Weeds In St Augustine Grass

Seeing weeds in St Augustine grass can be frustrating. You work hard on your lawn, and these invaders seem to pop up overnight. The good news is that with the right approach, you can get your turf back on track. This guide will walk you through effective control strategies, from identification to treatment and prevention.

St. Augustine is a popular warm-season grass, prized for its thick, carpet-like growth. However, its very density can sometimes create challenges. Shade, poor soil, or incorrect watering can create thin spots. Weeds quickly exploit these weak areas, competing for water, nutrients, and sunlight.

Identifying Common Lawn Invaders

Knowing your enemy is the first step. Here are the most common weeds you’ll find:

Broadleaf Weeds: These have wide, flat leaves. Examples include dandelion, clover, and dollarweed. They are often easier to spot and target with selective herbicides.
Grassy Weeds: These look like grass but grow faster and taller. Crabgrass, dallisgrass, and goosegrass are common culprits. They can be trickyer to control because they blend in.
Sedges: Often mistaken for grass, sedges have triangular stems (“sedges have edges”). Nutsedge, with its yellow or purple flower heads, is a frequent problem in damp soil.

Why Weeds Appear in Your Lawn

Weeds are symptoms of an underlying issue. Simply killing the weed won’t stop new ones if the condition remains. Common causes include:

Mowing Too Short: St. Augustine should be mowed at 3.5 to 4 inches. Short mowing weakens the grass and lets sunlight reach weed seeds.
Improper Watering: Frequent, shallow watering encourages shallow grass roots and weeds like nutsedge. Deep, infrequent watering is better.
Soil Compaction: Hard soil prevents air, water, and nutrients from reaching grass roots. This stresses the St. Augustine.
Nutrient Deficiency: An underfed lawn is a weak lawn. A soil test can tell you exactly what your grass needs.

Effective Control Strategies: A Step-by-Step Plan

A healthy lawn is your best defense. Follow this integrated plan for effective control.

Step 1: Cultural Practices for a Strong Lawn

Start with these foundational steps. They cost little but make a huge difference.

Mow High: Keep your mower blade sharp and set to 3.5-4 inches. Never remove more than one-third of the grass blade at a time.
Water Deeply: Water only when needed, providing about 1 inch of water per session. This encourages deep root growth. Early morning is the best time.
Fertilize Smartly: Use a slow-release fertilizer formulated for St. Augustine. Follow the schedule for your region, typically in late spring and early fall.
Aerate Annually: Core aeration relieves soil compaction. It allows water, air, and fertilizer to reach the root zone effectively.

Step 2: Manual Weed Removal

For isolated weeds, pulling them by hand is a safe and immediate solution. Ensure you get the entire root system, especially with tap-rooted weeds like dandelions. A weeding tool can be very helpful. This is most effective when the soil is moist.

Step 3: Using Herbicides Correctly

When weeds are widespread, herbicides may be necessary. It’s crucial to choose the right type.

Pre-emergent Herbicides: These prevent weed seeds from sprouting. Apply in early spring before soil temperatures reach 55°F for summer weeds, and in fall for winter weeds. They do not kill existing weeds.
Post-emergent Herbicides: These kill weeds that are already visible. Always choose a product labeled as safe for St. Augustine grass.
- For broadleaf weeds, look for herbicides containing 2,4-D, dicamba, or MCPP.
- For grassy weeds, products with sethoxydim (e.g., Poast) are often safe for St. Augustine.
- For nutsedge, use a herbicide labeled specifically for sedges, like halosulfuron or imazaquin.

Critical Tip: Always read and follow the label instructions exactly. Applying herbicide during stress (drought, extreme heat) or at the wrong rate can damage your St. Augustine. On hot days, its better to apply in the cooler evening hours.

Step 4: Addressing Bare Spots

After removing weeds, you’ll often have a bare patch. Weeds will return if you don’t fill it with grass. You can use St. Augustine plugs or sod to repair these areas quickly. Keep the new area consistently moist until it establishes.

Seasonal Weed Control Calendar

Late Winter / Early Spring: Apply pre-emergent herbicide. Begin mowing as grass greens up.
Late Spring: Apply post-emergent herbicide for early summer weeds. Apply first round of fertilizer.
Summer: Spot-treat weeds as they appear. Maintain proper mowing and watering. Avoid herbicide applications during extreme heat.
Early Fall: Apply pre-emergent for winter weeds (like henbit). Apply fall fertilizer to strengthen roots.
Late Fall / Winter: Lawn is dormant. This is a good time to plan for next year and service equipment.

FAQ: Your Weed Control Questions Answered

Q: What kills weeds but not St. Augustine grass?
A: Selective herbicides labeled specifically for use on St. Augustine lawns. The label will list the weeds it controls and state it is safe for your grass. Using a non-selective herbicide like glyphosate will kill everything.

Q: How do I get rid of crabgrass in St. Augustine?
A: Use a post-emergent herbicide with sethoxydim, which targets grassy weeds but spares St. Augustine. For prevention, apply a pre-emergent in early spring before crabgrass seeds germinate.

Q: Is vinegar safe to kill weeds in my lawn?
A: Household vinegar is a non-selective weed killer. It will burn the foliage of any plant it touches, including your grass. It’s not recommended for spot treatment in lawns because it can damage the St. Augustine and doesn’t kill the root.

Q: Why do I have so many weeds in my healthy-looking lawn?
A> Even healthy lawns can have weeds. Seeds blow in from neighbors, birds, or are tracked in. Regular pre-emergent applications and prompt spot-treatment of any escapes are key to keeping them at bay.

Q: Can I just spread more grass seed to choke out weeds?
A: St. Augustine grass is typically established from sod or plugs, not seed. The best way to “choke out” weeds is to promote thick, healthy turf through the cultural practices outlined above. A dense lawn leaves no room for weeds to establish.

Controlling weeds in St Augustine grass is an ongoing process, not a one-time event. By combining strong lawn care habits with timely treatments, you can maintain a beautiful, resilient lawn that leaves little room for unwanted guests. Consistency is your greatest tool in this effort.