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Why Is My St Augustine Grass Turning Yellow? 5 Reasons and Their Solutions!

St. Augustine grass is a gorgeous kind of green grass that adds immense beauty to your lawn. The grass is dark green in color and is mesmerizing to look at.

If we’re talking about the grass blades, they’re flat and broad. This gives them a distinct look.

The grass spread through stolons above ground. These are called runners.

The grass is native to the South-Eastern US, Texas, South America and Mexico. Many lawn keepers grow it because of its elegance.

However, sometimes you may be asking yourself the question, “Why is my St Augustine grass turning yellow?” We are here to answer just that!

Why Is My St Augustine Grass Turning Yellow
Yellowing in St Augustine- fungus or nutrient loss – via Reddit

Reasons For St Augustine Grass To Turn Yellow

If you begin seeing yellow spots on your grass, your lawn is probably suffering a disorder of some sort.

This can be due to a number of reasons.

1. Iron Chlorosis

If you’re seeing yellow streaks or yellow spots on the blades of the grass, your grass probably has Iron Chlorosis.

The disease happens when the soil is lacking in iron and is usually seen in the summer months because it is the growing season, and the grass can’t absorb iron very rapidly.

To fix this, you need to give your grass iron in some form. Iron sulfate and iron chelate work wonders in this department.

Chelated iron works better, but it is a little more expensive as compared to iron sulfate. Iron sulfate is also a solid alternative and poses no problems at all.

It adds iron directly to the soil and helps release the iron which is already present in the soil.

If you keep on adding iron supplements to your grass throughout the year, this problem will likely disappear.

Another way you can do this is by adding acid-forming fertilizer to the iron content once every 3 months. If you continue this practice throughout the year, the lawn will be perfectly fine.

2. Rains

If your St Augustine grass turns yellow in the time of spring usually, it is most probably because of heavy rainfall.

Rain extracts Nitrogen from the soil on which the grass is growing. The grass then starts turning yellow because of this lack of Nitrogen.

Sometimes rain can even cause waterlogged conditions in your lawn. This will prevent the St Augustine grass from absorbing essential nutrients necessary for its growth.

If you haven’t used any type of nitrogen fertilizer recently for your grass, try doing it soon. This will help in reviving the grass.

3. Yellow Circles On The Grass Is Due To Pests

Some fungi can attack the grass. A fungal infection can be identified if you spot yellow circles on the grass blades. These diseases are usually seen in one part of the lawn.

If your roots start rotting, it is most probably because of a fungal infection. This disease is triggered when you over-fertilize your soil, or there is a lot of rain happening in the area.

You will need to spray fungicide wherever you suspect infection. The best time when you can apply this fungicide is spring or fall.

You can mix½ ounce of azoxystrobin with 4 gallons of water and then spray this mixture onto a 1000 square foot lawn. This will work wonders for your grass.

You should apply this antifungal mixture to your lawn once a month. If you apply this with a gap of 28 days, you will need no other fungicides. Spray this on your lawn in fall and spring.

What causes yellow circles in grass
St Augustine Yellowing Continued – via Reddit

4. Your Grass Turning Yellow In The Summers.

Lawns with St. Augustine grass in them experience Chlorosis in the summer months. The lawn may be yellowing because of this disease. This arises due to a lack of Chlorophyll.

When the temperature is high, it prevents the grass from absorbing essential nutrients from the soil like iron and Nitrogen. A lack of these translates into this disease.

What you can do to solve this is add some organic matter to the grass to lower the pH of the grass. This will also increase the nutrient absorption of the grass. Try adding liquid seaweed and iron onto the grass.

5. Is Your St. Augustine Grass Turning Yellow After Fertilizing?

If you often ask yourself this question “Why is my St. Augustine grass turning yellow?” It is likely this reason.

If you have fertilized the soil recently and the grass turns yellow after that, it is a solid sign of over-fertilizing. If you add too much fertilizer to the grass, that can also be a problem.

Giving the grass excess nitrogen salts in the form of fertilizers will burn the grass blades. This phenomenon is called leaf scorch. The grass starts turning yellow at the bottom but turns brown at the top.

You are only likely to experience this if you use quick-release fertilizers. This is one of the reasons it is better to use slow-release fertilizers, something like Milogranite.

If you have noticed leaf scorch in the earlier phase, that’s good. You can water the lawn thoroughly and fix this. Watering the affected areas will wash away all of the unneeded salts that might be there in the grass.

6. Chinch Bugs

Chinch bug is one of the common pests that attacks St. Augustine grass. One sign of Chinch bugs is dead grass which is surrounded by a small circle of yellow grass. This is a sign of bug infestation.

If there is a thin layer of thatch in your lawn, the lawn is more vulnerable to a bug infestation. If you have thatch, it’s basically having dead organic material on your grass.

You can use a turf aerator to try and punch holes into the lawn. This will increase air movement in the lawn, which will help prevent a bug infestation.


If you keep asking yourself the question, “Why is my St Augustine grass turning yellow?” This article will have the answer to that question.

If you have additional questions, you can always reach out to us, and we’ll be happy to help.

Happy gardening!