Will St. Augustine Take Over Bermuda Grass? It’s Complicated

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Sydney has over 15 years of experience in lawn maintenance, landscape design, and organic gardening. She has an A.A.S. in Landscape Design/Organic Produce Production from the Nebraska College of Technical Agriculture.

St. Augustine vs. Bermuda

Both St. Augustine and Bermuda are warm-season turfgrasses that will grow vigorously and fill in quickly under the right circumstances. However, they are unique grasses that need very different maintenance schedules in order to form a healthy lawn.

St. Augustine Grass

This is a sod-forming turf, meaning it spreads through above-ground stolons that root into the soil. This allows it to spread quickly and repair itself easily. These stolons make St. Augustine an aggressive turf that is able to choke out weeds and other grasses if it is maintained properly.

St. Augustine is the most shade-tolerant warm-season grass. It grows in the warm-season grass zone, which covers southern New Mexico and Arizona, most of Texas, Louisianna, Mississippi, Alabama, southern Georgia and South Carolina, and all of Florida.

Plant Profile:

Mower Height: 2.5”-4”
Irrigation: 1” only when lawn shows drought stress
Fertilizer: 2lbs-4lbs of nitrogen/growing season/1,000sq’
Common Pests: Chinch bugs, brown patch, gray leaf spot

Bermuda Grass

Bermuda is also a sod-forming turf, although it spreads with both stolons and rhizomes. Stolons grow across the ground filling in bare patches of soil, while rhizomes grow underneath the ground establishing root systems that spring up new leaves. This growth pattern makes Bermuda a more aggressive sod grass than St. Augustine in most climates, which is why it is commonly used in sports applications.

Bermuda is not shade-tolerant. In fact, it needs to be mowed very short so that it doesn’t shade itself out and die. It also has a wider range of growth. Bermuda grows in the warm-season grass zone and the transition zone, meaning it can thrive in the lower 2/3rds of the United States.

Plant Profile:

Mower Height: 1”-2”
Irrigation: 1” only when lawn shows drought stress
Fertilizer: 2lbs-4lbs of nitrogen/growing season/1,000sq’
Common Pests: Large patch, dollar spot, spring dead spot

Managing Bermuda Grass In a St. Augustine Lawn

If you live in the subtropical/tropical area of the United States, you will likely want a St. Augustine lawn while keeping the Bermuda grass at bay. This can be difficult since Bermuda is more aggressive and cold-hardy, and cannot be sprayed without damaging the turf you wish to keep.

Bermuda’s kryptonite is shade. The easiest way to encourage St. Augustine is to keep the mower set high. Mow your lawn at 4” twice per week with a sharp blade. The taller blades of grass will shade out the Bermuda, and a sharp blade will ensure a clean cut, which means healthier plants (source).

Don’t bag your grass clippings. Allow your clippings to fall back onto the soil when you mow. This adds nitrogen back into the ground, and it also helps to shade out the Bermuda grass.

Don’t use St. Augustine in high-traffic areas. If a portion of your lawn is constantly trampled, Bermuda will quickly fill in the bare patches. Bermuda is more aggressive, so it will create a stronghold in well-traveled areas. From there, it will continue to try to spread into the rest of your lawn, which will create a never-ending battle between the two grasses.

*For high-traffic areas, try installing a patio or placing a lawn mat on the ground to prevent weeds and other grasses from taking hold.

Using Bermuda Grass To Establish a St. Augustine Lawn

If you live in a region where St. Augustine is especially happy, you may be able to use Bermuda to your advantage. It is expensive to establish St. Augustine because it can only be planted with sprigs, plugs, and sod. However, you can plant Bermuda with seed, and establish a green lawn fairly quickly due to its aggressive nature.

So, many homeowners choose to seed Bermuda grass to get a thick stand of green grass. This helps to hold freshly-prepared soil in place, and allows the lawn to take in water without creating mud puddles. They will also plant St. Augustine sprigs along with the seed. These sprigs take longer to root and grow, but once they take hold, they will quickly spread and shade out the Bermuda.

This technique only works in the more hot, humid parts of the warm-season grass zone. The farther north you live, the more likely Bermuda will take over because St. Augustine cannot tolerate cooler temperatures.

Managing St. Augustine Grass In a Bermuda Lawn

Now, if you have a Bermuda grass lawn, but you live in a hot, humid area, you will likely have St. Augustine trying to creep in and take over. This is especially true for areas of your lawn that are shaded. It is impossible to establish Bermuda in a shady area, but you can keep a (mostly) pure stand of turf if you follow the correct maintenance schedule for your lawn.

St. Augustine can’t survive short mower heights (source). However, without the proper lawn mower, Bermuda can’t, either. Bermuda thrives between 1” and 1.5”, but this is an impossible height with most push mowers. When the mower is set this low, the fittings that hold the blade in place will dig into the ground, and you will scalp your lawn. The grass dies, and weeds take over.

Use a reel mower. Yes, like the antique style lawn mower. Reel mowers allow you to get a close, clean cut for low-growing grasses. This keeps the lawn healthy, which allows it to maintain a thick carpet over the soil, choking out St. Augustine.

Mow more frequently. Reel mowers can’t cut as much at one time as push mowers, which means you need to mow more often. This also allows the clippings time to break down, since they are smaller and a lower volume per mowing. This will help prevent thatch buildup which can shade out and kill Bermuda.

*You should still remove thatch once per year by either raking in the spring, or bagging your clippings the first time you mow for the season. Click here to read about dethatching St. Augustine grass.

Management Techniques For Unwanted Grasses

One of the most difficult parts of keeping a pure stand of turf is that herbicides formulated for grass will kill all grass. It’s impossible to spray and kill the invasive grasses without killing your own lawn. This only leaves bare patches of soil, which is prime real estate for weed seeds to germinate, compounding the issue.

Pulling grass is almost as damaging. For sod-forming grasses, pulling up roots and runners only encourages new growth. Many grasses will sprout from small pieces of roots left in the soil, meaning each time you pull one plant, you may be creating five.

The only way to effectively manage invading grasses is to tailor your lawn’s maintenance schedule to help your own turf thrive. This will include:

Annual soil tests to determine pH and nutrient values, and amending as needed
Evaluating the soil’s texture and amending as needed
Creating a turf-specific irrigation schedule
Mowing at the correct height
Sharpening your mower blade at least once per season, or monthly if possible

All grasses have specific maintenance requirements in order to thrive, and a thriving yard can fight off invading grasses without much intervention on your end.

For more information on how to install a new lawn, improve soil quality, or care for your current turf grass, please visit our other lawn articles to learn how you can create your own thriving yard.

Looking for an alternative to St. Augustine? Read Centipede Grass Vs. St. Augustine – Pros And Cons Of Each