Fertilizer for St. Augustine Grass: NPK Guide and Application Rates
St. Augustine Grass is the most popular warm-season lawn grass in the southeastern United States, known for its thick, carpet-like growth and shade tolerance. It requires 2-4 pounds of nitrogen per 1,000 square feet annually. Iron supplementation is often needed to maintain dark green color without excessive nitrogen.
Quick Reference
What NPK Ratio is Best for St. Augustine Grass?
The recommended NPK ratio for st. augustine grass is 15-0-15. The nitrogen-forward 15-0-15 ratio drives leaf and stem development, which st. augustine grass need for photosynthesis and canopy growth.
St. Augustine Grass NPK needs shift at each growth stage. Starter fertilizer for new sod (St. Augustine is not typically seeded) during the Seedling phase, then n/a for lawn use once flowering begins.
NPK by Growth Stage for St. Augustine Grass
| Growth Stage | NPK Ratio | Notes |
|---|---|---|
| Seedling | 18N 24P 12K N 18% Nitrogen: leaf and stem growth P 24% Phosphorus: roots and flowers K 12% Potassium: health and disease resistance Learn more about NPK | Starter fertilizer for new sod (St. Augustine is not typically seeded) |
| Vegetative | 15N 0P 15K N 15% Nitrogen: leaf and stem growth P 0% Phosphorus: roots and flowers K 15% Potassium: health and disease resistance Learn more about NPK | Balanced nitrogen-potassium with no phosphorus for established lawns |
| Flowering | 15N 0P 15K N 15% Nitrogen: leaf and stem growth P 0% Phosphorus: roots and flowers K 15% Potassium: health and disease resistance Learn more about NPK | N/A for lawn use |
| Fruiting | 0N 0P 15K N 0% Nitrogen: leaf and stem growth P 0% Phosphorus: roots and flowers K 15% Potassium: health and disease resistance Learn more about NPK | Potassium-only winterizer for fall cold preparation |
When Should You Fertilize St. Augustine Grass?
In zone 8, start fertilizing st. augustine grass in April. In zone 11, begin as early as February. Apply every 8 weeks through the growing season.
Which Zones Can Grow St. Augustine Grass?
St. Augustine Grass grows in USDA zones 8 through 11, spanning a 4-zone range.
Fertilization Start by Zone
| Zone | Start Month |
|---|---|
| Zone 8 | April |
| Zone 9 | March |
| Zone 10 | March |
| Zone 11 | February |
What Are the Best Fertilizer Products for St. Augustine Grass?
Look for products with an NPK close to 15-0-15. Scotts Turf Builder Southern is the most popular choice among home gardeners for st. augustine grass.
- Scotts Turf Builder Southern
- Lesco 15-0-15
- Milorganite
- Pennington Ultragreen Southern
Prices vary by retailer and region. Check current pricing before purchasing.
Common Fertilizing Mistakes with St. Augustine Grass
- Applying too much nitrogen which promotes chinch bug and disease problems
- Using fertilizers with phosphorus when soil already has adequate levels
- Fertilizing during drought stress without adequate irrigation
- Applying nitrogen late in fall, increasing freeze susceptibility
- Not supplementing with iron and relying solely on nitrogen for color
Tips for Fertilizing St. Augustine Grass
- Apply 1 lb of nitrogen per 1,000 sq ft every 8 weeks during growing season
- Total annual nitrogen should be 2-4 lbs per 1,000 sq ft depending on your zone
- Apply iron (ferrous sulfate) for dark green color instead of more nitrogen
- Most Florida soils have adequate phosphorus; a 15-0-15 formula is often ideal
- Apply a potassium-only winterizer in October for cold tolerance
Organic Fertilizer Alternatives for St. Augustine Grass
Sources
Source:University of Florida IFAS ExtensionLast updated: