How To Kill Crabgrass in St Augustine Grass

How To Kill Crabgrass in St Augustine Grass

How to kill crabgrass in St Augustine grass? This question bothers many individuals having St Augustine grass on their lawns. Don’t worry; we’ve covered you with practical solutions and preventative measures to restore your lawn’s health.

How To Kill Crabgrass in St Augustine Grass: 

  • AgraLawn Crabgrass Killer 
  • Solitaire Crabgrass Killer 
  • Scotts Step 1 Crabgrass Preventer 
  • Greenyard Crabgrass Preventer 
  • Trimec Crabgrass Plus 
  • Zamzows Defendz Crabgrass Preventer.
  • Baking Soda (with caution)


Dive in to learn more about how you can effectively identify, control, and prevent crabgrass infestations in your St. Augustine lawn.

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Crabgrass, scientifically known as Digitaria, is a warm-season annual weed germinating when soil temperatures reach about 55-60 degrees Fahrenheit and continues growing throughout the summer. It spreads aggressively, each plant producing up to 150,000 seeds during its lifecycle. The plant dies as the first frost hits, but the seeds remain dormant in the soil, ready to germinate the following spring.

St. Augustine grass, a popular lawn choice due to its thick, carpet-like growth and tolerance to heat, is particularly susceptible to crabgrass invasions. Crabgrass, an opportunistic plant, takes advantage of any weakness in your lawn. If St. Augustine grass is stressed or not thriving — perhaps due to drought, disease, or improper mowing — crabgrass can quickly take over.

The impact of crabgrass on St. Augustine’s lawns can be significant. The aggressive nature of crabgrass allows it to outcompete St. Augustine grass for resources such as sunlight, water, and nutrients, resulting in thinning and patchy areas in the lawn. Besides being aesthetically unpleasing, these bare spots provide an ideal environment for more crabgrass and other weeds to establish, leading to a vicious cycle.

Crabgrass is especially problematic in St. Augustine lawns because of its ability to thrive in the same warm, sunny conditions that St. Augustine grass prefers. Moreover, some common herbicides used to control crabgrass can harm St. Augustine grass, making it challenging to manage an infestation without damaging the lawn.

Understanding crabgrass and its impact on St. Augustine lawns is crucial for effective lawn care. By recognizing the conditions that favor crabgrass and taking steps to promote the health of St. Augustine grass, homeowners can reduce the risk of a crabgrass invasion.

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What is crabgrass look like?

How To Kill Crabgrass in St Augustine Grass

  •   Thin, pointed leaves with a lighter green color.
  •   Grows in a prostrate manner, spreading out from a central point.
  •   It features unmistakable seed heads and finger-like projections that extend upward from the plant, usually visible in late summer.

Differences to St. Augustine Grass

  •  St. Augustine grass has broad, flat blades.
  •   It grows more upright compared to crabgrass.
  •   Rarely produces seed heads in a lawn setting.

Signs of a Crabgrass Infestation

  •   Patches of thinning St. Augustine grass due to competition for essential resources.
  •   Changes in your lawn’s texture and color due to the presence of crab grass.
  •   Large, unsightly patches in your lawn if left untreated.

How to get rid of crabgrass in St Augustine

Crabgrass can be particularly stubborn in St. Augustine grass, but don’t worry; several practical strategies can help you regain control of your lawn. These strategies to kill crabgrass in St Augustine include preventive measures, organic solutions, and carefully selected chemical treatments.

1. Preventive Measures:

   Healthy lawn practices are the first line of defense. Regular mowing at the correct height and watering deeply but infrequently can discourage crab grass growth.

   Overseeding thin areas in the fall and applying slow-release nitrogen fertilizer in late spring can help your St. Augustine grass outcompete crabgrass.

2. Organic Solutions:

   If you prefer an organic approach, Corn Gluten Meal is a natural pre-emergent herbicide that prevents crabgrass seeds from germinating.

   Good old-fashioned hand pulling can be surprisingly effective for a more minor infestation. Just make sure to pull out the entire plant, including the roots!

3. Chemical Treatments:

Here’s where things get a bit technical. Several products on the market are designed specifically for killing crabgrass in St Augustine. For instance, AgraLawn Crabgrass Killer is a extreme crabgrass killer known for tackling stubborn crabgrass without harming your lawn.

Solitaire Crabgrass Killer is another excellent option. It’s a post-emergent herbicide, which means it targets crabgrass after it has sprouted. This makes it perfect for tackling an existing infestation.

Scotts Step 1 Crabgrass Preventer, Greenyard Crabgrass Preventer, Trimec Crabgrass Plus, and Zamzows Defendz Crabgrass Preventer are all pre-emergent products. They work by preventing crabgrass seeds from germinating, making them an excellent preventive measure to apply early in the season.

It’s essential to understand the difference and use the correct product depending on the stage of the crabgrass in your lawn. For prevention, use a pre-emergent in early spring before the crabgrass seeds germinate. If crabgrass has already appeared on your lawn, use a post-emergent treatment to kill it. Always read the product label for specific application instructions and to ensure it’s safe for use with St. Augustine grass.

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Maintaining a Crabgrass-Free St. Augustine Lawn

Crabgrass can be an unwelcome guest in your St. Augustine lawn, but several effective long-term strategies can help prevent the re-infestation of this pesky weed.

1. Regular Aerating and Topdressing

Compacted soil is a favorite environment for crabgrass. Regularly aerating your lawn can help keep the soil loose and less hospitable to crabgrass. Following aeration, topdressing with a thin layer of organic matter can aid in maintaining healthy soil structure.

2. Proper Disposal of Weeded Plants

When you’ve removed crabgrass from your lawn, ensure you dispose of it properly. Placing it in a sealed trash bag will prevent seeds or plant parts from re-rooting or germinating elsewhere.

3. Use of Nonselective Herbicides

Nonselective herbicides like Glyphosate can be a cost-effective solution in areas heavily infested with crabgrass. It’s important to note that these herbicides will also kill other plants they come into contact with, so they should be used judiciously.

4. Mowing and Cleaning Practices

After mowing a crabgrass-infested lawn, rinse your mower thoroughly. This prevents the transfer of crabgrass seeds to uninfested areas. Maintaining a higher mowing height can help your St. Augustine grass outcompete crabgrass.

5. Preventive Measures

Preventing seed production is crucial in a successful crabgrass management program. Pre-emergent herbicides can stop crabgrass seeds from germinating, and products like Rural King Crabgrass Preventer, Scotts Step 1 Crabgrass Preventer, IFA Crabgrass Preventer, Menards Crabgrass Preventer, Greenyard Crabgrass Preventer, Green Thumb Crabgrass Preventer, and Zamzows Defendz Crabgrass Preventer can be applied early in the season for this purpose.

Remember, the best defense against crabgrass is a healthy, well-maintained lawn. Implementing these strategies can effectively prevent crabgrass re-infestation in your St. Augustine lawn.

Does baking soda kill crabgrass?

Yes, baking soda kills crabgrass as it is phytotoxic and desiccates the plant. However, baking soda is nonspecific and can harm other plants it comes into contact with. Therefore, careful application is needed to prevent damage to the rest of your lawn.

Final Thoughts

Getting rid of crabgrass in St. Augustine lawns is challenging but achievable. In essence, the successful control of crabgrass in St. Augustine lawns hinges on early detection, timely intervention, and consistent management. With the right tools and techniques, homeowners can reclaim their lawns from this invasive weed.

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