St Augustine grass is a warm-season turf that demands a specific nutritional profile to maintain its dense, carpet-like growth and deep blue-green color. Feed it the wrong ratio or apply at the wrong time, and you risk disease, thatch buildup, or a disappointing yellow cast.
I’m Mohammad Maruf — the founder and writer behind Gardening Beyond. I study soil science bulletins from land-grant universities, cross-reference fertilizer formulation data from dozens of manufacturers, and synthesize real-world reports from thousands of lawn owners to separate marketing noise from agronomic truth.
After examining soil science data and owner feedback across hundreds of lawns, the clear winner for best fertilizer for st augustine grass depends on your specific goals.
How To Choose The Best Fertilizer For St Augustine Grass
Selecting the right fertilizer for St Augustine means looking past flashy packaging and focusing on nitrogen source, potassium content, iron levels, and release mechanism. This grass is sensitive to certain formulations, so a few key decisions separate a thriving lawn from one that struggles.
Understand NPK Ratios for Warm-Season Turf
St Augustine grass performs best with a nitrogen-rich formula but requires moderate potassium for root strength and disease resistance. Phosphorus is usually unnecessary unless a soil test reveals a deficiency. Ratios like 29-0-3, 25-5-10, or 24-0-6 align well with the grass’s seasonal needs. Avoid high-phosphorus blends unless you are establishing a new lawn from sod or plugs.
Slow-Release vs Quick-Release Nitrogen
Slow-release nitrogen (coated urea, polymer-coated sulfur, or natural organics) provides steady feeding over 8 to 12 weeks, reducing the risk of growth surges that invite large patch fungus. Quick-release sources like ammonium sulfate or urea deliver fast green-up but can cause rapid top growth and increase mowing frequency. A blend of both offers immediate color plus sustained feeding.
Iron and Micronutrients Matter
St Augustine develops a deeper green when iron is included in the blend. Products with 2 to 3 percent iron help correct chlorosis without pushing excessive leaf growth. Potassium above 5 percent also improves heat and drought tolerance, which is critical during summer stress periods.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Eco Solutions 25-5-10 | Slow Release | Sustained feeding, pet-safe lawns | 25-5-10 NPK, 110-day release | Amazon |
| Yard Mastery 24-0-6 | Premium Flagship | Complete lawn health, large areas | 24-0-6 NPK, 3% iron, 45 lb | Amazon |
| Jonathan Green 29-0-3 | High Nitrogen | Deep greening, general maintenance | 29-0-3 NPK, 5,000 sq ft | Amazon |
| The Andersons 20-27-5 | Starter | New lawns, sod installation | 20-27-5 NPK, 1% iron | Amazon |
| Espoma Organic 9-0-0 | Organic | Organic lawns, gentle feeding | 9-0-0 NPK, Bio-tone formula | Amazon |
| Petramax Liquid 28-0-0 | Liquid Nitrogen | Fast green-up, liquid application | 28-0-0 NPK, 32 oz | Amazon |
| Scotts Healthy Plus | Disease Control | Disease prevention, stressed lawns | Fungicide + fertilizer, 4M sq ft | Amazon |
| Yard Mastery 7-0-20 | Summer Blend | Summer stress relief, heat tolerance | 7-0-20 NPK, 3% iron | Amazon |
| Gardenwise 13-13-13 | All Purpose | Gardens, shrubs, and lawn | 13-13-13 NPK, slow release | Amazon |
| Purely Organic 10-0-2 | Natural | Pet-safe, phosphate-free areas | 10-0-2 NPK, plant-based | Amazon |
| Supply Solutions Urea 46-0-0 | Synthetic Nitrogen | Nitrogen deficiency correction | 46-0-0 NPK, 5 lb granules | Amazon |
In‑Depth Reviews
1. Eco Solutions Slow Release 25-5-10
The 25-5-10 NPK ratio is one of the most balanced options for St Augustine grass that I have seen in the mid-premium segment. With 65 percent of the nitrogen in slow-release granular form, this fertilizer delivers consistent color and growth without the rapid flush that often triggers fungal pressure. The inclusion of sulphur and potassium from sulphate of potash adds a natural soil-conditioning benefit that synthetic-only blends lack.
Owner reports consistently highlight the extended feeding window — many users see results for the full 110 days advertised, which reduces the number of applications needed over a growing season. The 22-pound bag covers roughly 4,000 square feet per application, making it a practical choice for average-sized suburban lawns. Families with children and pets appreciate the safety profile when used according to directions.
From a research perspective, the dual-release mechanism (quick + slow nitrogen) aligns well with St Augustine’s preference for steady nutrition during active summer growth. The moderate potassium content at 10 percent supports root depth and drought tolerance without pushing excessive blade growth that invites thatch buildup.
What works
- Exceptional 110-day feeding duration reduces application frequency
- Pet and child safe when applied as directed
- Balanced NPK supports both color and root strength
What doesn’t
- Coverage per bag is modest compared to larger economy sizes
- Slow release means noticeable green-up takes longer than quick synthetic
2. Yard Mastery 24-0-6 Flagship Granular Fertilizer
Yard Mastery’s Flagship formula delivers 24 percent nitrogen with 24 percent slow-release, paired with 6 percent potassium and 3 percent iron. This combination is particularly effective for St Augustine grass because the high iron content intensifies the blue-green color without forcing excessive leaf elongation. The Bio-Nite technology further enhances nitrogen availability as soil temperatures rise.
At 45 pounds, the bag covers up to 15,000 square feet, making it one of the most cost-efficient premium options on the market for larger lawns. The granule size is consistent and spreads evenly through both drop and broadcast spreaders. Owner feedback frequently mentions uniform greening within 7 to 10 days, followed by sustained color for 8 to 10 weeks.
The zero-phosphorus formulation is ideal for established St Augustine lawns where soil phosphorus is already sufficient. The potassium at 6 percent provides meaningful drought and heat stress protection during peak summer, which is a critical factor for this grass type in southern climates.
What works
- Large bag covers substantial acreage at a strong per-square-foot value
- 3 percent iron delivers noticeable deep green color
- Slow-release nitrogen supports steady growth without surge
What doesn’t
- Heavy bag may be cumbersome for smaller yards
- Premium price point requires upfront investment
3. Jonathan Green Green-Up 29-0-3
Jonathan Green has a long-standing reputation in turf nutrition, and the Green-Up 29-0-3 formulation is a high-nitrogen workhorse for St Augustine. With 29 percent nitrogen and a small amount of potassium, this granular fertilizer is designed to deliver rapid greening and dense turf density during the active growing months. The 15-pound bag covers 5,000 square feet.
This product is best applied in late spring and early summer when St Augustine is entering its peak growth phase. The nitrogen content is high, so following the labeled rate is important to avoid excessive top growth that can increase mowing frequency and thatch accumulation. Many owner reports praise the dramatic color transformation within the first week.
The lack of phosphorus makes it suitable for established lawns where soil tests indicate adequate phosphorus levels. The potassium at 3 percent provides a modest stress buffer, though lawns under extreme heat may benefit from a supplemental potassium source during midsummer.
What works
- Very high nitrogen content drives fast, visible greening
- Trusted brand with consistent granule quality
- Phosphorus-free for established turf
What doesn’t
- High nitrogen requires careful scheduling to avoid disease
- Potassium level is modest for summer stress periods
4. The Andersons Premium New Lawn Starter 20-27-5
For establishing new St Augustine sod, plugs, or sprigs, The Andersons Starter 20-27-5 provides the phosphorus that young grass needs to develop a strong root system. The 27 percent phosphorus content supports rapid root initiation, while the 20 percent nitrogen fuels top growth. The inclusion of 1 percent iron helps new turf achieve a deeper green earlier than standard starter blends.
This 18-pound bag covers up to 5,000 square feet, and the granule formulation includes both quick- and slow-release nitrogen. The dual-release approach gives new grass an immediate nutrient boost followed by sustained feeding as the roots establish. Owner reviews on new sod installations frequently cite faster rooting and reduced transplant shock compared to generic starter fertilizers.
It is important to note that this is a specialty product for establishment phases, not a maintenance fertilizer. Once the St Augustine is fully rooted, switching to a lower-phosphorus maintenance blend is recommended to avoid phosphorus buildup in the soil.
What works
- High phosphorus content accelerates root development
- Dual-release nitrogen supports both immediate and sustained growth
- Iron additive improves early color
What doesn’t
- Not suitable for ongoing maintenance of established lawns
- Phosphorus may be restricted in some local regulations
5. Espoma Organic All Season Lawn Food 9-0-0
Espoma’s Organic Lawn Food is specifically labeled for St Augustine grass, making it one of the few organic granular products that explicitly list this turf type. The 9-0-0 analysis is gentle and relies on natural ingredients enhanced with Bio-tone, a proprietary blend of beneficial microbes that help break down organic matter in the soil. The 28-pound bag provides broad coverage across a full season.
This product shines for homeowners who prioritize soil biology and want to avoid synthetic chemicals. The slow-release nature of organic nitrogen means color response is gradual, but the long-term improvement in soil structure and microbial activity is a genuine benefit. Users with sandy soils report better moisture retention after several applications.
The 9-0-0 ratio is low in nitrogen compared to synthetic alternatives, so more frequent applications or higher rates may be needed to achieve the same color density. However, the non-burning formula makes it forgiving during hot weather, which is a real advantage for St Augustine lawns that are prone to fertilizer burn.
What works
- Approved for organic production; safe for soil biology
- Explicitly labeled for St Augustine grass
- Won’t burn turf even in high heat
What doesn’t
- Low nitrogen content requires more frequent applications
- Color response is slower compared to synthetic fertilizers
6. Petramax Liquid Nitrogen Fertilizer 28-0-0
Petramax Liquid Nitrogen 28-0-0 offers a unique 2-in-1 release technology with 70 percent quick-release nitrogen for fast green-up and 30 percent slow-release for sustained feeding between applications. The liquid format allows for precise application through hose-end sprayers or pump sprayers, and a single 32-ounce bottle can treat up to 12,800 square feet at maintenance rates.
This product is particularly useful for spot-treating nitrogen-deficient areas or giving St Augustine a rapid boost before a stress event. The high nitrogen content delivers visible greening within days, which makes it a favorite among homeowners who want quick results. The family-owned company offers solid USA-based customer support.
Liquid nitrogen products require careful mixing and even coverage to avoid streaking. The 28-0-0 ratio is potent, so following the dilution rates is critical. For St Augustine, using the maintenance rate of 5 ounces per gallon of water is safer than the higher correction rate, which could push growth too aggressively.
What works
- Fast-acting liquid format for quick color response
- Dual-release technology provides extended feeding
- Large coverage area per bottle
What doesn’t
- Liquid application requires careful measuring and even distribution
- High nitrogen concentration can burn if over-applied
7. Scotts Turf Builder Healthy Plus Lawn Food
Scotts Turf Builder Healthy Plus is a 2-in-1 product that combines lawn fertilizer with a broad-spectrum systemic fungicide. For St Augustine grass, which is highly susceptible to large patch, brown patch, and gray leaf spot, this dual-action approach is a practical way to feed the lawn while preventing disease before symptoms appear. The 13.7-pound bag covers 4,000 square feet.
The fungicide component controls 27 listed diseases, including brown patch and powdery mildew, which are common in St Augustine during humid summer conditions. The fertilizer base helps the grass recover from existing stress while building tolerance for future challenges. Owner reports from the southern states indicate strong results when applied preventatively before conditions turn favorable for disease.
This product works best as a preventive treatment applied when environmental conditions (warm nights, high humidity) align with disease risk. It is not a curative for active, severe outbreaks. The all-grass-type compatibility means it is safe for St Augustine when used as directed.
What works
- Integrated fungicide saves a separate application step
- Effective preventive control against common St Augustine diseases
- Helps grass recover from environmental stress
What doesn’t
- Not a curative product for active severe disease
- Fungicide component adds cost compared to plain fertilizer
8. Yard Mastery 7-0-20 Summer Lawn Stress Fertilizer
This summer-specific blend from Yard Mastery features a 7-0-20 ratio that is deliberately low in nitrogen and high in potassium, exactly what St Augustine needs during heat stress. The 20 percent potassium supports root function and water regulation, while the 3 percent iron maintains green color without pushing vulnerable new growth. The Bio-Nite additive improves nitrogen efficiency in warm soil.
The 18-pound bag covers 6,000 square feet, and the granular formulation is easy to apply with standard spreaders. This is a targeted product for midsummer application when traditional high-nitrogen fertilizers can trigger disease. Owners who use this in July and August report noticeably better lawn condition through heat waves compared to neighbors using standard summer nitrogen feeds.
St Augustine grass naturally slows growth during extreme heat, and forcing it with high nitrogen at that time invites large patch and other fungal issues. The 7-0-20 formula respects the grass’s natural cycle and provides the nutrients it actually needs during stress periods.
What works
- High potassium content improves heat and drought tolerance
- Low nitrogen reduces disease risk during summer
- Iron content maintains green color without forcing growth
What doesn’t
- Not suitable as a primary spring or fall fertilizer
- Seasonal specificity means it sits unused for part of the year
9. Gardenwise 13-13-13 Slow Release Fertilizer
Gardenwise 13-13-13 is a balanced all-purpose fertilizer that works for St Augustine grass as well as vegetable gardens, shrubs, and trees. The equal NPK ratio provides nitrogen for growth, phosphorus for root development, and potassium for stress tolerance. The slow-release granules feed for up to 8 weeks per application, reducing the overall number of treatments needed.
The fine granule size ensures good soil contact and even nutrient distribution. For St Augustine, this product works best as a general-purpose option when you are also feeding garden beds and want a single product for multiple areas. Owner feedback from mixed-use properties highlights the convenience of one bag serving lawn and garden needs.
The phosphorus content at 13 percent means it is best used on lawns where a soil test confirms phosphorus is needed, or for properties with thin, poor soils. For established St Augustine lawns with adequate phosphorus, a zero-phosphorus maintenance blend would be more appropriate long-term.
What works
- Versatile formula works for lawn and garden areas
- Slow-release granules provide 8 weeks of consistent feeding
- Fine granules ensure even distribution
What doesn’t
- Phosphorus content unnecessary for many established lawns
- Balanced ratio is not optimized specifically for St Augustine turf
10. Purely Organic Products Lawn Food 10-0-2
Purely Organic Lawn Food uses a plant-based formula derived from distillers grains and soy, with no manure, biosolids, or harsh chemicals. The 10-0-2 analysis provides a moderate nitrogen level with a small amount of potassium and zero phosphorus, making it compliant with phosphate-restricted municipalities. The 15-pound bag covers 3,000 square feet.
This product is designed to promote lush green turf without the risk of burning, and the organic composition means no re-entry restrictions after application — it is immediately safe for family and pets. The lack of phosphorus makes it suitable for established lawns in areas with phosphate bans. Owner reviews appreciate the pleasant natural smell compared to manure-based organics.
The 10-0-2 ratio is lower in nitrogen than many St Augustine fertilizers, so results may be more gradual. The organic matter content does contribute to soil health over repeated applications, which is a long-term benefit that synthetic products do not provide.
What works
- Plant-based formula with no manure or biosolids
- No re-entry restrictions; safe for pets and children
- Phosphorus-free for regulated areas
What doesn’t
- Lower nitrogen content requires more frequent application
- Coverage per bag is less than synthetic alternatives
11. Supply Solutions Urea 46-0-0 Nitrogen Fertilizer
Supply Solutions Urea 46-0-0 is a straight nitrogen fertilizer with the highest N concentration available. At 46 percent urea nitrogen, it is an economical way to correct nitrogen deficiency or push rapid green-up when used correctly. The 5-pound bag is a practical size for spot treatments or small lawns, and the fine granules dissolve readily when watered in.
Urea is the most concentrated dry nitrogen source, which means small amounts go a long way. For St Augustine, the recommended rate is approximately 0.2 pounds per 1,000 square feet for turf, which requires careful measuring to avoid over-application. This product is best used by experienced lawn owners who understand how to calibrate spreaders for high-analysis materials.
The primary risk with straight urea is volatility — if not watered in within 24 to 48 hours, some nitrogen can be lost as ammonia gas. St Augustine lawns with heavy thatch layers are especially prone to this loss. Despite these considerations, urea remains a cost-effective tool for targeted nitrogen supplementation when used with proper technique.
What works
- Highest nitrogen concentration available for rapid correction
- Very economical per pound of actual nitrogen
- Fine granules dissolve easily for quick uptake
What doesn’t
- Requires precise measuring to avoid burn or waste
- Volatile if not watered in promptly
- No potassium, iron, or secondary nutrients
Hardware & Specs Guide
NPK Ratio
The three-number ratio on fertilizer labels represents nitrogen (N), phosphorus (P), and potassium (K). For St Augustine grass, nitrogen drives blade growth and color, potassium supports root health and stress tolerance, and phosphorus is primarily needed during establishment. A typical maintenance ratio for St Augustine ranges from 3-0-2 to 4-0-3, meaning three to four parts nitrogen for every two to three parts potassium, with minimal phosphorus.
Nitrogen Release Mechanism
Fertilizers use either quick-release nitrogen (water-soluble, immediate green-up) or slow-release nitrogen (polymer-coated, sulfur-coated, or organic-based, feeding over weeks). Slow-release is generally safer for St Augustine because it avoids rapid growth flushes that can trigger fungal disease. Many premium products blend both types for immediate color plus sustained feeding.
Iron Content
Iron is a micronutrient that enhances chlorophyll production, resulting in a deeper green color without pushing excessive leaf growth. Products with 2 to 3 percent iron are especially beneficial for St Augustine, which naturally responds well to iron supplementation. Iron can also help correct yellowing caused by high soil pH or iron chlorosis.
Potassium for Stress Tolerance
Potassium (K) regulates water movement within the plant and strengthens cell walls, improving drought tolerance and disease resistance. For St Augustine, a potassium level of 5 to 10 percent in the bag is ideal during summer stress periods. Products like 7-0-20 or 24-0-6 with elevated potassium provide targeted support when the grass faces heat and humidity pressure.
FAQ
What is the best NPK ratio for St Augustine grass?
When should I fertilize St Augustine grass in the spring?
Can I use a weed-and-feed product on St Augustine?
Final Thoughts: The Verdict
For most gardeners, the best fertilizer for st augustine grass winner is the Eco Solutions Slow Release 25-5-10 because its balanced NPK, 110-day feeding window, and pet-safe formula cover the widest range of lawn needs. If you want premium iron-enhanced color and large-area coverage, grab the Yard Mastery 24-0-6 Flagship. And for summer stress protection, nothing beats the Yard Mastery 7-0-20 Stress Blend.