Best Weed Killers Safe for St. Augustine Grass

Dealing with weeds in your lawn can be frustrating—and if you have St. Augustine grass, it’s even trickier. That’s because this type of grass needs the same stuff weeds do (sunlight, water, soil), so it’s easy for weeds to pop up and compete for space.

And to make things more complicated, St. Augustine is picky about weed killers. Many common herbicides can actually harm your grass if you’re not careful.

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✅ Quick Answer:

The best weed killer for St. Augustine grass is Atrazine, found in products like Hi-Yield Atrazine. It’s safe for southern lawns and treats weeds like dollar weed, clover and crabgrass.

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The good news? St. Augustine grass grows thick and dense, especially varieties like Palmetto® or CitraBlue®. That thick growth helps naturally choke out some weeds. But even the healthiest lawns can still get invaded now and then—especially during the warmer months.

In this guide, we’ll walk you through:

• The most common weeds that show up in St. Augustine lawns
• Non-chemical and organic ways to keep them in check
• When and how to use herbicides safely (without killing your grass)

Important tip:
If you’ve recently planted new sod or plugs, don’t apply herbicides right away. Wait until you’ve mowed the grass at least 3–4 times. That gives it time to develop strong roots and reduces the risk of damage from chemicals.

Weed Killer Tips St. Augustine Grass Lawns

Step 1: Start With Healthy Lawn Habits (a.k.a. Cultural Control)

The first step to beating weeds? Keep your St. Augustine lawn healthy and thick. A strong lawn naturally blocks out a lot of weeds on its own.

Here’s what that looks like:

• Mow it right: Keep your grass around 2–4 inches tall. This shades out weed seeds and helps your grass win the turf war.
• Bag your clippings: This helps prevent weed seeds from spreading around your yard.
• Use your own mower: Borrowed mowers can bring in weed seeds from other lawns.
• Feed your lawn: A well-fertilized lawn grows thicker and leaves less room for weeds to sneak in. (We recommend the Lawnifi® Fertilizer Program—it’s lawn-safe and super easy to apply.)
• Hand-pull weeds when you can: It’s simple and chemical-free, but best for smaller patches or early in the season.

How to Stop Weeds Before They Start

Want to stay ahead of the weeds? Use a pre-emergent herbicide. It works like a shield in the soil that keeps weed seeds from sprouting in the first place.

When to apply:

• Spring → when soil temps hit 55°F
• Fall → when they cool down below 70°F

For lawns with St. Augustine grass, Hi-Yield Atrazine is a solid choice because it works as both a pre- and post-emergent (more on that below).

Using pre-emergents the right way saves you a ton of time, hassle and future weed pulling.

What to Use After Weeds Show Up (Post-Emergent Control)

If weeds are already showing, it’s time for a post-emergent herbicide—but be careful:
St. Augustine grass is sensitive and can be damaged by a lot of common weed killers (like 2,4-D or MSMA).

✅ What to Use Instead:

Atrazine-based herbicides (like Hi-Yield Atrazine) are your safest bet. They’re designed to:

• Kill broadleaf weeds like dollar weed, clover and chickweed
• Leave your grass healthy and green

Just be sure to read the label and follow directions carefully. Too much of a good thing can still cause stress to your lawn.

🛒 Need a Safe Weed Killer for St. Augustine?
Try Hi-Yield Atrazine Weed Killer — trusted for southern lawns. Shop now.

✅ So, What’s the Best Way to Kill Weeds Without Hurting St. Augustine?

If you want to get rid of weeds without frying your St. Augustine lawn, your safest bet is a weed killer with Atrazine—like Hi-Yield Atrazine.

It’s one of the few products that:

• ✅ Works on tough weeds like dollarweed, clover and crabgrass
• ✅ Won’t damage your lawn if applied correctly

But don’t just stop there...

The best defense against weeds is a strong, healthy lawn. Keep your St. Augustine grass in good shape by:

• Mowing regularly
• Feeding it with the right fertilizer
• Watering consistently

Healthy grass = fewer weeds, less work and better curb appeal.

Frequently Asked Questions: Weed Killers & St. Augustine Grass