When Do You Fertilize St Augustine Grass

Knowing when do you fertilize St Augustine grass is the first step to a thick, green, and healthy lawn. This warm-season favorite thrives with a well-timed feeding schedule, and getting the timing right makes all the difference.

Fertilizing at the wrong time can lead to weak growth, disease problems, and wasted effort. Let’s break down the optimal calendar for your St. Augustine so you can give it exactly what it needs, exactly when it needs it.

The core schedule for fertilizing St. Augustine grass is based on soil temperature, not just the date on the calendar. The grass starts growing actively when soil temperatures consistently reach 65°F. This is your signal to begin.

In most regions where St. Augustine thrives, this means a feeding schedule from late spring through early fall. A good rule of thumb is to fertilize 2-4 times during the growing season.

The Ideal Fertilizing Calendar

Here’s a seasonal breakdown to follow:

Late Spring (First Application): Apply your first fertilizer once the grass is fully green and has been mowed at least twice. This is usually around April or May. This feeding fuels the initial surge of growth.
Early Summer (Second Application): Follow up 6-8 weeks later, around June or early July. This supports the grass through its peak growing period.
Late Summer (Optional Third Application): If your lawn needs a boost, a third light application can be done in early August. Avoid fertilizing too late in summer in hot, humid areas to reduce disease risk.
Early Fall (Final Application): The last feeding should be done about 6-8 weeks before your area’s first expected frost. This helps the grass store nutrients for winter dormancy and promotes a quicker green-up next spring. Never fertilize in winter.

Why Timing is So Critical

Getting the timing wrong can cause more harm than good. Fertilizing too early or too late stresses the grass.

Too Early (Early Spring): If you fertilize before the grass has fully exited dormancy, you feed weeds instead and can promote tender growth that is suceptible to a late frost.
Too Late (Fall/Winter): Fertilizing as the grass is slowing down forces new, soft growth that is easily damaged by cold. This weakens the plant and can lead to winter kill.

The Role of a Soil Test

Before you even buy fertilizer, a soil test is your best investment. It tells you exactly what nutrients your soil lacks. You might not need a high-nitrogen blend if your phosphorus or potassium is low. Contact your local county extension office for a cheap and reliable test kit.

Choosing the Right Fertilizer

Not all lawn fertilizers are created equal. For St. Augustine, look for a product with the right N-P-K ratio.

Nitrogen (N): This is key for green, leafy growth. St. Augustine needs a steady supply.
Phosphorus (P): Supports root development. Your soil test will indicate if you need it.
Potassium (K): Promotes overall plant health, drought tolerance, and disease resistance.

A common and safe ratio for St. Augustine is 3-1-2 or 4-1-2 (like 15-5-10 or 16-4-8). Also, consider using a slow-release or controlled-release nitrogen fertilizer. It feeds the grass gradually over time, preventing a rapid flush of growth that attracts pests and reduces the risk of nutrient burn.

How to Apply Fertilizer Correctly

Proper application ensures the grass gets the food without any damage. Follow these steps:

Mow: Cut your lawn a day or two before you plan to fertilize. Bag the clippings if they are long.
Check the Spreader: Ensure your broadcast or drop spreader is clean and calibrated. The fertilizer bag will have settings instructions.
Apply Evenly: Overlap your passes slightly to avoid missed strips or doubled-up lines, which can cause striping or burning.
Water In: Lightly water the lawn after application. This helps move the fertilizer granules off the grass blades and into the soil. You don’t need to soak it, just a good quarter-inch of irrigation.

Special Considerations for Different Regions

Your local climate slightly adjusts the calendar.

Florida & Deep South: You may start a bit earlier (March-April) and can often fertilize up to 5 times, but always follow local ordinances which may restrict summer nitrogen use to protect waterways.
Texas & Transition Zones: Stick closely to the late spring to early fall window. Watch for early frosts in the fall.
Coastal Areas: Be mindful of salt spray. Using a fertilizer containing potassium can help improve salt tolerance.

What to Avoid: Common Fertilizing Mistakes

Even with good timing, errors in practice can hurt your lawn.

Over-fertilizing: More is not better. It leads to excessive thatch, fungal diseases like brown patch, and pollution from runoff.
Fertilizing During Drought: If your lawn is stressed and brown from lack of water, do not fertilize. Water it deeply first and wait for it to recover.
Ignoring Weed & Feed Products: Be cautious with combination products. Apply them only if you actually have the weed problem they treat, and never during lawn stress periods.
Forgetting to Water In: Leaving granules on blades can cause sun magnification burns, leaving ugly yellow spots on your lawn.

Signs Your Fertilizer Schedule is Working

When you get the timing right, your lawn will show it.

Consistent, steady green color throughout the growing season.
Thick turf that crowds out weeds naturally.
Good recovery from foot traffic or minor damage.
Reduced incidence of disease and pest issues due to overall plant health.

FAQ: Your Fertilizer Questions Answered

What is the best month to fertilize St. Augustine?

The best starting month is usually late April or May, once the soil is warm. The most important month for the final feeding is September, about 6 weeks before frost.

Can I fertilize St. Augustine in the summer?

Yes, but with caution. An early summer feeding (June) is standard. A late summer (August) feeding should be light, and avoided in very humid regions to prevent disease.

Should you fertilize St. Augustine in the fall?

Yes! An early fall application is crucial for root development and winter storage. This is often considered the second most important feeding after the spring starter.

Is it too late to fertilize in October?

In most regions, yes, it is too late. Fertilizing this late risks winter injury. The exception would be very southern areas where the grass remains active.

How often should I fertilize my St Augustine lawn?

Plan for 3-4 feedings per year: late spring, early summer, possibly late summer, and early fall. Your soil test and lawn appearance are the best guides for frequency.

By following this simple calender and paying attention to your lawns specific needs, you’ll provide the nutrients for a resilient and beautiful St. Augustine lawn. Remember, consistency with timing and proper application technique are just as important as the fertilizer you choose. Your grass will thank you with lush, green growth all season long.