Weed Control For St. Augustine Grass

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Weed Control for St. Augustine Grass

Want to learn how to control the most troublesome weeds found in your St. Augustine grass? Read on to learn about the tips and tricks to eliminate the weeds prone to invading your lawn.

St. Augustine grass is a warm-season grass that thrives in most soil types and can typically withstand heat, shade, humidity, and salt.

You will need to work diligently to keep it looking fresh, green, and healthy. The best way to do it is by controlling the growth of weeds and keeping the grass in great shape.

This can be achieved by sticking to a yearly maintenance schedule and by knowing and treating the weeds commonly found in St. Augustine grass.

Common Weeds Found in St. Augustine Grass

You will find both broadleaf and grassy weeds growing in your St. Augustine grass.

Broadleaf weeds are easy to spot because they do not look like grass.  This makes them stand out.

Grassy weeds are harder to spot because they are actually grass seeds that have sprouted and grown as a single leaf.

Below is a list of the most common types of each broadleaf and grassy weeds typically found in St. Augustine turfgrass.

  • Broadleaf: chickweed, henbit, clover, and dollar weed
  • Grassy weeds: goosegrass, crabgrass, annual bluegrass or poa annua, dallisgrass, and bermudagrass

Henbit, chickweed, and clover are also cool-season weeds, so be on the lookout for these weeds right now, during the fall season.

St. Augustine Grass Yearly Weed Maintenance Tips

January through April 


To control the annual weeds like crabgrass, goosegrass, and other weeds, apply a pre-emergent herbicide early in the year.

The application times for the coastal and central areas are mid-February, and for piedmont or mountain areas, it will be mid-march.

In Texas, these times can vary greatly because of differing soil-warming temperatures.

You can also apply a post-emergent herbicide to control the existing winter weeds.

Avoid using it on your lawn when the turf is starting to become green.

If the weed issue starts and the grass grows green with a warmer temperature, wait until the grass is fully green before applying the post-emergent herbicide.

Meanwhile, mow and bag the weeds.

St. Augustine grass is sensitive to some herbicides like 2,4-D. Follow the manufacturer’s directions when using this herbicide and apply with caution.

May Through August

Some selective pre-emergent herbicides are specifically labeled to use on St. Augustine grass and should be applied in spring to prevent the weeds from growing that summer.

If you do not apply a pre-emergent herbicide in spring, the weeds will grow and will need to be controlled with post-emergent herbicides.

September through December

Pre-emergent herbicides need to be applied twice a year. One of those applications should be done in the fall season to combat the growth of winter weeds.


Maintenance Tips for St. Augustine Grass Lawns 


The most preferred height of mowing St. Augustine grass is usually 2.5 – 3 inches.

If you decide to keep your grass shorter, you will need to mow more often.  Generally, every 5 days during spring and summer.

Mowing regularly throughout the growing season using sharp blades and not removing more than one-third of the grass height is the best way to get the healthiest turf.


The season and weather will determine how much water your grass needs.

During the cold season, it will require a small amount of water. But during the hot season, it might require water three to four times each week.

dry lawnThe grass will show signs if it is stressed from drought.

If folding, wilting, and footprints are staying after a walk on the lawn, it needs irrigation.

Be careful not to overwater because it will attract insects and diseases.


St. Augustine grass prefers a nitrogen-rich fertilizer.

Follow instructions exactly when applying because over-fertilization invites insects and diseases to invade. Too much fertilizer can also cause a thatch build-up.

Fertilizing in late fall will help your grass stay green longer, as well as foster faster re-growth in spring.

You should be applying fertilizer every 30-60 days starting in early spring and continuing through late fall.

Pre-Emergent Herbicides

Pre-emergent weed killers can prevent grassy and broadleaf weeds before they appear, but will not work on already developed growth.

Before you apply weed killer on your St. Augustine grass, make sure the grass isn’t stressed from drought, and add water if needed.

In the spring, add pre-emergent weed killers when the temperatures have reached above 65 degrees Fahrenheit for a few consecutive days.

In the fall, use it when the temperatures have been between 55 to 60 degrees Fahrenheit for about four days in a row.

You can find pre-emergent herbicides in liquid and granular forms.

If you use a granular type, make sure you activate it as soon as possible by watering St. Augustine with .5 inches of water.

Post-Emergent Herbicides

Some post-emergent products contain several herbicides, and St. Augustine is sensitive to some chemicals.

So, again, read the labels carefully to ensure they are safe to use, won’t damage the sod, and only target unwanted weeds.

Before applying it, make sure the grass is watered and not suffering from drought, and no rain in the forecast for 24 hours after application.

The herbicide needs time to make contact with weed surfaces and begin to work.

Avoid mowing immediately before or after application.

A good rule of thumb is to use post-emergent herbicides only when soil temperatures are above 55 degrees Fahrenheit.

Do not apply on windy days, as it can blow and damage nearby plants.

Final Thoughts

Many North Texans choose St. Augustine grass because it stays green in both hot and dry conditions.

Remember though, when it comes to weeds, you must treat them very early on, when they are still small.

You need to be able to see the weeds on your lawn and your lawn needs to be green and actively growing when using herbicides.

St. Augustine grass is sensitive to many chemicals, so contacting a professional to help with weed control will make maintaining a lush, green lawn an easy and stress-free process for you.


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M Valdivia

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