When you’re growing St. Augustine grass, weeds can feel like an endless battle. A good solution is to choose the best weed killer for St. Augustine grass—one that keeps the lawn green without damaging the turf.
In this guide we’ll cover the top products, how to apply them, and the science behind why some work better than others.
Let’s dive into the most reliable, effective, and lawn‑friendly options for 2024.
Understanding How St. Augustine Grass Responds to Herbicides
Why St. Augustine Requires Special Care
St. Augustine grass is a warm‑season turf that thrives in heat and humidity. However, it is sensitive to certain herbicides that can cause brown patches or stunted growth.
Choosing a weed killer that targets common weeds like crabgrass, dandelion, and clover while sparing St. Augustine is essential.
Key Factors in Herbicide Selection
When looking for the best weed killer for St. Augustine grass, consider:
- Target weed spectrum
- Pre‑emergence vs post‑emergence action
- Turf safety and residual activity
- Ease of application and cost
Common Weed Types in St. Augustine Lawns
Typical weeds in St. Augustine lawns include:
- Crabgrass
- Dandelion
- Clover
- Bindweed
- Annual bluegrass
Top Product Reviews: Best Weed Killer for St. Augustine Grass in 2024
1. Scotts Turf Builder Weed & Feed
Scotts Turf Builder combines a pre‑emergence herbicide with a nitrogen fertilizer.
It prevents crabgrass and broadleaf weeds while feeding your lawn.
Safe when applied to St. Augustine, but be cautious about over‑fertilization.
2. Spectracide Weed Stop
This post‑emergence product targets a wide range of weeds.
It contains a selective herbicide that won’t harm St. Augustine.
Spray evenly for best results.
3. Ortho Advance 4‑Week Weed Control
Ortho Advance offers a 4‑week protection window.
Its active ingredient, pendimethalin, is effective against crabgrass and dandelion.
Use during the early growing season.
4. Pioneer 2‑Step Weed & Feed
Combines a broadleaf and grassy weed control with a 6‑month fertilizer.
It’s ideal for summer lawns that need extra nutrients.
5. Green Thumb 4‑In‑1 Weed Control
This product tackles crabgrass, yellow nutsedge, and dandelion.
It’s formulated to be safe for St. Augustine.
6. Roundup Ready St. Augustine Care
Roundup Ready is a post‑emergence spray that kills weeds on contact.
It’s highly effective but use it sparingly to avoid turf damage.
7. Southern Ag 10‑Day Crabgrass & Corn
Specifically designed for Southern U.S. lawns.
It offers a 10‑day protection period against crabgrass.
8. Advance Weed-B-Gone
Targets broadleaf weeds like dandelion.
It’s a non-selective option—use only on bare spots.
9. Weed Hack St. Augustine Formula
A newer product with a unique blend of herbicides.
It offers a 12‑week residual kill.
10. Seasol St. Augustine Lawn Care
Not a herbicide, but a seaweed nutrient that promotes turf health.
Healthy grass is naturally more resistant to weed invasion.
How to Apply the Best Weed Killer for St. Augustine Grass
Timing is Everything
Apply pre‑emergent in early spring or early fall.
Post‑emergent works best when weeds are small, usually 1‑2 inches tall.
Preparing Your Lawn
- Mow to 2.5–3 inches.
- Water lightly 24 hours before application.
- Remove debris and dead grass.
Using a Sprayer or Spreaders
For liquids, use a backpack sprayer for even coverage.
For granules, use a broadcast spreader; then water in within 48 hours.
Post‑Application Care
Keep pets and children away for at least 24 hours.
Water the lawn 3–4 days after application if the forecast calls for dry weather.
Comparison Table: Best Weed Killer for St. Augustine Grass 2024
| Product | Type | Weed Spectrum | Residual Time | Turf Safety |
|---|---|---|---|---|
| Scotts Turf Builder | Pre‑emergent + fertilizer | Crabgrass, broadleaf | 1–2 weeks | High |
| Spectracide Weed Stop | Post‑emergent | All common weeds | Immediate | High |
| Ortho Advance 4‑Week | Pre‑emergent | Crabgrass, dandelion | 4 weeks | High |
| Pioneer 2‑Step | Pre + post | Broadleaf + grassy | 6 months | High |
| Roundup Ready | Post‑emergent | Broadleaf | Immediate | Moderate |
Expert Pro Tips for Maintaining a Weed‑Free St. Augustine Lawn
- Use a pre‑emergent only once per season—over‑application can damage the turf.
- Apply post‑emergent during the first rainy season to allow the chemical to be rinsed into the soil.
- Maintain mowing at 2.5–3 inches; taller grass shades weeds.
- Use a lawn aerator every 3–4 months to improve root health.
- Incorporate a balanced fertilizer just before the growing season.
- Regularly inspect for new weed patches and spot‑treat promptly.
- Keep a log of applications to avoid overlapping chemicals.
- Consider a natural mulch around trees to reduce weed seedlings.
Frequently Asked Questions about best weed killer for St. Augustine grass
What is the safest weed killer for St. Augustine grass?
Scotts Turf Builder or Pioneer 2‑Step are considered safe due to their selective formulas.
Can I use Roundup on St. Augustine?
Roundup is non‑selective; use it only on bare spots or treat with caution around the lawn.
How often should I apply pre‑emergent weed control?
Once in early spring and once in early fall is typical for most climates.
Will fertilizer kill weeds?
Fertilizer promotes turf health, making it more resistant to weeds, but it does not kill existing weeds.
What are the signs of herbicide damage?
Yellow or brown patches, stunted growth, or a general loss of vigor in the lawn.
Is organic weed control effective?
Organic options like vinegar or corn gluten meal can control some weeds but are less potent than synthetic herbicides.
Do I need to water after spraying weed killer?
Yes, water lightly within 24–48 hours unless the rain is expected.
Can I use the same product for both crabgrass and dandelion?
Yes, products like Ortho Advance target both.
How long does the effect last?
Pre‑emergent lasts up to 4 weeks; post‑emergent has immediate action but may require repeat applications.
What should I do if weeds return?
Spot‑treat with a post‑emergent or repeat the pre‑emergent if the season allows.
Choosing the right product and applying it correctly will keep your St. Augustine lawn lush and weed‑free. Follow the steps above, stay consistent, and enjoy a vibrant yard all year long.
