When To Fertilize St Augustine Grass

Knowing when to fertilize St Augustine grass is the single most important factor for achieving a thick, green, and healthy lawn. This guide will walk you through the optimal timing for healthy growth, ensuring your lawn gets the nutrients it needs exactly when it needs them.

St. Augustine is a warm-season grass that thrives in heat. Its feeding schedule is different from cool-season grasses. Getting the timing right prevents problems like disease, weed invasion, and unnecessary stress on your turf.

Your fertilization schedule is built around the grass’s natural growth cycle. The goal is to feed it during its active growing season and let it rest when it slows down.

The Best Times of Year to Apply Fertilizer

The core feeding window for St. Augustine is late spring through early fall. Here is a simple seasonal breakdown:

Late Spring (After Green-Up): Apply your first fertilizer only after the lawn has fully woken up from dormancy and is consistently green. This is usually when soil temperatures stay above 65°F. This feeding kickstarts strong growth.
Summer: Provide 1-2 more applications during the peak growing months. Space them about 6-8 weeks apart. Consistent summer feeding supports the grass as it handles heat and foot traffic.
Early Fall (6 Weeks Before First Frost): Your final application should be a fall fertilizer. It helps the grass store energy for winter and promotes better color in the spring. Never fertilize too late in fall, as it can promote tender new growth that will be damaged by frost.
Winter: Do not fertilize. The grass is dormant or growing very slowly and cannot use the nutrients.

How to Know Your Lawn is Ready for Spring Feeding

Don’t go by the calendar date alone. Your lawn will tell you when it’s ready. Watch for these two signs:

Consistent green color across about 90% of the lawn, not just a few early blades.
When you’ve had to mow it at least twice. This confirms active growth has truly begun.

Applying fertilizer too early, while the grass is still mostly dormant, feeds weeds instead of your lawn. It’s a common mistake that sets you back for the whole season.

Choosing the Right Fertilizer for St. Augustine

Not all lawn fertilizers are created equal. Using the wrong type can harm your St. Augustine.

Nitrogen (N): This is the key nutrient for green, leafy growth. Look for a balanced fertilizer where nitrogen is the first number in the N-P-K ratio (like 15-0-15 or 16-4-8).
Slow-Release vs. Quick-Release: For most homeowners, a fertilizer with at least 50% slow-release nitrogen is ideal. It feeds the grass gradually over 6-8 weeks, reducing the risk of burning the lawn and providing more even growth. Quick-release formulas can cause a rapid flush of growth that is more suseptible to disease.
Weed & Feed Products: Use these with extreme caution. Only apply a weed and feed if you have a documented weed problem that matches the herbicide in the product. Applying it preventatively can stress your St. Augustine unnecessarily.

A Note on Iron for Greener Color

Sometimes your lawn needs iron more than nitrogen. If your grass looks yellow but is growing steadily, an application of iron sulfate or a liquid iron supplement can deepen the green color without causing a growth spurt. This is especially useful in the summer when you want color without excess growth.

Step-by-Step Fertilizer Application

Doing it correctly ensures the fertilizer benefits the grass and doesn’t wash away or cause damage.

Mow: Mow your lawn 1-2 days before you plan to fertilize. Bag the clippings if they are long.
Check the Weather: Apply fertilizer when no heavy rain is forecast for at least 24 hours. A light shower after application is actually beneficial. Avoid applying during drought conditions unless you can water it in.
Calibrate Your Spreader: This is the most skipped step! Set your broadcast or drop spreader to the rate listed on the fertilizer bag. Doing a test run on your driveway helps you see the spread pattern and adjust the setting.
Apply Evenly: Walk at a steady pace, slightly overlapping your wheel tracks to avoid missed strips. Uneven application leads to striping—dark green and light green lines across your lawn.
Water It In: Thoroughly water the lawn after application. This washes the fertilizer granules off the grass blades and down to the soil where the roots can access it. Use about 1/4 to 1/2 inch of water.

Critical Mistakes to Avoid

Even with good timing, these errors can ruin your efforts.

Overfertilizing: More is not better. It leads to thatch buildup, excessive growth (meaning more mowing), and increased vulnerability to brown patch and gray leaf spot diseases. It also pollutes local waterways.
Fertilizing a Stressed Lawn: Never fertilize a lawn that is under drought stress, diseased, or covered with insects. Address those problems first, then feed the grass once it has begun to recover.
Ignoring Soil Health: Fertilizer adds nutrients, but it doesn’t fix poor soil. Every 2-3 years, consider a soil test. It will tell you exactly what your soil lacks and its pH level. St. Augustine prefers a slightly acidic pH of 6.0 to 6.5.

Adjusting for Your Specific Climate

While the general schedule is a great starting point, you may need to make small adjustments.

Florida & Deep South: Your growing season is long. You may need 3-4 applications, starting in early March and ending in late September. Be extra vigilant about summer disease pressure if you over-fertilize.
Texas & Transition Zones: Your schedule may be more compressed. Start in late April or May and finish by mid-September. Watch for early frosts in northern parts of the state.
Coastal Areas: Salt spray and sandy soil are factors. You may need slightly more frequent applications with micronutrients, as sandy soils leach nutrients quickly. Always follow soil test recommendations.

FAQ: Your Fertilization Questions Answered

Can I fertilize St. Augustine in the fall?
Yes, but timing is critical. Apply a fall/winterizer fertilizer (higher in potassium) about 6 weeks before your average first frost date. This strengthens roots for winter but won’t push top growth.

What is the best fertilizer schedule for St. Augustine?
A typical schedule is: 1) After spring green-up, 2) Early summer, 3) Late summer, and 4) Early fall. That makes four total applications for many regions.

How often should you fertilize St. Augustine grass?
During its active growth period, every 6-8 weeks is standard. The exact number of applications per year depends on your climate and the product’s release formula.

Is it too late to fertilize in October?
In most areas, yes, it is too late. Fertilizing this late can stimulate new growth that will be killed by frost, weakening the entire lawn. The exception is very southern zones where frost isn’t a concern.

Should you water St. Augustine after fertilizing?
Absolutely. Watering immediately after application moves the nutrients into the soil and prevents the granules from burning the grass blades.

By following this timing guide, you give your St. Augustine lawn the foundation it needs. Consistent, proper feeding leads to a dense turf that naturally crowds out weeds and resists pests. Remember, a healthy lawn starts with what you put into it, and more importantly, when you put it down. Paying attention to your grass’s cues and the local climate will always yield the best results for your yard.