For the full breakdown, see our best Fall Fertilizer For St Augustine Grass guide.
St. Augustine grass needs steady feeding to stay dense, but too much nitrogen in one shot causes thatch buildup and disease pressure. Timing matters just as much as the numbers. The right schedule depends on where you live, but the safe pattern holds for most of the U.S.: wait for full green-up, feed with a slow-release turf fertilizer, and stop well before the lawn goes dormant.
Best Fertilizer Ratio And N-P-K Numbers
A 3-1-2 or 4-1-2 N-P-K ratio covers most St. Augustine lawns when you don’t have a soil test result. That means products like 12-4-8, 16-4-8, or 15-5-10. Nitrogen drives that green growth, potassium keeps roots and winter hardiness strong, and those low phosphorus numbers reduce runoff risk near waterways.
Slow-release nitrogen is the smart default. It feeds steadily over weeks rather than dumping everything at once, which cuts down on mowing peaks and repeated applications. If you overseeded with a cool-season grass like ryegrass, Harris County AgriLife recommends half a pound of nitrogen per 1,000 square feet in December and again in February using a straight nitrogen source like ammonium sulfate (21-0-0).
How Much Fertilizer Per Application
For actively growing turf, extension guidance consistently lands on 0.5–1.0 pound of actual nitrogen per 1,000 square feet per application. One heavy feeding of 2+ pounds causes a growth flush that invites brown patch and chinch bug problems.
Always check the bag’s label rate and calibrate your spreader — the numbers on the bag account for the exact analysis you bought.
When To Fertilize St. Augustine Grass
Start after green-up. That’s typically 2–3 weeks after the lawn turns green and frost risk has passed, which lands around April or May depending on your zone. Feeding before the grass is actively growing wastes product and feeds weeds. Your final application should happen by mid-September to mid-October in most regions so the grass hardens off before dormancy.
| Region | Annual Nitrogen Rate | Timing Notes |
|---|---|---|
| North Florida | 2–4 lb N per 1,000 sq ft | 2–6 applications, spring green-up through fall |
| Central Florida | 2–5 lb N per 1,000 sq ft | Florida rule caps single applications at 1 lb N |
| South Florida | 4–6 lb N per 1,000 sq ft | Longest growing season; watch waterway runoff |
| South Carolina | 2–4 lb N per 1,000 sq ft | Three summer feedings; extra potassium on clay |
| North Carolina | Up to 4 lb N per 1,000 sq ft | Feed in May; stop after mid-September |
| Texas / Harris County | 3–5 lb N per 1,000 sq ft | Every 6–10 weeks depending on release rate |
| Louisiana | ~3 lb N per 1,000 sq ft | April, June, optional August at 1 lb N each |
Regional guides differ because St. Augustine’s growing season stretches much longer in South Florida than in North Carolina. LSU’s schedule calls for April, June, and an optional August feeding at one pound each. Clemson recommends three summer feedings. NCSU says feed in May and hold off after mid-September. Texas lawns run longer, so feed every 6–8 weeks through the active months.
Common Fertilizer Mistakes To Avoid
The biggest error is feeding before green-up or during winter dormancy. December through February is off-limits unless you overseeded. The second mistake is overloading nitrogen at once — multiple light feedings beat one heavy dump, and
Skip the phosphorus unless a soil test says you need it. Florida and Texas guides lean hard on low- or zero-phosphorus blends, because runoff feeds algae in waterways. And when summer heat brings disease pressure, back off the high-nitrogen push entirely; a fall feeding with a higher-potassium product like 15-0-15 or 0-0-25 supports root health and winter survival without the disease risk of late-season nitrogen flushes.
Soil test first, slow-release nitrogen second, timing third. Stick to 0.5–1.0 pound of actual nitrogen per 1,000 square feet per application, never exceed the yearly cap for your region, and stop before dormancy. That routine builds the thick, weed-resistant St. Augustine lawn without the disease and thatch problems that come from overfeeding.
FAQs
What is the best N-P-K ratio for St. Augustine grass?
A 3-1-2 or 4-1-2 ratio, such as 12-4-8 or 16-4-8, works well for most lawns without a soil test. Products like 15-0-15 suit areas where phosphorus is unnecessary and potassium is a priority. A soil test remains the only way to know your exact needs.
When should I apply the first fertilizer of the year?
Wait until the grass has greened up and active growth has begun, typically 2–3 weeks after green-up. That usually falls in April or May for most regions. Fertilizing before green-up wastes product and feeds weeds before the turf can use it.
Can I fertilize St. Augustine in the fall?
Yes, a fall feeding supports root health and winter survival, but it should end by mid-September to mid-October in most regions. Use a lower-nitrogen, higher-potassium blend like 15-0-15 or 0-0-25 to avoid pushing tender growth that frost will damage.
References & Sources
- Texas A&M AgriLife Extension. “Maintaining St. Augustinegrass Lawns.” Details Texas feeding schedules, rates, and overseeding guidance.
- University of Florida IFAS. “St. Augustinegrass for Florida Lawns.” Outlines regional nitrogen rates and the single-application cap.
- Clemson Cooperative Extension. “St. Augustinegrass Maintenance Calendar.” Provides South Carolina feeding schedules and split-application guidance.