St Augustine Grass Turning Yellow? Why + Fixes

St Augustine grass makes up a beautiful lawn due to its dark green coloration and broad leaves. However, you may encounter different challenges when maintaining this grass. Many gardeners have complained about their lawn grass yellowing. So, why is St Augustine grass turning yellow?

St Augustine grass can turn yellow due to nutritional deficiency or poor watering habits. Some gardeners have also reported yellowing due to pests attack, diseases, extreme temperature and fertilizer burns. Maintaining your lawn properly can help to fix this problem.

Why is my St Augustine Grass Turning Yellow?

St Augustine grass turning yellow usually result from nutritional deficiencies related to soil alkalinity, poor drainage, drought, pest, diseases and compaction of the soil. Let’s look at some of the causes:

1. Nitrogen Deficiency

Low level of nitrogen in the soil is can cause yellow leaves in grass. Nitrogen form the main component of chlorophyll which give plants a green color. Its deficiency is common during heavy rainfall season as nutrients may leach deep into the soil beyond grass roots’ reach.

2. Iron Deficiency

Iron deficiency will cause yellowing of grass. This deficiency arise from high soil alkalinity. High soil pH prevent plants from absorbing iron and other nutrients from the soil.

Low level of iron in the soil is characterized by streaks of green through a prominent yellow leaf. Severe cases are also characterized by brown margins on the yellow leaves.

3. Over-fertilization

Over-fertilizing with synthetic fertilizers can be detrimental to your grass. Nitrogen has scorching effects on grass when applied excessively. It cause yellowing of leaves from the base, browning of grass blades on the margin and slow growth rate.

Generally, it is recommended to apply one pound of nitrogen fertilizer per 1,000 square feet of lawn. If you apply above these ratio, you will end up with yellow or burnt lawn grass.

4. Excess Water

St Augustine grass thrives well in drained soil. Waterlogged areas in the lawn will cause the grass to turn yellow. Excess water can rot the roots and prevent the grass from absorbing air and nutrients. The water can also leach nutrients deep into the ground where the roots are unable to reach.

Fungi also thrives well in warm and damp places. Waterlogged spots in your lawn will create suitable breeding ground of fungal infections.

5. Extreme Temperatures

St Augustine is a warm-season grass which can tolerate temperature range of 80 to 100 degrees Fahrenheit (27 to 38 degrees Celsius). However, it has low tolerance to prolonged drought. High summer temperatures with inadequate water will cause grass to turn yellow.

6. Fungal Infections

Large yellow or brown spots in your lawn grass result from fungal infection. Rizoctonia solani is a type of fungus that causes this condition. It’s common in warm and humid weather conditions. Moist and shaded areas in the lawn are commonly affected.

Fungal infections can also cause root rot. The grass become unable to absorb water, oxygen and nutrients from the soil. Uncontrolled fungal infection will cause thinning and eventually death of grass.

7. Insect Infestation

St Augustine grass is usually affected by chinch bugs. They are common when the grass has a lot of thatch. Chinch bug infestation is characterized by circles of yellow grass leaves. When not controlled chinch bugs can cause patches of dead grass in your lawn.

8. Dog Urine Spots

Yellow patches in your lawn may also result from dog urine. High level of nitrogen in the urine can burn the grass. Stray dogs have a tendency of marking their territory by urine whenever they visit a new place. They are likely to urinate on the grass when they visit your lawn.

Will Yellow St Augustine Grass Turn Green?

It’s frustrating to see your St Augustine grass turn yellow especially if you don’t know why. However, you don’t need to worry. The grass will turn green once the underlying cause is diagnosed and fixed.

Get your lawn soil tested to determine what is ailing St Augustine grass. Soil test will help to: Know the current condition of the soil and how to improve it, avoid over-fertilization by providing the exact quantities of nutrients required by plants and determine the pH of soil.

For instance, if the soil test results show low nitrogen levels. You can use a quick-release nitrogen fertilizer to fix yellowing St Augustine grass. The grass will be able to turn green within a few weeks.

St Augustine grass thrives in slightly acidic soil. If the soil test results indicate high alkalinity, you will be required to apply sulfur to bring it within recommended range. High alkalinity can reduce the ability of plants to absorb iron and other nutrients from the soil. Amending the soil will help the grass to turn green fast.

It’s also important to inspect the plant thoroughly for symptoms of pests and diseases. Timely treatment or control of pests and diseases can help to the grass to turn green. Taking too long to determine the issue will continue to subject the grass to yellowing.

How to Fix Yellowing St Augustine Grass

Here are some of the tips on how to fix yellowing St Augustine grass:

1. Fertilize your lawn appropriately

Fertilize your lawn with a nitrogen-rich fertilizer to fix yellowing. It is recommended to fertilize in spring when the grass is vigorously growing. You can also fertilize early and mid-summer. However, be sure to water in the fertilizer.

2. Apply iron supplements

If the issue is arising from iron deficiency, apply a chelated iron solution on the grass. Lower the soil pH to allow absorption of iron and other nutrients. Apply 5 lbs. of sulfur pellets per 1,000 square feet of lawn. St Augustine grass thrives well in slightly acidic soil with a pH range of 6.0 to 6.5.

3. Water appropriately

Both inadequate and excess water can cause your lawn grass to turn yellow. It is recommended to water the grass once or twice a week. If the weather is cool and the rate of evaporation is low, stop watering and resume when the soil feel dry.

4. Mow the lawn often

Pests like chinch bugs can hide in layers of thatch in your lawn. Mow the lawn often and keep it clean to control the pests. However, be sure to use a sharp blade. Blunt mower blade can damage the grass blades and cause yellow leaves after mowing.

5. Treat fungal infections

To turn yellow grass to green fast, control infections as soon as you see the symptoms. Spray fungicides on the affected areas and improve drainage. Most fungicides are effective, you should be able to see a positive change within a month.

6. Aerate the soil

It is difficult for roots to absorb water and nutrients in a compact soil. Aerate the soil by creating punch holes in the turf. It allow free air and water movement into the soil to reach the roots.

Final Thoughts

When having St Augustine lawn grass, it’s common to experience various challenges. At some point you will notice yellowing of leaves. This problem usually result from several causes as explained above. Diagnose the situation early and come up with a solution to save the grass from yellowing.

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