St. Augustine grass has a notoriously low tolerance for nitrogen overload, yet it starves without a steady supply of it. The wrong high-nitrogen formula scorches its broad blades, while the right one turns your lawn into a dense, emerald carpet that chokes out weeds naturally.
I’m Mohammad Maruf — the founder and writer behind Gardening Beyond. I’ve spent years analyzing soil science data, comparing NPK release profiles, and studying aggregated owner feedback to help you match the right nitrogen source to your St. Augustine lawn’s unique stress points.
This guide breaks down the release mechanisms, iron boosters, and potassium balances that separate an effective feed from a costly mistake, so you can confidently choose the best high nitrogen fertilizer for st augustine grass and apply it without the guesswork.
How To Choose The Best High Nitrogen Fertilizer For St Augustine Grass
St. Augustine is a heavy feeder but a sensitive one. Selecting the wrong nitrogen source — too much fast-release or an unbalanced N-P-K — can cause rapid growth that attracts chinch bugs and large patch fungus. The following factors will guide you toward a formula that thickens the turf without inviting disease.
Nitrogen Release Mechanism
St. Augustine thrives on steady, consistent nutrition. Look for a fertilizer with a significant percentage of slow-release nitrogen (often labeled as polymer-coated or sulfur-coated). A 50% or higher slow-release content will feed the grass evenly over 6 to 12 weeks, preventing the surge-and-fade cycle that weakens root systems and encourages thatch buildup.
Potassium and Iron for Stress Resistance
While nitrogen drives blade growth, potassium (the third number in the N-P-K ratio) strengthens cell walls and improves drought tolerance. During hot Southern summers, a ratio like 24-0-11 or 24-0-6 ensures the grass can handle heat stress. Iron (Fe) is equally critical — a 2 to 3 percent iron content produces that signature deep blue-green color without forcing excessive leaf growth.
Phosphorus Sensitivity
Most established St. Augustine lawns do not need phosphorus. In fact, high phosphorus can trigger excessive runoff into waterways and, in some soils, interfere with micronutrient uptake. Choose a fertilizer with a zero middle number (like 27-0-5 or 24-0-6) unless a soil test specifically indicates a phosphorus deficiency.
Granules vs. Liquid Application
Granular fertilizers offer a measured, long-lasting feed and are less likely to cause leaf burn when watered in properly. Liquid formulations, such as a 28-0-0 concentrate, provide rapid green-up within days and are excellent for spot-treating nitrogen-deficient zones. However, liquids require more frequent reapplication and careful mixing to avoid scorching the grass blades under full sun.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| GreenView Fairway Formula 27-0-5 | Mid-Range | Steady 12-week feeding | 63% slow-release nitrogen | Amazon |
| Yard Mastery 24-0-6 (18 lb) | Mid-Range | Balanced iron + potassium | 3% iron, 6% potassium | Amazon |
| The Andersons PGF 16-0-8 | Mid-Range | Humic DG soil enhancement | Humic DG, dual-release N | Amazon |
| Petramax Liquid 28-0-0 | Mid-Range | Quick green-up correction | 70% quick, 30% slow release | Amazon |
| Yard Mastery 24-0-6 (45 lb) | Premium | Large lawn coverage | Covers 15,000 sq ft | Amazon |
| The Andersons Deep Green 24-0-11 | Premium | Heat stress prevention | 24-0-11, 2% iron + manga. | Amazon |
| SeedRanch St. Augustine 24-2-11 | Premium | St. Augustine-specific blend | 6% iron, 12,000 sq ft | Amazon |
In‑Depth Reviews
1. GreenView Fairway Formula 27-0-5 (33 lb)
The GreenView Fairway Formula starts with a 27-0-5 NPK ratio that delivers a strong nitrogen kick without the phosphorus that St. Augustine often doesn’t need. Its 63 percent slow-release nitrogen content spreads feeding across a full 12 weeks, preventing the green-up-then-fade pattern that leaves St. Augustine vulnerable to disease.
Each 33-pound bag covers 10,000 square feet, positioning it well for medium to large lawns. The small blue granules are designed to resist clumping and reduce the risk of overlap burn — a common issue when applying a high-nitrogen product on sensitive turf. Owners report visible greening within one week and consistent color with no surge spikes.
The phosphate-free formulation protects local waterways while still providing a complete nutrient profile. For the price per square foot, this bag delivers one of the longest feeding windows in its tier, making it a practical choice for homeowners who prefer fewer applications across the growing season.
What works
- Very high slow-release percentage minimizes burn risk
- 12-week feeding window reduces application frequency
- Phosphate-free formula is environmentally responsible
What doesn’t
- Low potassium content (5) provides less heat-stress support
- Blue granules may temporarily stain concrete if not swept
2. The Andersons Deep Green 24-0-11 (40 lb)
The Andersons Deep Green uses a 24-0-11 ratio that pairs high nitrogen with generous potassium — a combination St. Augustine needs during peak summer heat when lawn stress is highest. The 2 percent iron and manganese work together to boost chlorophyll production, intensifying blade color without forcing soft, disease-prone growth.
The super-fine particle design (the same Humic DG technology found in their PGF line) ensures uniform distribution across the lawn. Each 40-pound bag covers up to 10,000 square feet, and the dual quick-and slow-release nitrogen provides immediate color improvement followed by sustained feeding for up to eight weeks.
Owner reports consistently highlight dramatic recovery from brown spots within three weeks of application. The 11 potassium units are notably high for a St. Augustine fertilizer, giving this product an edge for lawns that face heavy foot traffic or extended dry spells during summer.
What works
- High potassium (11) boosts heat and drought tolerance
- Iron and manganese create deep, even greening
- Fine granule size reduces missed spots and streaks
What doesn’t
- Overlap creates very dark stripes that linger for weeks
- Premium price point is higher per bag than mid-range options
3. Yard Mastery 24-0-6 Flagship (45 lb)
The Yard Mastery Flagship formula in the 45-pound bag offers the best per-square-foot value in this guide while maintaining a professional-grade 24-0-6 NPK profile. The 24 percent slow-release nitrogen ensures the St. Augustine receives a steady diet rather than a feast-or-famine schedule, and the 3 percent iron delivers the deep blue-green color that St. Augustine owners prize.
Each bag covers 15,000 square feet, making it ideal for larger lawns that would require multiple bags of smaller products. The included Bio-Nite all-nutrient technology and micronutrient package — boron, copper, manganese, molybdenum, and zinc — addresses subtle deficiencies that granular nitrogen-only fertilizers often ignore.
Owners of Bermuda and St. Augustine alike report that one application thickens the lawn enough to choke out existing weeds. The growth stimulation is significant, so expect to increase mowing frequency to once or twice per week during the feeding period.
What works
- Exceptional coverage area for the bag weight and price
- Micronutrient package corrects hidden soil deficiencies
- High iron content produces rapid, deep color change
What doesn’t
- Growth surge may require twice-weekly mowing
- Not ideal for phosphorus-deficient soil (no phosphorus)
4. The Andersons PGF 16-0-8 with Humic DG (18 lb)
The Andersons PGF 16-0-8 takes a more moderate nitrogen approach (16 units) than some competitors, but the inclusion of Humic DG sets it apart. Humic acid improves soil structure and nutrient uptake efficiency, meaning the St. Augustine actually uses more of what you apply rather than letting it leach away.
The 8 percent potassium provides solid stress protection, and the super-fine particle size delivers twice the number of particles per square foot compared to standard granules. This reduces the risk of striping and ensures even coverage even when using a less precise spreader. Both quick-and slow-release nitrogen sources work together for an eight-week feeding window.
Soil-test-savvy owners typically switch to this product after discovering elevated phosphorus levels in their yard. The phosphorus-free formula lets them feed aggressively without compounding existing nutrient imbalances.
What works
- Humic DG improves soil nutrient efficiency over time
- Very fine particles prevent streaks and missed areas
- Phosphorus-free design suits high-phosphorus soils
What doesn’t
- Moderate 16 nitrogen may not satisfy heavy feeders
- Not available for purchase in California or Oregon
5. SeedRanch St. Augustine 24-2-11 (50 lb)
The SeedRanch blend is uniquely formulated for St. Augustine grass, with a 24-2-11 NPK ratio that includes a small amount of phosphorus (2) along with a significant 6 percent iron. The high iron content is the standout feature here — it produces the deepest green response of any product in this guide without requiring excessive nitrogen that could stress the turf.
Each 50-pound bag covers roughly 12,000 square feet, and the granular formulation flows well through standard broadcast spreaders. Owners of St. Augustine lawns in California and the Gulf states specifically praise this product for delivering consistent dark-green growth even during the transitional spring period when St. Augustine is waking up from dormancy.
The 11 units of potassium rival the Deep Green formula, giving this bag excellent heat-stress credentials. For homeowners who want a St. Augustine-specific blend rather than a general-purpose lawn feed, this is the most targeted option available.
What works
- St. Augustine-specific NPK formulation is uniquely targeted
- 6% iron delivers unmatched color depth
- Large 50 lb bag offers strong value for bigger lawns
What doesn’t
- Contains phosphorus which may not suit all soil types
- Bag weight is heavy for manual handling and spreading
6. Petramax Liquid Nitrogen Fertilizer 28-0-0 (1 Gallon)
Petramax 28-0-0 is a liquid nitrogen concentrate formulated with 70 percent quick-release and 30 percent slow-release technology. This dual-speed approach allows it to correct visible nitrogen deficiency within days while providing a residual feed between applications — a valuable trait for St. Augustine lawns that have yellowed unevenly.
One gallon mixed at the maintenance rate (5 ounces per gallon of water) covers up to 25,600 square feet, making it extremely efficient for spot-treatment or full-lawn application with a hose-end sprayer. The liquid form eliminates the granule distribution concerns that plague spreader-based feeding on uneven terrain or lawn slopes.
Owners who use the PetraTools sprayer system report the best results, as the integrated mixing instructions are calibrated for that hardware. The liquid route is best suited for homeowners who already have a sprayer and want the flexibility of correcting nitrogen levels mid-season without waiting for rain.
What works
- Ultra-high 28-0-0 nitrogen corrects deficiency rapidly
- Liquid application avoids spreader calibration issues
- Large coverage per gallon at maintenance rate
What doesn’t
- Requires a sprayer — no spreader application possible
- Frequent reapplication needed compared to granular options
7. Yard Mastery 24-0-6 Flagship (18 lb)
The 18-pound version of the Yard Mastery Flagship formula delivers the same 24-0-6 NPK and 3 percent iron content as the larger bag, but in a smaller format that suits lawns under 6,000 square feet. The 24 percent slow-release nitrogen feeds St. Augustine consistently, while the 6 percent potassium provides a meaningful stress buffer for summer heat.
This bag is an excellent entry point for homeowners who want to test a premium nitrogen formula before committing to a 45-pound investment. The micronutrient package — boron, copper, manganese, molybdenum, and zinc — mirrors the larger bag exactly, so there is no compromise in trace-element coverage.
User reports consistently note that Bermuda and St. Augustine lawns thicken enough to crowd out weeds after just one application. The growth response is vigorous, but the balanced potassium content helps prevent the weak, floppy growth that pure-nitrogen fertilizers can cause.
What works
- Same premium blend as the 45 lb bag in a smaller size
- Micronutrient package addresses trace deficiencies
- Good potassium level supports heat-stressed St. Augustine
What doesn’t
- Smaller bag may not be economical for larger lawns
- Significant growth flush requires more frequent mowing
Hardware & Specs Guide
Slow-Release Nitrogen Percentage
The percentage of nitrogen labeled as slow-release determines how long a single application feeds your St. Augustine. Products with 50 percent or more slow-release nitrogen, like the GreenView Fairway Formula at 63 percent, provide a 10- to 12-week feeding window and reduce the risk of foliar burn. A lower percentage (under 30 percent) means more frequent applications and a higher chance of growth surges during warm weather.
Potassium Content for Stress
Potassium (the third number in the N-P-K ratio) strengthens St. Augustine cell walls, improves drought tolerance, and helps the lawn resist large patch fungus. A potassium value of 8 to 11 is ideal for high-stress Southern climates. Products below 6 may leave the lawn vulnerable during July and August heat waves, especially on sandy soils where potassium leaches quickly.
Iron Concentration for Color
Iron (Fe) does not directly drive leaf growth, but it is the primary element responsible for deep green color. A fertilizer with 2 to 6 percent iron will produce visible color change within 7 to 14 days. Higher iron content (5 to 6 percent) is especially beneficial for St. Augustine grown in alkaline soils where iron availability is naturally low.
Coverage and Bag Weight
Bag weight and coverage area dictate how much product you need for your lawn. A 33-pound bag covering 10,000 square feet is a standard baseline. Larger bags (45 to 50 pounds) covering 12,000 to 15,000 square feet offer better value for bigger properties but are physically heavier to carry and load into a spreader. Always measure your lawn before buying to avoid over- or under-application.
FAQ
How often should I apply high nitrogen fertilizer to St. Augustine grass?
What happens if I use a fertilizer with too much fast-release nitrogen?
Should I use a liquid or granular high nitrogen fertilizer on St. Augustine?
Why is potassium important for St. Augustine grass in summer?
Can I use a high nitrogen fertilizer meant for Bermuda on St. Augustine?
Final Thoughts: The Verdict
For most gardeners, the best high nitrogen fertilizer for st augustine grass winner is the GreenView Fairway Formula 27-0-5 because it combines a 63 percent slow-release nitrogen profile with phosphorus-free safety and a 12-week feeding window that aligns perfectly with St. Augustine’s growth rhythm. If you want iron-driven color and maximum heat-stress protection, grab the The Andersons Deep Green 24-0-11. And for owners of large St. Augustine lawns seeking the best per-square-foot value, nothing beats the Yard Mastery Flagship 24-0-6 (45 lb).