How to control weeds in a St. Augustine grass lawn

St. Augustine grass is arguably the most popular lawn grass among homeowners. That is because it can tolerate high heat or temperatures of up to 100 degrees F, soil salinity, and humidity.

But perhaps its most significant selling point is that it makes an excellent dense turf or lawn and is less vulnerable to weeds.

However, some pesky weeds can pop up in St. Augustine grass and make your lawn look unsightly, prompting you to find a solution to control them.

So, how do you kill weeds without killing St. Augustine grass?

Controlling weeds in a St. Augustine grass lawn requires a lot of thought. However, you can use the traditional methods of mowing, hand pulling, fertilizing, or herbicides.

Essentially, choose a method based on the type of weeds in your area. That will tell you the best treatment to apply and how to time it.

For example, if you go for pre-emergent weed control, the chemical you buy should not kill St. Augustine grass but only target the weed.

How to control weeds in a St. Augustine grass lawn

Controlling weeds in a St. Augustine grass lawn does not have to be challenging.

Here are some methods to kill winter weeds in St. Augustine grass without destroying them.

1. Remove weeds from St. Augustine grass by hand

Hand-pulling weeds or hand-weeding is whereby you pull one weed at a time by hand.

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The method is cumbersome because it requires you to cover the entire area of your lawn and do it by hand.

But the advantage is that it can prevent any annual or perennial weeds from invading your lawn.

Besides, it is the best method for controlling the most problematic weeds without killing St. Augustine grass.

St Augustine grass lawn
Image by: Flickr/Claudia

Hand-pulling is more effective if you do it regularly or immediately see a weed cropping up in your St. Augustine grass lawn.

Also, use the method when the weeds are young before setting seeds. For long-term results, consider removing the entire weed, including the rhizome, roots, tubers, and bulbs.

If a weed with a thick taproot has invaded your lawn, use a wide-bladed screwdriver or dandelion fork to remove it.

2. Mowing

Mowing St. Augustine grass is crucial to keeping the lawn tidy and preventing the growth of weeds. However, understand that mowing does not kill them.

Instead, regular mowing ensures the weeds do not set seed. If they set seed, sprouting will occur each time you mow, and it becomes more challenging to eliminate the unwanted plants.

Make sure to mow your St. Augustine grass lawn at least weekly to control weeds.

For the best results, the grass must have reached a height of between three and four inches.

Adjust the cutting length to about a third of the leaf blade if mowing causes too much stress on St. Augustine grass.

3. Apply post-emergent herbicide

You can get rid of broadleaf weeds in a St. Augustine grass lawn by applying a post-emergent herbicide.

A post-emergent treatment involves using herbicide on weeds that have already grown.

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But the method is different when controlling weeds in St. Augustine grass lawn. That is because the grass is sensitive to specific chemicals found in common herbicides.

Avoid using herbicides containing 2,4-D, MSMA, MCPP, and dicamba as the active ingredient. Although these chemicals kill weeds, they destroy St. Augustine grass.

Instead, the best herbicide should contain Atrazine as the active ingredient since it will eliminate weeds without damaging your lawn.

How to keep weeds from growing in St. Augustine grass

You can prevent weeds from growing in St. Augustine grass lawn by doing the following:

1. Water your grass lawn

Watering St. Augustine grass helps keep your lawn healthy and maintains its thickness.

When St. Augustine grass is thick, it chokes out weeds and prevents them from growing.

Ensure to wet the soil to a depth of at least six inches.

2. Fertilize your lawn

St Augustine grass lawn
Image by: Flickr/Justtjenny

Fertilizing St. Augustine grass helps ensure it gets enough nutrients to grow. But it can also supply weeds with the same nutrients.

The only difference is that it contributes to the thickness of the St. Augustine lawn. So the weeds must find a space to grow when the grass gets dense above the soil surface and root zone.

But they will not get enough sunlight to grow without space. Eventually, they will die off, leaving the grass to grow.

3. Apply pre-emergent herbicide

A pre-emergent herbicide helps prevent weeds before emerging from the soil surface. Applying the herbicide will keep the weeds from growing in a St. Augustine grass lawn.

If you encounter a lot of crabgrass, a pre-emergent herbicide will prevent the weeds from growing in the summer and spring.

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What causes weeds in St. Augustine grass?

Like any other plant, weeds need enough water, sunlight, and nutrients to grow.

Therefore, when you water your lawn or apply fertilizer, weeds will have the necessary elements for growth and thus become part of the lawn.

Also, weeds will grow when you fail to water or fertilize your St. Augustine grass lawn. That is because the grass will not grow thick enough to choke out the weeds and compete for space against your good grass.

What are the common weeds in St. Augustine grass?

Different weeds can infest St. Augustine, including broadleaf, sedges, and grass weeds. The weeds that grow will depend on your area.

However, the most common weeds in St. Augustine grass include clover, chickweed, henbit, dollar weed, crabgrass, bermudagrass, and guinea grass.

Bottom line

St. Augustine grass can grow healthy and thick if you control weeds. You can use different methods to kill weeds on St. Augustine without destroying the grass.

First, you can mow the grass to prevent weeds from setting seed. Alternatively, you can hand-pull weeds from your St. Augustine grass lawn to eliminate them from the root without destroying the grass.

Next, consider fertilizing or applying pre-emergent herbicide to keep weeds from growing in St. Augustine.

Another option is to water the lawn to keep St. Augustine grass thick and choke the weeds, preventing their continued growth.