why is my st augustine grass turning yellow

Why is My St Augustine Grass Turning Yellow? (5 Problems and Solutions!)

St.Augustine grass turns yellow mainly due to Iron Chlorosis. St.Augustine grass turns yellow in spring as the rain washes away Nitrogen in the soil. Yellow circles are seen on grass blades due to fungal infection. Fertilizer scorching also turns the St.Augustine grass yellow.

St.Augustine grass makes up for a beautiful lawn with dark green coloration. The grass blades are flat and broad. The grass spreads via aboveground stolons called runners.

It grows natively in the south-eastern US, Mexico, Texas, and Central and South America. It is loved by many lawn keepers for its elegance.

People that have St.Augustine lawns run into problems sometimes. They all mail me complaining that their lawn is yellowing.

St Augustine grass yellow streaks and spots

Do you see yellow spots on the blades of your St.Augustine grass? Your lawn is probably suffering from a disorder.

This is most likely due to Iron Chlorosis. You’ll see yellow-colored streaks and spots on the blades of St.Augustine.

This happens when the soil lacks Iron. This disorder is usually seen in the summer months as the grass couldn’t absorb iron as rapidly as it grows.

Iron supplement for St.Augustine grass

St.Augustine grass needs Iron to grow properly. St. Augustine grass can absorb Iron when it’s in the form of Iron Chelate and Iron sulfate.

Chelated iron works the best but it’s quite expensive. Iron sulfate is a good alternative as it works well for the purpose.

Iron sulfate

Iron sulfate not only directly adds Iron to the soil but also helps release the Iron already present in the soil as it’s acid-forming.

The best way to fix the Iron deficiency in your soil is by adding Iron sulfate/Iron supplements throughout the year. Adding it once off doesn’t give desired results.


Add acid-forming fertilizers with Iron content to the soil once every 2-3 months. Do this throughout the year and your lawn will be fine.

Milorganite works awesome. It is a slow-release fertilizer. If your lawn is of average size, you may use 5-10 bags of Milorganite for best results.

That is, you may want to use 50-100 pounds of Milorganite per 1000 sq. feet of the lawn.

St Augustine grass turning yellow in spring

Rains leech out the Nitrogen from the soil. The grass turns yellow due to the lack of Nitrogen. This is why St. Augustine grass turns yellow in spring.

Sometimes rains cause waterlogged conditions in your lawn. Waterlogged soil prevents the absorption of essential nutrients by St.Augustine grass.

If you didn’t apply any Nitrogen fertilizer recently, apply some in August. This helps revive the Nitrogen-deficient soil.

Note: If the yellow grass turns brown it is an indication of a fungal infection. Apply fungicide to treat the grass.

St Augustine grass yellow circles

A variety of fungi affect St.Augustine grass. A fungal infection is characterized by yellow circles on grass blades. Such diseases are usually seen only in a part of the lawn.

Take-all root rot is caused by a fungal infection. This disease is triggered by excess rain and overfertilizing.

You’ll need to spray a fungicide on the infected areas of the lawn. The best time to apply this fungicide is in the spring and fall.

Myclobutanil and Azoxystrobin work wonders on Take-all root rot. Mix 1/2 ounce of water in 4 gallons of water and apply this mixture on 1000 sq. ft of lawn.

Apply this fungicide mixture to your lawn on a windless day. Two applications 28 days apart would suffice. Spray in spring and fall.

St Augustine grass yellow in winter

St. Augustine grass will go dormant in winter when the soil temperature falls below 55 degrees. Dormant grass turns yellow.

The growth slows down as the temperature falls. St. Augustine grass turns partially green throughout the winter but might turn yellow in January.

How do I get St Augustine out of dormancy?

Give your St.Augustine lawn an inch of water every week and provide the required nutrients. Identify any pests in the lawn and eliminate them.

St Augustine grass turning yellow in summer

St.Augustine lawns experience Chlorosis in summer. The lawn may yellow because of this disorder which arises due to a lack of Chlorophyll.

High temperatures deter the grass from absorbing essential nutrients like Nitrogen and Iron which translates to Chlorosis.

You can add some organic matter to bring down pH and increase nutrient absorption by the grass. I advise you to add a layer of acidified compost, then add liquid seaweed with iron.

St Augustine grass yellow after fertilizing?

Did your St.Augustine lawn turn yellow after you fed it recently? This is a sign of overfertilization. Too much fertilizer causes harm too.

Excess nitrogen salts in the fertilizer burn the grass blades. This is called leaf scorch. The grass yellows at the bottom and turns brown at the top.

This happens only with quick-release fertilizers. That’s why it’s better to use slow-release fertilizers like Milorganite.

To fix:

  • If you’ve noticed scorch early, you can fix it easily. Water the lawn thoroughly. Watering the affected areas washes away excess salts present in the soil.
  • Rake and Till the affected area.
  • Resod your lawn if a large part of the lawn is affected.

Best fertilizer for yellow St Augustine grass

Scotts Turf Builder is a good fertilizer for yellowing St.Augustine grass. Add some chelated iron or Iron Sulfate if the lawn lacks iron.

Pennington UltraGreen Lawn Fertilizer and Milorganite 0636 Nitrogen Fertilizers work best to give a boost to your St.Augustine lawn.

Don’t add too much fertilizer as it can lead to scorching of the grass blades.

How to fix dead spots in St Augustine grass

Patches of dead grass surrounded by yellowing grass are a sign of Chinch bug infestation. Chinch bugs are a common pest of St.Augustine grass.

What causes Chinch Bugs?

If there’s a layer of thatch in your lawn, the lawn is more susceptible to a Chinch bug infestation. Thatch is just dead organic material.

Use a turf aerator to punch holes into the lawn and increase air movement in the lawn. This helps prevent a Chinch bug infestation.

There is a cultivar of St.Augustine grass that is resistant to Chinch bug infestation called ‘Captiva’. This cultivar is hardy in US Zones 8b-11.

Does Triazicide kill Chinch Bugs?

Spot spraying the affected areas with Triazicide would work effectively. Inspect the affected area every 3-5 days to make sure the treatment is working.

How to fix yellow St Augustine grass?

Follow the below instructions to fix your yellowing St.Augustine grass.

  • Check for any Chinch bug infection in St Augustine grass. Spray Triazicide if you notice any infection.
  • Did the St.Augustine grass turn yellow after you fertilized it recently? This is a sign of overfertilization. You can fix such a grass lawn by watering it down.
  • A fungal infection is characterized by yellow circles on grass blades. Such diseases are usually seen only in a part of the lawn. Such fungi cause root rot. You can fix such lawns by applying Myclobutanil and Azoxystrobin.
  • St. Augustine grass turns yellow in spring because the rains leech out the Nitrogen from the soil.
  • If the above issues aren’t the reason, check for iron content in the soil. If it’s low, apply Iron Sulfate to the lawn.