St. Augustine vs. Bermuda Grass (Turf Control)

Choose the grass you want to keep before you treat the one you do not. St. Augustine needs a much higher cut than Bermuda, so lowering the mower is not a safe way to control an invasion. Identify the grasses, protect the retained lawn, then use careful edging, mowing, and only label-approved treatment.

When Bermuda runners enter St. Augustine, or St. Augustine spreads into Bermuda, the right fix depends on which turf you want to keep. The grasses grow differently and need different mowing heights. A control method that helps one lawn can thin or kill the other.

I start with three questions: What grass is wanted? How mixed are the two grasses? Can the unwanted grass be removed without exposing the desired turf to damage? Answering these first can prevent wasted treatment and costly lawn repair.

Identify the grass and set the control goal

Correct identification means confirming which turf is spreading before you mow, dig, or apply a product. St. Augustine and Bermuda can both spread by above-ground runners, so look at leaf width, growth habit, and underground stems as well as the overall look of the lawn.

St. Augustine usually has broader blades and thick above-ground runners, called stolons. Bermuda has finer blades and can spread by both stolons and underground stems, called rhizomes. These clues help, but appearance can vary by cultivar and growing conditions. If the grass is hard to identify, ask a local extension office or qualified turf professional before treating it.

Then mark the grass you want to retain. Mark lawn edges, trees, drains, irrigation heads, and sensitive plants near the invaded area. This matters most when the grasses are intertwined: a product that kills the unwanted grass may also injure the desired one.

The control plan should follow the grass you are keeping, not the grass you are trying to suppress.

Equipment setup, grass identification, and site safety

Equipment setup means choosing a mower height and tools that suit the retained grass, then preparing the area to limit injury and spread. Use a rotary mower for taller Bermuda and St. Augustine. Fine-textured hybrid Bermuda kept very low often needs a reel mower and cultivar-specific care.

These are general ranges, not a substitute for cultivar-specific guidance. Set the mower for the retained turf. Do not lower St. Augustine to Bermuda height to try to starve Bermuda; scalping stresses St. Augustine and does not reliably remove the invader.

Before work, check the product label and local pesticide rules if chemical treatment is being considered. Wear the protective gear listed on the label, keep people and pets out of the work area, and avoid mowing wet turf. A sharp, balanced blade makes a cleaner cut and reduces strain on the mower.

Field operation: containment, mowing, and targeted control

Containment means slowing the unwanted grass at its edge while you choose a safe removal method. A clean edge and hand removal of isolated runners can help where the invasion is small. For dense, interwoven turf, avoid assuming that mowing or a quick spray will separate the grasses.

Start by tracing the boundary between the two grasses. Cut a clear edge where practical, then lift or cut isolated runners and roots without pulling up large areas of desired turf. Bag or dispose of removed material in a way that prevents live runners from rooting elsewhere. Clean tools before moving to another lawn area.

Mowing supports healthy retained turf but is not a stand-alone cure for an established invasion. Follow the one-third rule: remove no more than one-third of the leaf height in one mowing. If the lawn is overgrown, reduce its height over several mowings rather than cutting it very short at once.

Chemical control is more complex because selectivity depends on the exact product, grass species, cultivar, and site. “Selective” does not mean safe on every lawn. Read the current label for the exact turf species, target weeds or grasses, site, rate, weather limits, application method, and re-entry interval. Never transfer a rate or instruction from a different product or formulation.

Glyphosate is nonselective. It can kill either grass it contacts, so do not broadcast it through mixed turf. If the label allows a spot treatment, protect desirable grass with a shield and use only the labeled method. Do not spray in wind, allow drift, or let spray run toward drains or other sensitive areas. Overspray can leave dead patches or kill surrounding lawn.

Where runners are tightly mixed, there may be no practical way to treat only one grass with a product. You may need to remove and renovate a section rather than risk injury across the lawn. Check local rules before applying pesticides; requirements can vary by location.

Mowing and control choices by lawn situation

Mowing height is the cutting height that supports the retained grass, not a direct treatment for the invading grass. Keeping the lawn at the suitable height can reduce stress on the desired turf, but it will not guarantee that the other grass disappears.

Consider these typical field situations. They are planning examples, not reports of specific properties.

In each case, consider how much of the lawn is affected and how much desired turf could be lost. A small isolated patch may justify careful hand removal. A large, mixed area may call for a planned renovation. Compare the likely repair work before choosing a treatment.

Maintenance, mower blade care, and treatment follow-up

Follow-up means checking whether the unwanted grass returns and restoring bare spots without spreading runners. A single mowing or treatment may not end an invasion. Keep notes on the treated area, date, product directions followed, and any visible regrowth.

Clean mower decks and tools after work in invaded turf. Live runners or plant pieces can be carried to another part of the property. Keep blades sharp and balanced, and mow dry grass where possible. These steps support an even cut and help limit accidental spread.

After a chemical application, follow the label’s watering and re-entry directions exactly. Retreatment is appropriate only if the label permits it, at the stated interval and under its conditions. Do not apply extra product because the first treatment seems slow.

If control leaves bare soil, restore it with the desired turf using a locally suitable method. Keep the new area protected while it establishes, and check the boundary often for returning runners. For a large or valuable lawn, local turf advice can help match the repair method to the grass and growing conditions.

Storage, product handling, and seasonal lawn recovery

Safe storage and recovery protect people, pets, turf, and nearby areas after the work is done. Keep pesticides in their original labeled containers and follow the label’s storage and disposal instructions. Do not pour leftover product into a drain or onto soil unless the label specifically directs it.

Wait to judge the result until the label’s stated timing and conditions allow it. Weather, grass growth, and the treatment method can affect what you see. If the retained grass shows injury, stop further treatment and check the label for first-aid or spill directions; seek local professional advice when needed.

Plan repair around the retained grass’s active growth and local conditions rather than a fixed calendar date. Avoid stressing a weakened lawn with a severe cut or repeated treatment. The goal is a stable boundary and a healthy stand of the grass you chose to keep.

Frequently asked questions

These answers cover common decisions when one grass is spreading into the other. Check local guidance and current product labels before any pesticide use, because approved uses and directions depend on the exact product and site.

Can I mow Bermuda low to get rid of it in St. Augustine?
No. Cutting St. Augustine to Bermuda height can stress or scalp it and does not reliably eliminate Bermuda. Keep the retained St. Augustine at its suitable height.

What height should I mow St. Augustine?
A general range is 3.5–4 inches (89–102 mm). Follow guidance for your cultivar and local growing conditions.

What height should I mow Bermuda?
A general rotary-mower range is 1–2 inches (25–51 mm). Fine-textured hybrid Bermuda kept shorter often needs a reel mower and cultivar-specific care.

Will glyphosate kill either grass?
Yes. Glyphosate is nonselective and can kill either grass it contacts. Do not spray it across mixed turf.

Is there one herbicide that removes Bermuda from St. Augustine safely?
There is no universal product or rate that is safe across all cultivars and conditions. Use only a product labeled for the exact turf, target, and site.

Can I spray when the grasses are growing together?
Only if the product label allows a method that can protect the desired grass. Do not broadcast a nonselective herbicide through mixed turf or spray in wind.

How much grass can I cut off at once?
Follow the one-third rule: remove no more than one-third of the leaf height in one mowing. Lower overgrown turf in stages.

What should I do if the grasses are fully mixed?
Compare careful removal and renovation with the risk of harming the retained turf. A local turf professional or extension office can help confirm the grass and options.

When can people and pets return after treatment?
Use the product label’s re-entry interval. Do not rely on directions from another product.

How do I stop runners from spreading on the mower?
Clean the mower deck and tools after working in invaded areas, and remove live plant pieces before mowing elsewhere.

(This article was written by one of our staff writers, Victor Dempsey. Visit our Meet the Team page.)