, you have the upper hand. You have the tools, the knowledge, and the plan to succeed.
Take a walk outside today, check your mowing height, and look for those tell-tale bird-foot seed heads. With a little bit of patience and the right cultural practices, your lawn will soon be the envy of the neighborhood once again. Go forth and grow!
