Will St. Augustine Grass Choke Out Weeds?

As a longtime gardening enthusiast, I know the sight of weeds invading a lawn all too well. After spending hours sweating in the summer heat to nurture a lush, green lawn, it can be incredibly frustrating when uninvited guests like dandelions, crabgrass, and clover creep in. Believe me, I’ve waged my own share of wars against weed invasions over the years.

But what if your grass could do some of the weed-fighting work for you? Enter St. Augustine grass. As I’ve learned firsthand, St. Augustine is a warm season turfgrass with traits that make it a powerful natural weed deterrent.

In this article, I’ll share how the vigorous growth habit of St. Augustine allows it to choke out many common weed varieties. You’ll discover which weeds St. Augustine particularly dominates along with management tips to maximize its weed-fighting prowess. We’ll also discuss certain stubborn weeds that can still sometimes challenge St. Augustine’s defenses.

If you’re tired of spot-treating weeds or using harsh chemicals on your lawn, growing thick St. Augustine turf may be the organic solution you’re looking for. I’ll share the weed-control tricks I’ve picked up through years of experience establishing lush, weed-free St. Augustine lawns. Let’s get growing!

How Does St. Augustine Grass Beat Weeds?

As a longtime gardening enthusiast, I’ve spent years testing different methods and grass types to keep weeds at bay in my lawn. In my experience, St. Augustine grass emerges as one of the best organic defenses against weed invaders thanks to its vigorous growth habits.

St. Augustine forms such a dense, thick turf that it simply crowds out space for weeds to take hold when properly established and cared for. Below, I’ll share more about the traits that make St. Augustine a lawn warrior against weeds.

Why St. Augustine Grass is Ideal for Weed Prevention

There are a few key reasons why St. Augustine excels at deterring weeds naturally:

  • Fast lateral growth – St. Augustine rapidly produces above ground stolons that spread horizontally and form a dense mat. This thick carpet of grass quickly steals the light, moisture and space that weeds need.
  • Thatch buildup – In mature St. Augustine lawns, layers of accumulated organic matter and stolons create a thatch barrier. This further obstructs weeds from penetrating down to the soil and germinating.
  • Deep root system – The extensive root network of St. Augustine soaks up available water and nutrients. This starves out shallow-rooted weeds.
  • Choking action – St. Augustine’s propensity to grow up and over objects, including weeds, literally chokes them out. Its rapid vertical growth shades and smothers weed seedlings.

In summary, St. Augustine forms such an impenetrable turf canopy that it’s difficult for weed invaders to establish a foothold. But proper lawn care is key to maximizing its weed-fighting power.

Tips to Maximize the Weed Choking Ability of St. Augustine Grass

Pulling weeds from St. Augustine Grass

To fully unlock the weed-blocking prowess of St. Augustine grass, I recommend:

  • Regular mowing at 3-4 inches – This encourages the lawn to grow thick and develop extensive stolon systems. But never scalp below 2 inches.
  • Watering early morning – Allow the lawn to dry slightly between waterings while still meeting its thirst. This discourages weeds more prone to overwatering.
  • Annual core aeration – Relieve soil compaction that restricts deep St. Augustine root growth.
  • Overseeding thin areas – Patchy sections are prime real estate for weeds. Fill them in promptly with new sprigs.
  • Selective pre-emergent herbicide – Use at the beginning of weed season to form a barrier that deters germination of seeds.

With attentive maintenance that caters to the preferences of St. Augustine, you can leverage its natural weed-blocking talents all season long.

While no grass can prevent weeds completely, St. Augustine’s dense carpet-like growth habit enables it to naturally choke out many common weed problems. Next, we’ll discuss specific intruders that meet their match against St. Augustine.

Common Weeds That St. Augustine Grass Can Deter

In my experience battling weeds for years, St. Augustine grass reliably chokes out some of the most notorious warm season lawn invaders. The dense carpet of grass it forms simply crowds out these common intruders.

Below I’ll share the specific weeds that St. Augustine excels at shading out and smothering through its aggressive growth habits.

Crabgrass and Goosegrass

Two of the most loathed summer weeds are crabgrass and the similar goosegrass. These annual grasses explode once soil temperatures rise, spreading rapidly through seed heads.

While difficult to control in thin lawns, crabgrass and goosegrass struggle to establish in dense St. Augustine turf. The extensive root systemabsorbs water and nutrients first, starving crabgrass roots. Meanwhile, St Augustine’s propensity to grow up and over objects physically smothers crabgrass seedlings.

Maintaining proper mowing height and fertilization further allows St. Augustine to shade out these low-growing annual weeds. Its fast-spreading stolons simply dominate the lawn, leaving little room for crabgrass or goosegrass roots to take hold.

Dandelions, Clover and Wild Violets

St. Augustine also naturally deters broadleaf weeds like dandelions, clover and wild violets through its thick turf canopy.

The horizontal stolons of St. Augustine grow to completely cover bare spots that weeds would otherwise invade. Over time, the accumulating thatch layer also helps block these weeds. Meanwhile, St Augustine’s vertical growth and dense shade prevents just enough sunlight from reaching the soil to inhibit weed seed germination.

While small weed outbreaks may occasionally occur, established St. Augustine should choke out most broadleaf weeds within one growing season. Timely pre-emergent herbicide paired with attentive lawn care further bolsters its defenses.

Nutsedge and Other Sedge Weeds

Lastly, St. Augustine excels at controlling tricky perennial sedges like nutsedge. The extensive root system of St. Augustine soaks up water and nutrients aggressively, starving out shallow sedges.

St. Augustine also grows so thickly it eventually crowds out space for new nutsedge shoots to emerge. And its propensity to intertwine with and grow over other plants allows St. Augustine to literally smother out clumps of sedge weeds.

So while nutsedge can challenge other warm season grasses, St. Augustine often conquers this stubborn perennial through its vigorous growth habit alone.

While no lawn can prevent all weeds, St. Augustine provides a line of defense well-suited to choking out some of the most common annual and perennial invaders through organic means.

Problems Choking Out Weeds in St. Augustine Grass

While St. Augustine excels at deterring many common weeds, it isn’t impervious to all invaders. Certain problematic weeds can still sometimes breakthrough and challenge even the thickest St. Augustine lawn.

As a seasoned gardener, I’ve discovered a few factors that can hinder the weed-blocking prowess of St. Augustine grass. Here are the main problems to watch for.

Avoiding Thinned Out Sections in St. Augustine Turf

The vigorous growth habit of St. Augustine forms a weed-suppressing barrier, but only when it’s grown densely. Sections that thin out provide prime real estate for weeds to take root.

St. Augustine may spread more slowly if mowed too short or deprived of adequate nitrogen. Drought conditions can also cause dieback. These stressed areas leave gaps in the lush turf that weeds will quickly fill.

To maximize the weed-choking density of St. Augustine, proper mowing, fertilizing and irrigation are key. Be diligent about reseeding bare patches to keep its defenses strong.

Certain Stubborn Weed Species Persist

While St. Augustine handles most summer annual weeds well, a few stubborn perennials can still sometimes break through and persist long-term if left unchecked:

  • Yellow nutsedge – This perennial sedge has an extensive underground tuber system that helps it survive amongst thick grasses.
  • Wild garlic and onion – These early emerging weeds establish before St. Augustine breaks dormancy in spring. Their strong scents also deter grazing by insects.
  • Virginia buttonweed – Adaptations like seed pods that cling to shoes or mowers allow its spread. St. Augustine alone doesn’t provide full control.

These aggressive weeds often require targeted spot sprays for full removal even in robust St. Augustine turf. So don’t rely solely on the grass to deter them.

Herbicides Are Still Necessary in St. Augustine Lawns

While St. Augustine provides organic weed suppression, some chemical control is still advisable for best results:

  • Pre-emergent herbicides in spring prevent many weeds from even sprouting, complementing the choking effect of the thick grass.
  • Early intervention with post-emergent sprays keeps invaders from growing out of hand if they sneak through.
  • Spot treatments target stubborn weeds like sedges and Virginia buttonweed that resist the grass alone.

In summary, St. Augustine forms an effective first line of defense against weeds. But strategically timed herbicide applications provide that extra layer of protection to keep the lawn weed free.

Thick, vigorous St. Augustine turf will deter most weeds. But a sharp eye and integrated weed control plan incorporating chemicals controls the few that persist. Maintaining dense grass growth is still the foundation for success.

FAQ: St. Augustine Grass and Weed Control

Over the years helping homeowners cultivate lush, weed-free lawns, I’ve fielded plenty of questions about maximizing St. Augustine’s natural weed-blocking abilities. Here I’ll answer some of the most common FAQs.

What Type of St. Augustine Grass Variety Resists Weeds the Best?

There are a few factors that determine how well a St. Augustine cultivar suppresses weeds:

  • Growth rate – Faster spreading varieties like Raleigh or Floratam quickly form a dense mat to block weeds. Slower growers may take longer to choke out weeds.
  • Texture – Finer-bladed types like Floratam develop dense shade. Wider blades allow more sunlight to penetrate to potentially reach weeds.
  • Thatch production – Varieties prone to thatch accumulation like Palmetto enhance the physical weed barrier. Less thatchy types can’t block as readily.

While all St. Augustine resists weeds, fast-growing, finer-bladed cultivars that accumulate thatch may provide the most vigorous chokehold on invaders.

How Long Does it Take for St. Augustine to Choke Out Existing Weeds?

If dealing with a severe weed infestation, it may take St. Augustine up to a full growing season to fully reclaim the lawn:

  • 60-90 days to establish initial thick coverage and begin shading and crowding out existing weeds.
  • Ongoing horizontal stolon spread to close gaps throughout the season, further blocking weed growth.
  • Eventual thatch accumulation (1-3 seasons) for maturing lawns enhances the physical weed barrier.

But strategic use of early post-emergent and pre-emergent herbicides accelerates results. And proper mowing, fertilizing and irrigation helps the grass maximize its natural weed defenses sooner.

Should Pre-Emergent Herbicide Be Used With St. Augustine Grass?

Absolutely, a pre-emergent herbicide is a great complement to St. Augustine’s organic weed suppression. An early spring application helps prevent summer annual weeds like crabgrass from even sprouting.

Pre-emergents create a chemical barrier that disables weed seeds as they germinate. This reinforces the physical barrier formed by dense St. Augustine turf, enhancing control.

Choose a St. Augustine-safe pre-emergent like prodiamine. Coordinate application timing with green-up and soil temperatures to fully leverage its preventative effects.

In summary, pre-emergent herbicide provides added insurance against breakthrough weeds invading thick St. Augustine turf. But the grass alone can still effectively deter many weeds when properly established and maintained.


As any gardener knows, fighting a constant battle against weed invaders in your lawn can feel never-ending. After years of trial and error caring for lawns myself, I’ve come to appreciate the weed-blocking power of St. Augustine grass.

When properly established and maintained, St. Augustine’s dense carpet-like growth habit provides effective natural suppression against many notorious summer weeds. Crabgrass, dandelions, and even stubborn sedges struggle to take root amid vigorously growing St. Augustine turf.

But remember, thinning turf and insufficient care create openings for weeds to sneak through. Integrating selective herbicide applications with the organic barrier formed by St. Augustine gives the best control.

Overall, I highly recommend St. Augustine grass for homeowners seeking a lush, thriving lawn that minimizes weed headaches naturally. Follow the tips I’ve shared to maximize its formidable chokehold on invaders. With a little patience and attentive care, you’ll be well on your way to a weed free oasis.

As your resident lawn care nut, I’m always happy to answer additional questions about organically blocking weeds while growing thriving St. Augustine turf. Don’t hesitate to reach out! Let’s keep our lawns lush and weed free together.

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