St Augustine Grass Turning Yellow? 10 Reasons + Fixes

St Augustine grass makes up a beautiful lawn due to its dark green coloration and broad leaves. One of the common St Augustine lawn problems is the grass turning yellow. 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 grass yellowing as a result of pests attack, diseases, extreme temperatures and fertilizer burns.

Why is My St Augustine Grass Turning Yellow?

The following are the main reasons why St Augustine grass may turn yellow and what to do.

1. Nitrogen Deficiency

A low level of nitrogen in the soil is can cause yellow leaves in the grass. Nitrogen form the main component of chlorophyll which give plants a green color. Its deficiency may result from poor soil or heavy rainfall which may leach the nutrients deep into the soil beyond grass roots’ reach.

How to Fix

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 the lawn after fertilizing.

2. Iron Deficiency

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

A 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.

How to Fix

If the issue is arising from iron deficiency, apply a chelated iron solution on the grass. Lower the soil pH to allow the 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. Over-fertilization

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

How to Fix

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

Fixing lawn fertilizer burn is not instant. You can start by watering thoroughly the affected area. This will help in diluting the fertilizer and reduce its burning effect. If watering won’t revive the grass, then you have to remove the dead grass and reseed your lawn.

4. Excess Water

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

Fungi also thrive in warm and damp places. Waterlogged spots in your lawn will create a suitable breeding ground for fungal infections.

How to Fix

Drive away any standing water in the yard. Find the cause of this problem and provide a solution. Fix any faulty drainage or plumbing issues, and level your lawn to remove any low areas where water can stand.

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 feels dry.

5. Extreme Temperatures

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

How to Fix

Watering your lawn is enough to keep the grass cool in the extreme heat of summer. On average, St. Augustine grass requires about ¾ inch of water twice per week. The grass may need even more water during a dry summer season.

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 becomes unable to absorb water, oxygen and nutrients from the soil. The uncontrolled fungal infection will cause thinning and eventually death of grass.

How to Fix

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.

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.

How to Fix

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

Severe infestation can be managed through the application of insecticides. Be sure to read and follow the manufacturer’s instructions on the product label.

8. Dog Urine Spots

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

How to Fix

To treat dog urine spots on the lawn, simply water the affected area thoroughly. This will help in diluting and spreading the excess nitrogen to levels that can be handled by the grass. Further fence or use motion-activated deterrents to keep away dogs and cats.

9. Soil Compaction

Heavy traffic and the presence of clay soil can result in compacted lawn soil. The hardened soil makes it difficult for water, air and nutrients to penetrate and reach the grassroots. As a result, your lawn grass will become unhealthy despite watering or fertilizing.

How to Fix

If you suspect soil compaction, then aerate the soil by creating punch holes in the turf. It allows free air and water movement into the soil to reach the roots.

10. Thatch Buildup

Thatch is a collection of dead grass and other debris on the base of the grass. A low amount of thatch can be helpful to grass; it is a source of organic nutrients to the soil and also a cover against moisture loss or heat penetration to the plant roots.

Excess buildup of thatch on the other hand is a threat to your lawn grass. It may harbour insects and other pests or prevent sunlight, water and nutrients from reaching the grassroots. As a result, your grass will start turning yellow as of the distress of starvation.

How to Fix

The solution to this problem is straightforward. Simply check if thatch is over ½ inch thick and dethatch your lawn. If this was the problem affecting your grass, it will only take a few weeks to notice a change in color.

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. A 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 the 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 lower the soil pH to the 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 the grass to turn green. Taking too long to determine the issue will continue to subject the grass to yellowing.

Final Thoughts

When having St Augustine lawn grass, it’s common to experience various challenges. At some point, you will notice the yellowing of leaves. This problem usually results 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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