If you are seeing the hint of crabgrass or dandelions or any other form of weed infestation in your beautiful St Augustine grass lawn, chances are you’re already googling the best weed killers on the market. But you want to ensure you’re not getting something that could hurt your grass and the weeds.
We’ve picked our top three choices for pre-emergent and post-emergent weed killers that will not hurt your lawn.
All About St. Augustine Grass
St. Augustine is a turfgrass with lush green to blue-green tinted flat, broad blades. It has a hardiness factor of USDA zone 8-10 and is warm-season. Popular in coastal settings, it is tolerant to salt spray. It will spread through above-the-ground runners. St Augustine is very tolerant to shade conditions, but you will still want your lawn to receive at least 4 hours of sunlight for the best results.
It is typically found on the USA’s eastern coast and the Gulf Coast to the West. While native to the West Indies, Western Africa, and the Gulf of Mexico, it’s been used in the USA for lawns since the 1890s.
St. Augustine is characterized, but its distinct blades, its blue-green color (or dark green), and its tropical area thrive. It is sold by sod or plugs. There is no seed. It is highly sought after in the Florida market due to its salt tolerance and warm season usage.
How To Get Rid Of Weeds Without Killing St Augustine Grass?
Getting the best results for weed killing will depend on your lawn's current stage. Are you planting grass and do not have weeds at the moment? You’re going to be reaching for a pre-emergent.
Already seen weeds in your thick carpet of St Augustine? Then you’re going to want to grab the post-emergent weed killer. We’ve chosen our top picks of each type for the best weed killer for St Augustine grass.
Best Pre-Emergent Weed Killers For St Augustine Grass
Pre-emergent weed killers are your go-to if you don’t have weeds in your yard yet. These are usually good for 6-12 weeks and may need to be applied a second time. Here are our top choices for a pre-emergent weed killer for your St. Augustine lawn.
#1 – 0-0-7 Prodiamine Pre-emergent Herbicide Fertilizer
Coming in at #1 for our pre-emergents, the 0-0-7 Prodiamine pre-emergent fertilizer from Sunland Corporation and sold by Yard Mastery. It is safe for St Augustine grass lawns.
Pro’s of Prodiamine Pre-emergent fertilizer
- One pre-emergent to cover a wide array of weeds in your lawn
- Rain, sleet, and snow tolerant will not affect performance
We listed this as #1 simply for its versatility, price point, and ease of use. Put it into a spreader, roll it over your yard, and let the granules do their thing.
#2 – Quali-Pro Prodiamine, Pre-Emergent Herbicide, 5 lbs, Yellow Granules
Coming in at #2 on our St Augustine grass-safe pre-emergent weed killers is the Quali-Pro Prodiamine 5lb container. This bottle is fairly expensive, but it is also a lot preemergent.
Pros of the Quali-Pro Prodiamine, Pre-Emergent Herbicide
- Mixes well with fertilizers
- Has both spring and fall season use
- 65% active prodiamine, a leading choice of St. Augustine grass herbicide
We like that there is a flexible application that works against broadleaf and grassy weeds. We list it as #2 because of the price point.
#3 – Southern Ag Atrazine St. Augustine Grass Weed Killer, 1 gallon
Last on our pre-emergent weed killer list is the Southern Ag Atrazine St. Augustine Grass Weed Killer. At nearly $40 a gallon, it’s a mid-range price point for herbicides. It is the only spray on our pre-emergent top three.
Pros for Southern Ag Atrazine St. Augustine Grass Weed Killer
- Suppresses crabgrass and controls weeds from seed
- Kills several weed varieties
- Easy-to-use spray application
- It uses Atrazine, a St. Augustine-safe herbicide
We liked the easy-to-use spray bottle and that it will suppress seed weeds and crabgrass. However, it is pricey, and several gallons may need to be used throughout the season. Others on this list are at a better price point during seasonal use.
Best Post-Emergent Weed Killers For St Augustine Grass
If you’ve already seen broadleaf or grassy weeds in your yard, a post-emergent is now your best choice for a weed killer. We’ve chosen three of our favorite post-emergent weed killers that will work well on your St. Augustine lawn.
#1 – Scotts Turf Builder Bonus S Southern Weed and Feed (34.48lbs)
Our top choice for a post-emergent weed killer that will work on St. Augustine grass is this Scott's granule formula. It will cover 10,000 square feet. We chose this for several reasons.
Pros of Scotts Turf Builder Bonus S Southern Weed and Feed
- Kills a variety of weeds such as clover, dollar weed, buckhorn, burclover, black medic, chickweed, Carolina geranium, blue toadflax, and dandelions
- Perfected for St Augustine grass, including Floratam
- Large spread with 10,000 square feet per bag
This weed killer will also strengthen St. Augustine grassroots and fortify them against drought and heat
#2 – Roundup for Lawns – Ready to Use (for use on Southern Grasses) – 1 Gallon
Our second choice for post-emergent weed killer safe for St Augustine grass is the Roundup for Lawns (for use on Southern Grasses) Ready to use gallon jug. It is an inexpensive way to spot-treat your lawn.
Pros of Roundup for Lawns – Ready to Use
- Kills 93 different types of weeds such as dollar weed, clover, yellow nutsedge, and dandelion
- It comes with a longer wand for hard-to-reach areas
- Works immediately and will be rainproof within 4 hours
This is solely a weed killer and does not work to strengthen or fortify the grass roots, which made it fall to our second slot instead of the first.
#3 – Ortho Weed B Gon Weed Killer for St Augustine Grass – Ready to Spray (32oz)
Rounding out our top three is the Ortho Weed B Gon Weed Killer for St Augustine Grass. It’s inexpensive and treats around 2,500 square feet.
Pros for Ortho Weed B Gon Weed Killer for St Augustine Grass
- Kills roughly 250 types of weeds and has those weeds on the label
- Guaranteed not to harm a St Augustine lawn
- Spray, and it will be rainproof within an hour.
We like the ease of the container, it isn’t heavy, and most garden centers carry it. There is nothing to help the lawn like our top choice, and there aren’t handy features like the extended wand like our second choice. All in all, it is a solid contender, nonetheless.
Lawn Maintenance for Weed Control
Some chemical-free ways to help control weeds in your St. Augustine grass lawn. With proper lawn maintenance, you can help reduce the number of weeds you see yearly. For best results, use this lawn maintenance for weed control tips and the pre-and post-emergent weed killers listed above so that your lawn continues to be the lush, rich blue-green color without the hindrance of weeds.
A healthy and thick grass isn’t just for looks. It can decrease the pest population and create a woven chain of roots and interwoven grass blades, making it more difficult for weeds to take hold and take root.
So, in reality, the healthy, thick lawns you maintain will make it more difficult for weeds to grow, reducing your weed-killer usage. Here are the top three lawn maintenance tips to keep your St. Augustine grass weed-free and beautiful.
Mowing Your St. Augustine Grass for Less Weed Growth
Did you know that the type of St. Augustine grass you have will determine the cutting deck height for your mowing? Mowing height depends on the cultivar. This means that “Floratam,” “DeltaShade,” and “Palmetto” should be cut at a height of 3 or 4 inches, as they are taller cultivars. If you have sown a shorter or dwarf variety, of St. Augustine, such as “Delmar,” “Captiva,” or “Seville,” you’ll want to set the cutting height on your mower to 2 to 2.5 inches in height.
Don’t know what cultivar you have? Some communities have agencies that can help you, or you can mow on a 3-inch height, which is a good middle ground for whatever cultivar of St. Augustine you happen to have.
One other thing about your mowing maintenance: mowing regularly with good sharp blades. Dull blades can tangle or rip the grass out. Never mow more than 1/3 of the height at one mowing. If your grass is tall, cut at a higher setting and return to the next mowing to take more. Trauma to your lawn can set you back, and it is better to do it this way.
Watering and Irrigating your St. Augustine Grass
Watering your lawn will depend on the current weather in your location and the season. Your lawn requires only minimal watering during a winter dormancy but will need watering up to 3-4 times a week during the hot summer season. Keeping a precise watering schedule on days, it doesn’t rain will help keep your lawn looking fresh and lush.
St. Augustine grass lets you know when it is unhappy. There will be wilting and folding of the blades, turning a blue-gray instead of the rich greenish-blue hue they normally have. If you walk on your lawn and can still see footprints behind you when you are done, you probably need to water as it should snap back.
Use only ½ to 2/3 of an inch of water at one time for best watering techniques. Overwatering will lead to disease and pest problems in the future.
Fertilizing your St. Augustine Grass for Less Weed Growth
St. Augustine grass can thrive with good fertilization. To begin, wait until you are about three weeks out of the last frost threat in your area. You’ll want the soil tested to see if it needs any nutrients. If you want to save time without testing, you can’t go wrong with a good overall fertilizer like 15-5-10. For St. Augustine grass, you’ll apply about 6.5 lbs of fertilizer for every 1,000 square feet of lawn surface.
Keep to a regular fertilization schedule, once every eight weeks, for the entire growing season in your area. Water after fertilizing.
St. Augustine Grass and You
In conclusion, you’ve picked a wonderful turfgrass. It is beautiful, hardy, and gives your home years of great use. While you must treat it differently than some grasses, it’s worth it. By keeping some post-emergent weed killers in the garage and adhering to the lawn maintenance schedule we’ve outlined, your lawn will be the envy of your neighborhood. It’s all about knowing your lawn, what it needs, and giving it to it.
Should you require more help, most communities have a great Extension Service that can give you more information and updates specific to where you live. But knowing what to do and what not to do, like which weed killers work and which will burn and kill your lawn, is always good information.
What do you think?
Which is your favorite best weed killer? Let us know in the comments below which you think is best or if you have other remedies.
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