How to Get Rid of Weeds in St. Augustine Grass Without Killing Your Lawn

Getting weeds out of a St. Augustine lawn is harder than it looks, and the reason is simple: St. Augustine is sensitive to several of the weed killers sold for "lawns." A product that works fine on a northern bluegrass lawn can thin or kill Floratam. So the goal is not just killing weeds, it is killing weeds without killing the grass you already paid for.

Here is what actually works on Central Florida lawns in Saint Cloud, Lake Nona, Kissimmee, Orlando, and Apopka, in the order you should do it.

Why St. Augustine makes weed control tricky

Three things set St. Augustine apart from other turf:

1. It reacts badly to some common broadleaf herbicides. Products built around 2,4-D-type chemistry can injure St. Augustine, especially in heat. Always read the label for the words "St. Augustinegrass" before anything touches your yard.
2. Nonselective products kill it outright. Glyphosate (the active ingredient in many "kill everything" sprays) does not know the difference between dollarweed and Floratam. Use it only for spot-killing in beds or cracks, never across turf.
3. Timing collides with Florida's fertilizer rules. Many "weed and feed" products are half fertilizer, and several Central Florida counties restrict nitrogen and phosphorus fertilizer during the summer rainy season. That makes the most convenient product the hardest one to use legally at the time you most want it. See our guide to the Florida summer fertilizer ban for the county-by-county detail.

First, identify what you actually have

The right product depends entirely on the weed category. These three groups need three different chemistries, and this is where most DIY money gets wasted.

A quick field trick for sedges: roll the stem between your fingers. Sedge stems are triangular, grass stems are round. If it rolls unevenly and feels edged, you are dealing with nutsedge, and a standard broadleaf weed killer will do nothing.

Dollarweed is the single most common call we get in this area, and it usually points at a watering problem rather than a weed problem. We wrote a dedicated guide: how to get rid of dollarweed in St. Augustine.

The real fix: a thick lawn is the best weed killer

This is the part homeowners skip, and it is the part UF/IFAS puts first. Their weed management guidance is blunt about it, the presence of weeds is generally a result of a weakened turf stand, not the cause of it. Weeds colonize thin, stressed, or bare turf. Fix the thinness and you remove most of the opportunity.

Three cultural practices do the heavy lifting:

• Mow high. Standard St. Augustine cultivars want roughly 3.5 to 4 inches. Tall grass shades the soil surface, and weed seeds that never get light never germinate. Cutting short to "stretch time between mows" is the fastest way to invite weeds. More detail in our Florida lawn mowing guide.
• Water deeply and infrequently. Shallow daily sprinkling grows shallow roots and keeps the surface damp, which favors dollarweed and sedges. Water on your allowed days only, see Central Florida watering days.
• Fertilize on schedule. A properly fed lawn out-competes weeds. Our Florida fertilizing schedule covers timing.

If your lawn is more weed than grass, say, over about half the area, herbicide is the wrong tool. At that point you are maintaining a weed population, not a lawn, and sod installation is usually cheaper than two seasons of chasing it with chemicals.

Pre-emergent: the Central Florida timing cheat sheet

Pre-emergent herbicide stops weed seeds as they germinate. It does nothing to weeds you can already see. That makes timing everything: a week or two late and you have paid for nothing.

Spring application

UF/IFAS guidance puts the Central Florida window around February 15 (it is roughly February 1 in South Florida and March 1 in North Florida). The temperature-based rule is more reliable than the calendar: apply before daytime temperatures reach about 65 to 70°F for four or five consecutive days, which is when summer annual weed seeds start moving.

One exception worth knowing: goosegrass germinates later than crabgrass. If goosegrass is your problem weed, delay that application by about three to four weeks.

Fall application

The fall window opens when nighttime temperatures drop to about 55 to 60°F for several consecutive days: typically late October into early November here. This one catches the cool-season weeds that show up in winter lawns.

Pre-emergent rules that keep you out of trouble

• Do not apply to newly laid sod. Pre-emergents inhibit root development. Wait until the sod has fully rooted.
• Water it in according to the label. An unwatered pre-emergent sits on top of the thatch and does nothing.
• Do not apply if you plan to plant grass seed or plugs in that area soon.

Post-emergent: what is safe on St. Augustine

Post-emergent products treat weeds that are already up. This is where label-reading matters most.

Generally usable on St. Augustine when the label says so:

• Atrazine-based products are labeled for St. Augustinegrass and are a common choice for broadleaf weeds and some sedges. Two cautions: heat raises the risk of turf injury, so follow the label's temperature restrictions, and atrazine is restricted or regulated in some areas, check before you buy.
• Sedge-specific herbicides for nutsedge and kyllinga. Nutsedges are among the most damaging sedge weeds and simply will not respond to broadleaf products.

Use with real caution, or avoid:

• 2,4-D-heavy mixes. Risk of injury to St. Augustine, particularly in warm weather.
• Dicamba near trees and shrubs. It can be taken up through the roots of desirable plants and cause serious damage well away from where you sprayed.
• Anything nonselective (glyphosate and similar). Spot use only, off the turf.
• Any application during peak summer heat. Herbicide injury risk rises sharply with temperature. Treat in milder weather when you can.

And do not overlook hand-pulling. For a dozen dollarweed plants or a few clumps of nutsedge, pulling (roots and all, in moist soil) is faster, cheaper, and zero-risk compared to spraying the whole lawn.

What about "weed and feed"?

Weed and feed is convenient and frequently the wrong call in Central Florida, for two reasons.

First, the timing rarely lines up. The weeds show up in the warm, wet months, which is exactly when several Central Florida counties restrict nitrogen and phosphorus fertilizer application. Second, the two jobs want different timing anyway: your lawn's best fertilizer window and your best herbicide window are usually not the same week. Applying both because they came in one bag means one of them is mistimed.

Separating the two, feed on the lawn's schedule, treat weeds on the weeds' schedule, gets better results from both.

A year-round weed control rhythm for Central Florida

Our Central Florida lawn care calendar puts this alongside the rest of the year's tasks.

DIY or hire it out?

DIY makes sense when the weed pressure is light, you have correctly identified the weed, and you are willing to read labels carefully. Expect to buy at least a pre-emergent, a broadleaf product, and a sedge product, three purchases, three timings.

Hiring it out makes sense when the lawn is more than lightly infested, when you have already had a bad experience with turf injury, or when you would rather not store and time three chemicals. A professional fertilization and weed control program handles identification, product selection, timing, and application rate together, and the identification step is where most DIY attempts go wrong. You can see our program pricing on the pricing page.

Either way, the cultural practices are non-negotiable. No spray program compensates for a lawn mowed too short and watered too often.

Frequently asked questions

How do I get rid of weeds without killing my St. Augustine grass?

Use products whose label specifically lists St. Augustinegrass, match the product to the weed type (broadleaf, grassy, or sedge), and avoid applications in peak heat. Then fix the underlying thinness, mowing at 3.5 to 4 inches and watering deeply but infrequently prevents far more weeds than any spray.

Will St. Augustine grass choke out weeds on its own?

A dense, healthy St. Augustine lawn is genuinely competitive and will crowd out many weeds. That is why UF/IFAS frames weeds as a symptom of weakened turf. But it will not out-compete an established stand of nutsedge or torpedograss without help.

Is atrazine safe for St. Augustine grass?

Atrazine is labeled for use on St. Augustinegrass, which is why it is common in Florida. "Labeled" is not the same as "risk-free", follow the label's temperature restrictions and rates, since heat increases the chance of turf injury. Availability is also regulated in some areas.

Can I use weed and feed on St. Augustine grass in Florida?

You can, but it is often the wrong tool here. Summer fertilizer restrictions in several Central Florida counties collide with peak weed season, and the ideal timing for feeding and for weed control usually differs. Treating them as two separate jobs works better.

When should I apply pre-emergent in Central Florida?

Around mid-February for the spring application, or when daytime temperatures hold at 65 to 70°F for four or five consecutive days, whichever comes first. Add a fall application when nights settle at 55 to 60°F, usually late October to early November.

Why does my St. Augustine lawn have so many weeds?

Almost always because something thinned the turf first: mowing too short, watering too often and too shallowly, compaction, shade, or unaddressed pest and disease damage. Weeds fill the gap that stress created.

Will vinegar or a home remedy kill weeds without killing my grass?

No. Vinegar-based and salt-based home remedies are nonselective, they damage whatever they contact, including St. Augustine. They also typically burn the top growth without killing the root, so the weed returns.

Will Roundup kill St. Augustine grass?

Yes. Glyphosate is nonselective and will kill St. Augustine along with the weed. Use it only for spot treatment in beds, gravel, or cracks, never as a broadcast application on turf.

Getting help with a weedy lawn

If you are in Saint Cloud, Lake Nona, Kissimmee, Orlando, or Apopka and your lawn has gotten away from you, we are happy to look at it. Identification is free and it is the step that determines everything else. Request an estimate and we will tell you honestly whether you need a treatment program or a fresh start.

Sources: University of Florida IFAS Extension, "Weed Management Guide for Florida Lawns" (EP141), and UF/IFAS Gardening Solutions guidance on St. Augustinegrass. Always follow the product label, the label is the law.