The tropical St. Augustine grass is a warm-season grass for lawns and yards in Zones 7 to 12.
It doesn’t require a lot of maintenance but pays back for your care with a lush green lawn that makes you the envy of the neighborhood.
When the grass starts to turn yellow, you need to check for the causes and remedy them.
What causes St. Augustine grass to turn yellow? St. Augustine grass will turn yellow if it’s not getting enough water or receives too much water in a short time period. Soil poor in nitrogen or iron can also cause the grass to turn yellow. Pests, diseases, over-fertilization, short mowing, and extreme temperatures are possible causes too.
More often than not, more than one of these causes combine together to give St. Augustine grass that sickly and pale look.
Continue reading to find out what causes the grass to turn yellow and how to revive it.
Yellow St. Augustine Grass – 11 Reasons + Solutions
The highly ornamental St. Augustine grass is a member of the Poaceae family. That makes it a true grass. The healthy leaves are bluish-green and create a dense mat, making it ideal for lawns.
Since it can tolerate salty environments, it does well on lawns along the coastal areas, but when the growing conditions are less than ideal, those leaves will lose their colors and turn yellow.
Here are the top 11 causes of that problem.
1. Lack of Water
St. Augustine grass prefers the soil to be steadily moist throughout the growing season in the spring and summer. Drought causes the grass to wilt and turn yellow rather quickly, especially in the first year.
Once it establishes, you can allow the top one inch of the soil to dry out between irrigations. Give the grass 1 inch of water a week, and factor in the rainfall.
2. Too Much Water
Overwatering is a problem for St. Augustine grass, and it leads to root rot. This damage to the roots causes the leaves to lose their bluish-green color.
Make sure the soil drains well, and allow it to dry between irrigations. Check the top of the soil with your finger. If it’s dry, water the grass. Otherwise, wait until it dries.
3. Lack of Nitrogen
St. Augustine grass needs lots of nitrogen in the soil. Poor soil that lacks nitrogen will stunt the growth of the grass.
Apply a quality lawn fertilizer with high nitrogen content (this one is ideal) to fix this problem. You might need a few applications before the grass revives and regains its natural colors.
4. Iron Deficiency
Iron deficiency causes yellow streaks and spots to appear on the blades of St. Augustine grass.
This condition is called iron chlorosis, and it leaves the lawn looking like a patchwork of different shades of yellow.
Use foliar-applied liquid iron to fix this problem. Another option is to use chelated iron supplements. However, these supplements are quite expensive.
5. Too Much Fertilizer
As a heavy feeder, St. Augustine grass needs regular fertilizer once every 6 to 8 weeks during the spring and summer.
However, if you give the grass too much fertilizer, this will cause root burn and damage the structure of the grass.
Avoid fertilizing the grass in the fall and winter, and limit the spring and summer applications to once every 2 months until it recovers.
6. Fungal Infection or Disease
St. Augustine grass is prone to all kinds of fungal infections from root rot and gray leaf spot disease to downy mildew.
The infections spread during warm and wet conditions, especially after rainfall. You’ll find patches of yellow on the lawn and in severe cases, large areas will die.
Dig out the infected areas, and expose the soil to the sun before reseeding the area.
Of all the pests that attack St. Augustine grass, chinch bugs are by far the most destructive.
These pests are not content to just eat the leaves and stems of the grass. They also inject it with toxins that cause the leaves to lose their color and wilt.
Prevent chinch infestations by keeping the grass watered and dethatching it regularly.
8. High Temperatures
St. Augustine grass is a warm-season grass that can handle temperatures between 80 to 100 degrees Fahrenheit.
However, if the temperature exceeds the high end of that range, the grass will wither as it loses moisture faster than the roots can replenish it.
Shrubs and leafy trees can cut the heat and help keep the grass cool in the summer.
9. Poor Soil Quality or Compaction
Loamy soil is ideal for St. Augustine grass. It drains quickly and doesn’t retain the water more than the roots of the grass need it.
If the soil is clay or of poor quality, the roots of the grass will have trouble developing.
Amend the soil with perlite to improve its texture. Hold a fistful of the soil, and clamp it in your hand. If the soil becomes compact, add more perlite.
10. Pet Urine
Pets have no problem relieving themselves on the grass. Pet urine contains ammonia and chemicals that practically kills the grass.
Dig up the yellow patches, and reseed with St. Augustine seeds. Fertilizer and water regularly until the seeds germinate. Alternatively, use sod to fill empty patches.
Meanwhile, keep the pets off the lawn or train them to relieve themselves away from the grass.
11. Lawn Mowed Too Short
When you mow your St. Augustine grass, you should keep it between 2 to 3 inches tall.
If you cut it lower than 2 inches, there’s a chance you’ll expose the turf to the harsh light and cut the nutrition supply to the leaves. This causes them to lose their lush bluish-green color.
Fertilize the lawn, and allow it to grow back. The leaves will regain their color in a week or two.
St. Augustine Grass Fertilization
As much as St. Augustine grass needs nutrients, especially nitrogen and iron, overfertilization can backfire and cause root burn.
On average, you should feed the grass from the early spring until late summer. Apply an all-purpose lawn fertilizer once every 6 to 8 weeks.
At the end of the summer, hold off fertilization until the next spring.
Spread the fertilizer granules by hand evenly going in one direction from north to south. Then repeat going from east to west.
Walk in straight lines to avoid overfertilizing some spots. Water after every application to prevent root burn.
How Fast Does St. Augustine Grass Grow?
St. Augustine grass takes between one and two weeks to develop a dense mat of healthy leaves. This is good news if you need to fill in some bare spots on the lawn.
Within a couple of weeks, the lawn will look even and uniform.
How To Make St. Augustine Grass Thicker?
Soil pH levels are the key factors in making St. Augustine grass thicker. Maintain slightly acidic soil with levels between 6.0 and 6.5. Amend the soil with sulfur to maintain these levels.
St. Augustine grass is a warm-season grass ideal for lawns in Zones 7 to 11.
If the bluish-green leaves turn yellow, check that the grass is getting adequate amounts of water, the soil is loamy and has enough nitrogen and iron in it, and that the grass is not infected with fungal diseases.