Knowing when to fertilize St Augustine grass is the single most important factor for achieving a thick, green, and healthy lawn. Fertilizing St. Augustine grass is most effective when timed with its peak growth periods in late spring and early fall. Getting this timing right feeds the grass when it can use the nutrients most efficiently, leading to robust growth and better resistance to weeds, drought, and disease.
This guide will walk you through the complete seasonal schedule, explain how to choose the right fertilizer, and provide clear steps for application. You’ll learn not just the best dates, but the soil conditions and grass signals to watch for.
When To Fertilize St Augustine
The ideal fertilization schedule for St. Augustine grass follows its natural growth cycle. This warm-season grass wakes up in the spring, grows vigorously in the summer, and slows down in the fall before going dormant in winter. Your goal is to provide nutrients just before and during these active growth phases.
The Core Fertilization Schedule
For most regions where St. Augustine thrives, a balanced approach of 2 to 4 feedings per year works best. The exact number depends on your local climate and soil health.
First Application: Late Spring
Apply your first fertilizer in late spring, after the grass has fully greened up and is actively growing. This is typically when soil temperatures consistently reach 65°F (18°C) and all danger of frost has passed. For many, this aligns with late April through May.
- Why then? The grass has used its winter energy stores and is ready for a nutrient boost to support rapid leaf and runner (stolon) growth.
- Key Signal: Your lawn should have been mowed at least twice after breaking dormancy.
Second Application: Early Summer
A second feeding in early summer, around June, helps sustain growth through the heat. This is especially important if you have a single spring feeding or if your soil is sandy and leaches nutrients quickly.
Third Application: Late Summer / Early Fall
The most crucial feeding after spring is in late summer to early fall, approximately 6-8 weeks before your area’s first expected frost date. Think late August to September. This application strengthens the grass’s root system for winter survival and provides energy storage for a strong spring green-up.
- Critical Rule: Do not fertilize too late in fall. This can promote tender new growth that will be damaged by frost and weaken the entire lawn.
Optional Fourth Application
In warmer coastal or deep southern climates with longer growing seasons, a fourth, lighter application in mid-summer may be beneficial. Always base this on the grass’s appearance and a soil test.
Regional Timing Adjustments
Your local climate dictates precise timing. Here’s a general regional breakdown:
- Florida & Deep Gulf Coast: Start in March/April, with follow-ups in June, September, and sometimes November.
- Texas & Southwest: Begin in April/May, with a summer feeding in June/July and a final fall feeding in September.
- Transition Zone (e.g., Georgia, Carolinas): Start in May, with a possible June feeding and a must-do fall feeding in early September.
Your county extension service is the best resource for localized dates.
Signs Your Lawn Needs Fertilizer
Beyond the calendar, your lawn will show visual cues that it needs nutrients.
- Pale Green or Yellow Color: A general lightening of color often indicates nitrogen deficiency.
- Slow Growth: If growth seems stunted despite adequate water and warmth.
- Thinning Turf: Bare patches or a failure to thicken up can signal a lack of nutrients to support runner growth.
Remember, these symptoms can also indicate other problems like pest or disease, so consider all factors.
Choosing The Right Fertilizer For St. Augustine
Selecting the correct product is as important as timing. Using the wrong type or ratio can harm your lawn.
Understanding NPK Ratios
The three numbers on a fertilizer bag represent the percentage of Nitrogen (N), Phosphorus (P), and Potassium (K). For St. Augustine grass, look for a ratio where the first number (Nitrogen) is the highest.
- Nitrogen (N): Promotes lush, green leaf and stem growth. St. Augustine requires a steady supply.
- Phosphorus (P): Supports strong root development and establishment. Most established lawns have sufficient phosphorus.
- Potassium (K): Enhances overall plant health, drought tolerance, and disease resistance.
A good balanced ratio for St. Augustine is something like 3-1-2 or 4-1-2. A 15-5-10 or 16-4-8 blend are common examples.
Soil Testing: The Essential First Step
Before you buy any fertilizer, conduct a soil test. This inexpensive test, available through your local extension office, tells you exactly what nutrients your soil lacks. It prevents over-application, saves money, and protects the environment.
- Collect soil samples from 4-6 random spots in your lawn.
- Mix them together in a clean bucket.
- Send the recommended amount to the testing lab.
- Follow the specific recomendations provided in the report.
Types Of Fertilizer: Quick-Release Vs. Slow-Release
This distinction is crucial for health and safety of your lawn.
Slow-Release Nitrogen
This is the preferred choice for St. Augustine. It feeds the grass gradually over 6-10 weeks, providing a steady nutrient supply without causing a rapid, excessive growth surge. It reduces the risk of fertilizer burn and leaching into waterways.
Quick-Release Nitrogen
This provides nutrients immediately, causing a fast greening effect. However, it can lead to rapid, weak growth, increased mowing, and a higher risk of burning the lawn if not applied perfectly. It’s best used by experienced lawn carers or as a starter fertilizer for new sod.
Specialty Fertilizers And Additives
You may encounter products with added iron or weed control.
- Iron Supplements: Can enhance green color without promoting excessive growth, useful for a mid-summer color boost.
- Weed-and-Feed: Combines fertilizer with herbicides. Timing is tricky, as the weed control component often needs applying when weeds are actively growing, which may not align with the best fertilizing time. Use with caution and follow label directions exactly.
How To Apply Fertilizer Correctly
Proper application technique ensures the fertilizer reaches the soil and roots safely and effectively.
Step-By-Step Application Guide
- Mow and Water: Mow your lawn a day or two before application. Water the lawn lightly the day before if the soil is very dry.
- Calibrate Your Spreader: Whether using a broadcast or drop spreader, set it to the rate specified on the fertilizer bag. This is critical for even coverage.
- Apply Around the Perimeter: Start by walking around the outer edge of your lawn with the spreader engaged.
- Fill in the Center: Walk in parallel, slightly overlapping lines to cover the entire area uniformly. Avoid overlapping to much to prevent streaks or burn lines.
- Water Thoroughly: After application, water the lawn deeply with about 1/4 to 1/2 inch of water. This washes the fertilizer granules off the grass blades and into the soil, activating the nutrients and preventing burn.
What To Avoid During Application
- Do not apply fertilizer to wet grass, as it can stick to blades and cause burning.
- Avoid applying before heavy rain, which can cause runoff and pollution.
- Never exceed the recommended application rate on the bag. More is not better.
- Keep fertilizer off driveways and sidewalks; sweep it back onto the lawn.
Seasonal Lawn Care Integration
Fertilizing doesn’t happen in isolation. It works in tandem with other seasonal tasks.
Spring Startup
In early spring, focus on preparation. Dethatch if needed, address early weeds, and apply a pre-emergent if crabgrass is a problem. Wait until the grass is actively growing before that first late-spring fertilizer application.
Summer Maintenance
During summer heat, your lawn may experience stress. Raise your mower height to 3.5-4 inches to shade the soil and conserve moisture. Water deeply but infrequently, about 1 inch per week, including rainfall. This is when a slow-release fertilizer from your spring or early summer feeding is still providing support.
Fall Preparation
The fall fertilizer is key. Continue mowing as long as the grass grows. Keep leaves raked to prevent smothering the turf. This is also a good time to aerate if your soil is compacted, which helps the fertilizer reach the roots.
Winter Dormancy
Do not fertilize during dormancy. The grass cannot use the nutrients, and they will likely leach away or pollute groundwater. Focus on keeping the lawn clear of debris and avoiding heavy traffic on frozen grass.
Troubleshooting Common Fertilizer Problems
Even with good intentions, issues can arise. Here’s how to identify and fix them.
Fertilizer Burn
This appears as yellow or brown streaks or patches shortly after application, often following spreader lines or where granules were spilled.
- Cause: Over-application, using quick-release fertilizer in high heat, or failing to water it in properly.
- Fix: Water the area deeply and daily for a week to flush excess salts from the soil. The grass may recover if the crowns (growth points) are not killed.
Excessive Thatch Buildup
While fertilization promotes growth, overdoing it, especially with quick-release nitrogen, can cause grass to grow too fast, leading to a thick layer of undecomposed organic matter (thatch) between the soil and grass.
- Prevention: Use slow-release fertilizers and ensure proper mowing and watering practices.
- Solution: Dethatch your lawn if the layer exceeds 1/2 inch thick.
Nutrient Runoff And Pollution
Excess fertilizer, particularly phosphorus, can wash into storm drains and waterways, causing algal blooms and ecological damage.
- Prevention: Follow soil test recommendations, use slow-release products, avoid application before rain, and keep fertilizer off hardscapes.
Frequently Asked Questions
Can I Fertilize St Augustine In The Summer?
Yes, but with caution. A light application of a slow-release fertilizer in early summer is acceptable. Avoid fertilizing during periods of extreme heat or drought stress, as the grass may not be able to process the nutrients effectively and the risk of burn increases.
What Is The Best Month To Fertilize St Augustine In Florida?
In Florida, the growing season is long. The first application is often in March or April, with follow-ups in June, September, and sometimes a light feeding in November for South Florida. Always adjust based on your specific grass condition and local advisories.
How Often Should You Fertilize St Augustine Grass?
For a maintained lawn, 2 to 4 times per year is standard. Twice (late spring and early fall) is often sufficient for healthy soil. Three times (spring, early summer, fall) is common. Four times is usually only for lawns in very warm climates or with sandy soil that doesn’t hold nutrients well.
Is It Too Late To Fertilize St Augustine In October?
In most regions, yes, it is too late. Fertilizing this late can stimulate new growth that will be vulnerable to frost damage. The last feeding should be completed by late September at the latest, or at least 6-8 weeks before your average first frost date.
Should You Water St Augustine After Fertilizing?
Absolutely. Watering immediately after applying granular fertilizer is a critical step. Use about 1/4 to 1/2 inch of water to wash the granules off the grass blades and into the soil. This prevents leaf burn and starts the nutrient release process.
Mastering when to fertilize St Augustine grass sets the foundation for a resilient and attractive lawn. By aligning your feeding schedule with the grass’s natural rhythm, choosing quality slow-release products based on a soil test, and applying them with care, you provide exactly what your lawn needs to thrive. Consistency in this practice, combined with proper mowing and watering, will yield a dense, green turf that is the envy of the neighborhood and a joy for your family.