What Causes St. Augustine Grass To Turn Yellow?

Yellow grass can be frustrating! It isn’t easy to diagnose and can be equally challenging to treat. If you are dealing with yellow St. Augustine grass, keep reading to learn more.

About St. Augustine grass

St. Augustine grass is a heat and humidity tolerant grass that can be found in many lawns in Florida and the other Gulf states. The blue green grass blades are coarse. This hardy grass variety does not need a lot of water and is salt tolerant, making it the ideal grass for lawns near the coast.

Why does St. Augustine grass turn yellow?

Iron deficiency

What is iron chlorosis? Low iron levels in the grass cause iron chlorosis. A soil pH level that is too high makes it difficult for the grass to absorb the iron in the soil.

Grass needs iron for chlorophyll development. Chlorophyll is what gives grass its nice, green color. Iron chlorosis is usually seen in St. Augustine grass in the early spring. You can tell if your grass has iron chlorosis because the grass blades will have stripes of yellow and green on the grass leaf.

Nitrogen deficiency

St. Augustine grass that is deficient in nitrogen will have solid yellow blades of grass that are turning lime green. Often, grass will become nitrogen deficient after a lot of rain or overwatering during the summer months. The excess moisture leeches the nitrogen out of the soil.

Take-All Root Rot (TARR)

Take-All Root Rot (TARR) usually shows up in the spring if soils are too alkaline. There will be yellow patches with green and yellow grass blades. If you suspect TARR, pull out a clump of grass. If it is TARR, the grass will come up easily, and the roots will be short and dark.

How do I fix yellow St. Augustine grass?

How Do I Fix Yellow St. Augustine Grass

What can I do? There is a solution to each of these problems to reverse yellowing St. Augustine grass!


Soil compaction can make it difficult for grass to absorb all the water and nutrients it needs. Aeration punches holes into the turf, allowing air and water to reach the plants’ roots. The best time to aerate is in the spring.

Iron application

If the issue is a lack of iron or iron chlorosis, the solution is as simple as an iron application. Spray a chelated iron solution onto the grass. Avoid watering until at least 24 hours after application.

Nitrogen fertilizer

Give your lawn a boost of nitrogen with a nitrogen-rich fertilizer. I recommend a nitrogen application in early summer, another one in the middle of the summer, and finish off the growing season with a final application of nitrogen. St. Augustine grass usually does best with a half-pound to a full pound of nitrogen per 1,000 square feet per application.

Peat moss

A healthy dose of sphagnum peat moss is the perfect solution to TARR. The peat moss will encourage the growth of beneficial microbes and lower the pH of the soil. Apply one to two bales of peat moss per 1,000 square feet of lawn. After application, thoroughly soak the peat moss with water.


If you cannot beat TARR with a peat moss application, try a fungicide spray. Apply it to the affected areas. Most fungicides are effective for about one month.

Final thoughts

Don’t let yellow St. Augustine grass spoil your lawn! Diagnose and treat your problem. Enjoy your green grass once again!