Why Is My St. Augustine Grass Turning Yellow? Here’s How to Diagnose and Treat It

A lush green lawn is the pride and joy of many homeowners. But when those emerald blades start turning yellow, it can be incredibly frustrating. As a landscaper with over a decade of experience, I’ve seen my share of yellowing St. Augustine lawns. And believe me, it’s a common issue that can have many different causes.

The truth is, yellow grass is usually a sign that something is wrong. Whether it’s disease, improper care, or environmental stressors, yellowing indicates your lawn needs a little TLC. The good news is, with the right diagnosis and treatment, you can get your St. Augustine back to its former green glory.

In this article, I’ll draw from my years of hands-on experience to explore the top reasons you may see yellowing in your St. Augustine lawn. I’ll also provide helpful tips to cure and prevent yellowing, so you can have the lush, envy-of-the-neighborhood lawn you desire.

From overwatering issues to nitrogen deficiency and disease, we’ll cover all the common culprits. I’ll also discuss how weather, lawn care mistakes, and other factors can contribute to your grass turning yellow. Consider this your master guide to diagnosing and treating yellowing in St. Augustine grass.

Let’s get growing! In the following sections, I’ll dig into the details on each potential cause of yellowing and how to fix it.

Overwatering Can Cause Yellowing in St. Augustine Grass

As a landscaper, I can’t stress enough how important proper watering is for a healthy lawn. Overwatering is one of the most common reasons St. Augustine grass turns yellow. Too much moisture prevents the roots from getting oxygen, causing damage that shows up as yellow, thin turf.

It’s easy to overdo it with the sprinklers, especially in the summer. St. Augustine thrives in heat and humidity, so it needs less watering than cool-season grasses. The key is to water deeply but infrequently, saturating the soil to a depth of 4-6 inches. Shallow sprinkling every day trains the roots to stay near the surface, making them vulnerable.

Signs of Overwatered Grass

How do you know if you’re overwatering your lawn? Here are some telltale clues:

  • Mushy, squishy soil – If you step on the lawn and water oozes up, it’s way too wet. Healthy soil should be moist but firm.
  • Visible puddling – Low spots that stay soggy hours after irrigation indicate poor drainage.
  • Footprints linger – Grass blades slowly bounce back after being stepped on when overwatered.
  • Yellow patches – Excess moisture damages roots and deprives grass of nutrients.
  • Thin, weak turf – Overly saturated soil suffocates roots, preventing nutrient uptake.
  • Excessive growth – Too much water generates succulent, tender blades prone to disease.

Adjust Your Watering Schedule

If you suspect overwatering, cut back on irrigation time and frequency. Here are some tips:

  • Water early morning before heat builds. Avoid evening watering which increases fungus risk.
  • Check soil moisture before watering. Probe with a screwdriver to test depth. No need to add water if top 4 inches are damp.
  • Make sure sprinklers fully cover area without overlap. Adjust as needed.
  • Install a smart controller to automatically adjust for weather conditions.
  • Switch sprinkler nozzles to more efficient models. New rotor and spray head designs conserve water.
  • Set cans in sprinkler zones to measure output. Adjust run times so each zone applies 3/4 to 1 inch per session.
  • Let grass grow taller – longer roots access moisture deeper in soil. Raise mower height to 3-4 inches.

With some adjustment, you can maintain moisture levels that keep your St. Augustine lush without overdoing it. The key is paying close attention and making tweaks over time. A perfectly dialed-in watering schedule takes patience, but it’s worth it for a flawless green lawn.

Nitrogen Deficiency Turns St. Augustine Grass Yellow

As a master gardener, I always say healthy grass starts from the roots up. And when it comes to root health and vigorous growth, nitrogen is job one. This key nutrient promotes deep roots, green color, and thick turf. When nitrogen is deficient, St. Augustine blades turn pale yellow.

Nitrogen fuels the production of chlorophyll, the green pigment in plants. Without adequate nitrogen, grass struggles to manufacture enough chlorophyll to maintain rich color. Deficiency also stunts root development, reducing the plant’s ability to take up water and nutrients from the soil. Weakened roots lead to thinning and yellowing of the turf.

Generally, St. Augustine needs about 4-6 pounds of nitrogen per thousand square feet annually. Hot, humid climates and sandy soils call for the higher end of the range. Heavy clay soils that don’t leach nutrients may need less.

Testing is the best way to pinpoint any shortfall. A complete soil test through your local extension service or private lab will measure nitrogen and other nutrients. Home test kits are also available for quick nitrogen readings. Based on results, you can determine precisely how much to add.

Applying a high-quality nitrogen fertilizer provides an immediate remedy. Slow-release products are ideal for steady uptake over 6-8 weeks. I’m partial to methylene urea fertilizers which break down gradually with irrigation and rain. For quicker green-up, soluble nitrogen sources like ammonium sulfate can supplement slow-release fertilizers. Just be careful not to overdo it, as excessive nitrogen invites disease and weak growth.

When it comes to fertilizing St. Augustine, a little goes a long way. Follow product labels and test results for optimal nitrogen rates. With the right balance, you’ll maintain healthy roots, vigorous growth and rich emerald color all season long.

Diseases Like Brown Patch Cause Yellowing to St. Augustine Grass

As a horticulturist, I’ve seen my share of tricky turf diseases. And when it comes to St. Augustine grass, brown patch is public enemy number one. This fungal infection can spread quickly under the right conditions, causing yellowing and dieback.

Brown patch thrives during periods of warm, wet weather. It’s most active at night, attacking the grass blades and crowns. The disease starts out as dark, water-soaked spots that expand rapidly under fertile conditions. As the fungus chokes off water and nutrients, the grass weakens and yellows.

On close inspection, the margins of brown patch areas have a smoke ring-like pattern. The fungus produces this effect as it moves outward. Severely damaged patches turn brown and straw-like as the grass dies.

To treat active brown patch, fungicides containing myclobutanil, propiconazole or azoxystrobin work well. Apply at the first sign of disease and repeat every 7-14 days as needed. Improve drainage in low spots and irrigate early in the day to reduce the amount of time blades stay wet.

Prevention is key to avoid major flare-ups. Maintain proper fertilization, mowing and irrigation to encourage vigorous grass. Avoid excess nitrogen which produces succulent growth vulnerable to infection. Thatch buildup also increases brown patch risk, so dethatch in spring or fall.

While brown patch poses the biggest disease threat, other fungal issues can also cause yellowing. Gray leaf spot shows up as lesions on blades, while take-all patch creates thinning patches. Dollar spot produces small sunken spots outlined in white fungal growth. Regular disease prevention practices keep all these problems in check.

Caught early, brown patch and other diseases are manageable. But at the first sign of infection, prompt treatment combined with cultural practices enhances control and minimizes yellowing damage. Maintaining optimal turf health and vigour is the best long-term disease prevention strategy.

Extreme Weather and Improper Care

In my many years as a lawn pro, I’ve seen all kinds of stresses turn St. Augustine grass yellow. From scorching heat waves to frigid cold snaps, extreme weather can take a toll. Simple lawn care mistakes like overmowing or poor drainage only make matters worse. Managing environmental factors along with proper turf care practices prevents yellowing issues.

Hot, dry weather puts significant pressure on St. Augustine. Prolonged drought causes drought stress, where grass struggles to extract moisture from parched soil. As plants dehydrate, photosynthesis shuts down and blades turn yellow. Providing supplemental irrigation prevents drought stress damage. When temperatures exceed 90°F, leaf tissue scorches and browns in a condition called heat stress. Allowing grass to grow taller creates a shading effect that protects from heat damage.

While St. Augustine thrives in southern climates, cold snaps can still cause yellowing. Prolonged exposure to freezing temperatures damages cell structures. This leads to yellow, slowed growth in spring. Gradually bringing lawns out of winter dormancy minimizes cold shock. Rake out matted layers to speed spring green-up.

Mowing too short is another common culprit for yellowing. St. Augustine should be cut to 3-4 inches tall. Scalping causes weakened, stressed plants. Adjust mower height up and never remove more than 1/3 of blade length when cutting. Proper mowing technique produces deeper roots and denser turf.

Finally, poor drainage triggers yellowing and thin spots. St. Augustine needs well-draining soil to thrive. Improve drainage by aerating compacted areas and topdressing with compost. Ensure sprinklers deliver even coverage to avoid puddles. Installing French drains alleviates standing water.

No grass is immune to environmental stresses and lawn care mistakes. But by managing weather disruptions and following proper care practices, you can keep your St. Augustine greener and healthier all year round. Vigilant maintenance combats whatever Mother Nature throws your way.

Frequently Asked Questions

In my years as a lawn care specialist, I’ve fielded plenty of common questions about restoring yellow St. Augustine grass. Here I’ll cover some of the key FAQs to address reader concerns.

How Long Does It Take for Grass to Turn Green Again After Yellowing?

This is one of the most frequent questions I get. The time it takes for your lawn to regain its green color depends on the underlying cause. For mild nutrition or watering issues, you may see improvement within 2-4 weeks. Severe disease damage can take 4-8 weeks to fully repair. Overseeded areas also require 3-5 weeks of growth before filling in.

No matter the cause, patience is crucial. Grass plants grow slowly, so recovery doesn’t happen overnight. With proper care, you should see gradual green return in affected areas. Spot treat yellow sections as needed while waiting for turf to rebound.

Is St. Augustine More Prone to Yellowing Than Other Grasses?

Compared to other warm season grasses, St. Augustine is moderately susceptible to discoloration issues. Bermuda grass is less prone to yellowing, while centipede grass is more sensitive. Proper cultural practices tailored to St. Augustine’s needs minimize yellowing.

Its sensitivity to overwatering and disease makes St. Augustine more likely to yellow than bermuda. But it holds up better than centipede, which thins out when stressed. Following best care guidelines keeps St. Augustine greener than other grasses.

Should I Overseed My Lawn to Prevent Yellowing?

Overseeding with ryegrass helps St. Augustine lawns stay green in winter when cool-season rye thrives. But for preventing summer yellowing, overseeding isn’t necessary. Proper mowing, fertilizing, watering and disease prevention maintains healthy color in warm months.

Ryegrass needs reseeding annually since it dies in summer. This extra cost and labor isn’t required simply to curb yellowing. For non-dormant St. Augustine, concentrate on improving care practices rather than overseeding.

Conclusion and Final Tips

After covering all the potential causes and fixes for yellowing St. Augustine grass, hopefully you now feel equipped to get your lawn back to its former emerald glory. As we’ve discussed, yellowing is usually an indication that something in the lawn environment needs adjustment. Stay vigilant for early signs of problems and be prepared to take prompt corrective action.

When you notice yellowing, walk the lawn and examine blades and soil to diagnose potential causes. Check for signs of overwatering, diseases, drought stress, mowing issues, etc. Use the solutions outlined in this article to treat the specific problem. With the right intervention, your grass should green back up in a few weeks.

Prevention is ideal to avoid yellowing in the first place. Maintain optimal care practices like proper mowing, fertilizing, irrigation and disease control. Do routine maintenance like aerating, dethatching and topdressing to encourage deep roots and healthy soil. Adjust care as needed based on weather fluctuations and lawn requirements.

Finally, don’t hesitate to call in a professional for help diagnosing stubborn yellowing issues. A landscape company can assess your lawn, identify underlying problems and recommend tailored solutions for restoration. With their expertise and products, your lawn can look lush again in no time.

While yellowing may seem like a catastrophe, in most cases it’s a temporary setback that can be corrected. Arm yourself with knowledge of common causes and solutions. Stay vigilant in care and act quickly when needed. With a proactive approach, you can keep your St. Augustine greener and weed-free year after year. Your lawn will once again be the envy of the neighborhood in no time.

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