Why is My St Augustine Grass Turning Light Green?

St. Augustine grass is a favorite of warm weather homeowners everywhere! It grows gloriously green in even the hottest weather. However, even St. Augustine grass can sometimes look less than healthy.

What causes St. Augustine grass to turn light green? What is the solution? Let’s figure out how to get your yard looking healthy again!

About St. Augustine grass

St. Augustine grass is popular in Florida and the gulf area. It grows well in warm, humid environments. Since St. Augustine grass is salt tolerant, it does well near the ocean, as well. This hardy grass doesn’t need much water and grows into a dense mat with blue-ish green blades.

What makes St. Augustine grass turn light green?

Just because St. Augustine grass is tough and hardy doesn’t mean that it will never have any problems! If you have noticed light green blades or patches in your lawn, it could be due to one of the following reasons.

Take All Root Rot

The pathogen for Take All Root Rot is always present in the roots of the grass, no matter how healthy it is! Release of the pathogen occurs when the grass and surrounding ground get too wet or the grass is stressed for some reason.

The first sign of Take All Root Rot is patches of yellow or light green grass. Eventually, the roots turn white with black spots. Then, the grass will thin as the disease spreads.


Help reduce the stress on your St. Augustine grass by only mowing one-third or less of the total grass blade height each time you mow. A fertilizer with equal parts of nitrogen and potassium may also help your grass regain its health.

You may try a fungicide, but they are usually more effective when the disease is still in the roots of the plant. If you have had issues with Take All Root Rot in the past, you may want to consider a fungicide, such as Scott’s DiseaseEx, to prevent future fungal outbreaks.


Pesky nematodes can attack the grass at the roots. This leads to thin, pale grass. If you suspect nematodes are the culprit for your light green grass, take a soil sample to your local extension office to be tested.


Unfortunately, there is not a one-size-fits-all chemical cure for nematodes. Your best defense against these pests is to ensure that your grass and soil are as healthy as possible. Keep grass blades at least 3-4 inches tall. Make sure your soil has sufficient potassium levels to support healthy grass.

Lack of nutrients

St. Augustine grass requires nitrogen and iron to maintain its rich, green color. Sandy soil may drain these necessary nutrients through the soil quickly.


A nitrogen-rich, slow-release fertilizer may give your grass a needed boost to regain its green color. If you suspect your grass needs a dose of iron, try a liquid iron (also known as ferrous sulfate) treatment.

It may be helpful to test the soil’s iron levels before treatment so you know how much iron to add. Mix 2 ounces of liquid iron with 3-5 gallons of water per 1,000 square feet of lawn.

Too much shade


St. Augustine grass thrives in the sunshine! Too much shade makes for unhappy St. Augustine grass.


If your St. Augustine grass is struggling in the shade, consider trimming back the trees and bushes that block the sun. You could also overseed the shaded area with a variety of more shade-tolerant grass, like ryegrass.

Easy steps for greener St. Augustine grass!

Slow-release fertilizer

A slow-release fertilizer that has a rich balance of nitrogen, phosphorus, and potassium will feed your St. Augustine grass well for up to eight weeks. Not only do slow-release fertilizers save your time, but they also help the grass get nutrients gradually.

Lots of sun

Your St. Augustine grass will grow well in a sunny yard! If your lawn is mostly shade, consider a different variety of grass seed or a grass seed blend.

The right amount of water

St. Augustine grass has the ability to thrive on very little water. It only needs about ¾ of an inch of water twice a week. You may need to increase this amount if you have sandy soil or a particularly hot week.

Frequently Asked Questions

How to make St. Augustine grass dark green?

Often, a nitrogen-rich fertilizer is the key to dark green St. Augustine grass. Nitrogen helps the grass create chlorophyll. Chlorophyll is what gives grass and plants their green color.

Are coffee grounds good for St. Augustine grass?

Are coffee grounds good for St. Augustine grass

You may have heard that grass appreciates a good cup of coffee just as much as we do! It is not the caffeine that the grass craves but the nitrogen, phosphorus, and other minerals in the coffee grounds.

Coffee grounds act as a slow-release fertilizer for your grass. This means the nutrients break down slowly, allowing the ground and lawn to absorb them over a long period of time.

Should I use Ironite for St. Augustine grass?

Ironite is a granulated mineral iron supplement for grass. Often, light green St. Augustine grass is caused by a lack of iron in the soil. An iron solution can be applied to St. Augustine grass up to four times a year to balance the iron in the lawn and create that beautiful, green grass you desire!

Take a soil sample to your local extension office. They can test it for iron levels and let you know just how much iron to apply to your lawn.

Final Thoughts

There are a variety of reasons for lime green St Augustine grass. It is best to diagnose the problem before you treat it. Whether you have fungus, pests, or just a lack of nutrients, you can heal your grass and have a bright green lawn once again!