It’s important to understand the right and wrong ways to apply weed-and-feed products and herbicides to St. Augustine grass. Many broadleaf weed killers also harm St. Augustine grass. In fact, only a few herbicides on the market are rated to treat St. Augustine without harming it, but most of them are weed control products only — not weed-and-feed products. 


    I have a few initial thoughts about weed-and-feed products. 

    Unless you live in a frost-free climate, you should stop using any fertilizers at least six weeks before your average first frost date. St. Augustine is a warm-season grass that goes dormant for the winter, and you don’t want to stimulate growth that front can kill.

    Weed-and-feed products are best reserved for spring and summer applications for these types of lawns.

    The most common herbicide for St. Augustine lawns is Atrazine. Simply put, Atrazine is nasty stuff. It is a possible cancer-inducing chemical that could also cause birth defects, and it shows up in alarming levels in drinking water. One look at the stern warnings on the label should make you think twice about putting it on your lawn.

    person applying weed killer to a lawn

    A healthy lawn is naturally weed-resistant. If you have a widespread weed problem, focus on keeping your lawn healthy or on replacing the unhealthy lawn with groundcover or planting beds.

    Weed-and-feed products contain both fertilizer and herbicide in one formulation. The combination can provide convenience but needs proper precautions.

    When to Avoid Weed and Feed

    Weed-and-feed products contain fertilizer and herbicide. The combination works well for reviving St. Augustine grass but carries some risk. Here are reasons to avoid putting weed and feed on St. Augustine grass:

    • It’s fall or winter. The fertilizer component can stimulate growth that is susceptible to frost damage. Instead, reserve weed and feed for the active growing seasons of spring and summer.
    • It’s six weeks or less before your average first frost date. Find your average first frost date from the Farmer’s Almanac, and don’t apply a weed-and-feed product in this six-week window. This way, you give your grass time to harden off before cold weather arrives.
    • Don’t apply during a drought or heat stress. Fertilizers can push growth that requires more water than the lawn is getting. This practice leads to grass burnout.
    • Don’t apply it if you’re overseeding. The herbicide component will inhibit the germination of grass seed. Wait until new grass is established before applying weed and feed.
    • Don’t spread on newly laid sod. The chemicals can leach into the soil under the sod and inhibit root establishment. Let new sod take root for four to six weeks before applying a weed and feed product.
    Today’s Homeowner Tips

    Proper timing is important when using these combination products on St. Augustine grass. Pay attention to weather patterns and the health of your lawn.

    The above timing recommendations are specific to warm-season grasses like St. Augustine. Cool-season grasses may have different guidelines, so always check the product label.

    Problems with Atrazine

    Atrazine is an herbicide commonly found in weed-and-feed products marketed for St. Augustine grass. However, there are good reasons to avoid this chemical:

    • The U.S. Environmental Protection Agency (EPA) classifies Atrazine as a possible carcinogen and endocrine disruptor. Studies show links to increased cancer rates in people with high exposure.
    • The chemical persists in soil and groundwater. It has contaminated drinking water sources across the country.
    • Atrazine runoff contributes to toxic algae blooms in ponds, lakes, and other surface waters, creating a hazard for pets and wildlife.
    • Many countries have banned Atrazine. It is not banned in the United States, but some states set partial bans or restrictions.

    Over the years, I transitioned away from Atrazine to safer options, such as corn gluten meal, vinegar, and plant-based herbicides. These have less environmental impact.

    Given the health and environmental risks of Atrazine, avoiding it may be the wisest choice for you, your lawn, and your community. Talk to your lawn care company about chemical-free options or products without Atrazine.

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    Maintaining a Healthy Lawn

    The best defense against weeds is a healthy, thriving lawn. Here are some tips:

    • Mow your lawn at the proper height for your grass type. Proper mowing height encourages deeper root growth. Keep mower blades sharp for clean cuts. 
    • Water thoroughly and infrequently to encourage deep root growth. Avoid frequent, light watering. Deep watering promotes stronger grass plants.
    • Dethatch and aerate your lawn annually to alleviate soil compaction. Thatch removal improves air and nutrient flow to the soil.
    • Apply a slow-release fertilizer two to three times a year. I recommend natural organic options like organic fertilizers break down slowly for steady feeding.
    • Overseed bare patches in spring and fall. Cover the new seed with straw. Seeding fills in thin and bare areas.
    • Raise your mowing height before the summer heat and lower it for fall. Adjusting height helps the grass stay healthy in changing weather.
    • Apply corn gluten meal in spring to deter new weed seedlings. Corn meal inhibits root formation in emerging weeds.

    With proper cultural practices, your lawn can out-compete weeds. Then spot treatments or hand weeding may be all you need for problem areas.

    FAQs About Applying Weed and Feed to St. Augustine Grass

    When is the best time to apply weed and feed?

    For St. Augustine grass, apply weed and feed during the active growing season of spring and summer. Avoid use in fall and winter. Discontinue at least six weeks before your average first frost.

    How often can I apply weed and feed products?

    You can apply most products every six to eight weeks during the growing season. Do not exceed the labeled application frequency and annual use limits.

    What precautions should I take when using weed and feed?

    Read the label thoroughly and follow all instructions. Wear gloves, long sleeves, and closed-toe shoes when handling the product. Keep children and pets off-treated areas until the lawn is dry. Sweep any product that lands on driveways back onto the lawn to prevent runoff.

    Are weed-and-feed products safe for the environment?

    Some common herbicides in weed-and-feed products, like Atrazine, are linked to environmental harm. Some countries have banned the use of Atrazine as a result. Consider alternatives like corn gluten meal or natural weed killers instead.

    Can I use weed and feed on newly laid sod or after overseeding?

    Avoid using a weed-and-feed product on new sod or after seeding new grass. Wait four to six weeks for new sod to root before applying weed and feed. Allow new seedlings to fully establish before treatment as well.

    Further Reading

    Editorial Contributors
    avatar for Coty Perry

    Coty Perry

    Expert Writer & Reviewer

    Coty Perry is a lawn and garden writer for Today’s Homeowner. He focuses on providing homeowners with actionable tips that relate to the “Average Joe” who is looking to achieve a healthier and greener lawn. When he isn’t writing he can almost always be found coaching youth football or on some trail in Pennsylvania in search of the next greatest fishing hole.

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    photo of Sabrina Lopez

    Sabrina Lopez


    Sabrina Lopez is a senior editor for Today’s Homeowner with over 7 years of writing and editing experience in digital media. She has reviewed content across categories that matter to homeowners, including HVAC services, home renovations, lawn and garden care, products for the home, and insurance services. When she’s not reviewing articles to make sure they are helpful, accessible, and engaging for homeowners like herself, Sabrina enjoys spending time with her family and their two parrots.

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