Ammonium Sulfate Fertilizer 21-0-0
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Ammonium Sulfate Fertilizer 21-0-0
Fast-acting nitrogen and sulfur fertilizer for lawns, vegetables, and acid-loving plants. 100% water-soluble formula delivers rapid green-up while gradually acidifying alkaline soils — ideal for blueberries, azaleas, and rhododendrons.
Ideal Applications
FEATURES
🌿 21% Ammonium Nitrogen
Delivers nitrogen as NH₄⁺ — the ammoniacal form preferred by blueberries and other acid-loving plants. Fast uptake drives visible green-up in 7–10 days.
🔬 24% Plant-Available Sulfur
Sulfate sulfur (SO₄²⁻) is immediately available for protein synthesis, chlorophyll formation, and enzyme activation — one of the highest sulfur concentrations available in a water-soluble fertilizer.
⚡ 100% Water Soluble
Dissolves completely with no residue, making it ideal for soil drench, fertigation, and drip irrigation. No clogging, no guesswork.
🫐 Acidifying Action
Gradually lowers soil pH over time as ammonium converts to nitrate, releasing hydrogen ions. Creates and maintains the ideal acidic conditions for blueberries, azaleas, and camellias.
🌾 Dual-Purpose Formula
Provides both nitrogen and sulfur nutrition in a single application — no need for a separate sulfur supplement when both nutrients are deficient.
🧪 CDFA Registered
Registered with the California Department of Food and Agriculture (#2014005). Every batch meets state nutrient content standards for fertilizer quality.
🔭 Third-Party Lab Tested
Independently tested for heavy metal content. Results consistently meet EPA safety standards for garden and agricultural use. Certificate of Analysis available.
💧 Low Application Volume
High nutrient concentration means less product per application. A small amount delivers meaningful nitrogen and sulfur — cost-effective for large areas.
🏭 Made in the USA
Manufactured domestically under strict quality controls. Consistent purity and nutrient content in every bag, backed by our 90-day satisfaction guarantee.
🌱 Versatile Across Crops
Effective for lawns, vegetables, fruit trees, ornamentals, and houseplants. Works in soil, container, and hydroponic applications wherever nitrogen and sulfur are needed.
DERIVED FROM
Ammonium sulfate is a pure, single-compound fertilizer manufactured in the USA through a controlled industrial process. Each lot is tested for nutrient analysis and heavy metal content to meet CDFA registration requirements.
Primary Compound
Ammonium Sulfate — (NH₄)₂SO₄
Produced by reacting ammonia gas with sulfuric acid, forming a stable crystalline salt. This process ensures consistent purity, nutrient content, and solubility in every batch. Provides 21% nitrogen as ammonium (NH₄⁺) and 24% sulfur as sulfate (SO₄²⁻).
Nutrient Forms Delivered
Ammonium Nitrogen (NH₄⁺)
The ammoniacal form of nitrogen. Immediately available for plant uptake and particularly well-suited to acid-loving crops like blueberries that perform best with ammonium rather than nitrate nitrogen.
Sulfate Sulfur (SO₄²⁻)
The plant-available form of sulfur. Directly absorbed by roots without requiring microbial conversion. Supports chlorophyll production, protein synthesis, and enzyme function from first application.
SCIENCE BEHIND THE FORMULA
🌿 Nitrogen — 21%
Nitrogen is a core component of chlorophyll and amino acids. As ammonium (NH₄⁺), it drives rapid vegetative growth, deep green color, and recovery from chlorosis. Ammonium nitrogen is the preferred form for acid-loving plants.
⚪ Phosphorus — 0%
Not included. Use ammonium sulfate when your soil test shows adequate phosphorus. Pair with MAP 12-61-0 or Bone Meal 3-15-0 when phosphorus is also needed.
🍎 Potassium — 0%
Not included. For a complete program, pair with Potassium Sulfate 0-0-53 or MKP 0-52-34 when potassium is also deficient.
🔬 Sulfur — 24%
Sulfur is the fourth most important plant nutrient. As sulfate (SO₄²⁻), it is immediately plant-available and essential for chlorophyll production, protein synthesis, enzyme activation, and oil formation in crops.
Why Ammonium Nitrogen for Acid-Loving Plants?
Most fertilizers supply nitrogen as nitrate (NO₃⁻), which has an alkalizing effect in the root zone. Ammonium sulfate supplies nitrogen exclusively as ammonium (NH₄⁺). When soil bacteria convert ammonium to nitrate through nitrification, hydrogen ions (H⁺) are released — gradually lowering soil pH. This is precisely why ammonium sulfate is the preferred nitrogen source for blueberries, azaleas, rhododendrons, and camellias: it feeds plants while simultaneously creating the acidic conditions these crops require.
How Soil pH Changes Over Time
The acidifying effect of ammonium sulfate is gradual and cumulative. Expect 0.2–0.5 pH unit reduction per application season in most soils. Sandy soils with low buffering capacity acidify faster; clay soils and those with high organic matter respond more slowly. Always test soil pH before first application and retest every 4–6 weeks to track changes and prevent over-acidification.
| Plant Type | Target pH | AMS Benefit | Notes |
|---|---|---|---|
| Blueberries | 4.5–5.5 | Excellent | Creates ideal conditions; test every 6 months |
| Azaleas / Rhododendrons | 5.0–6.0 | Excellent | Maintains acidity in alkaline regions |
| Camellias | 5.5–6.5 | Good | Monitor — avoid dropping below 5.5 |
| Lawn Grass | 6.0–7.0 | Good | Provides N + slight acidification if needed |
| Vegetables | 6.0–6.8 | Good | Supplies nitrogen; monitor pH quarterly |
Ammonium Sulfate vs. Other Nitrogen Sources
| Feature | Ammonium Sulfate 21-0-0 | Urea 46-0-0 | Calcium Nitrate 15.5-0-0 |
|---|---|---|---|
| Nitrogen % | 21% | 46% | 15.5% |
| Nitrogen Form | NH₄⁺ (ammoniacal) | Urea → converts to NH₄⁺ | NO₃⁻ (nitrate) |
| Sulfur % | 24% | 0% | 0% |
| Secondary Nutrient | Sulfur 24% | None | Calcium 19% |
| pH Effect | Acidifying | Mildly acidifying | Alkalizing |
| Speed of Action | Fast (3–7 days) | Moderate (7–14 days) | Very fast (2–5 days) |
| Best For | Acid-loving plants, alkaline soils, sulfur deficiency | High-N needs, neutral soils | Calcium-deficient soils, fruiting crops |
| Burn Risk | Moderate — water in well | Low | Moderate |
Bottom line: Choose Ammonium Sulfate when you need both nitrogen and sulfur, or when lowering soil pH is beneficial. Choose Urea for maximum nitrogen concentration in neutral soils. Choose Calcium Nitrate when calcium is also needed or soil is already acidic.
APPLICATION RATES & DIRECTIONS
Always dissolve or water in thoroughly after application to prevent foliar burn and move nutrients into the root zone. Apply when temperatures are below 85°F to reduce volatilization risk.
Seasonal Timing Guide
Lawn Application
| Area | AMS Rate per Application | Actual N Provided | Frequency |
|---|---|---|---|
| Per 1,000 sq ft | 3–5 lb | 0.63–1.05 lb N | Every 4–6 weeks |
| Per Acre | 120–200 lb | 25–42 lb N | Based on soil test |
Vegetables
| Crop Type | Per 1,000 sq ft | Per Plant | Timing |
|---|---|---|---|
| Leafy Greens (lettuce, kale) | 1–2 lb | 1–2 tbsp | Every 3–4 weeks |
| Fruiting Crops (tomatoes, peppers) | 2–3 lb | 2–3 tbsp | At transplant, then at flowering |
| Root Crops (carrots, beets) | 1.5–2.5 lb | 1.5–2.5 tbsp | At planting only; avoid later apps |
Acid-Loving Plants
| Plant Type | Rate per Application | Frequency | Target pH |
|---|---|---|---|
| Blueberries (mature) | ¼–½ cup per bush | 2× per year (early spring + fall) | 4.5–5.5 |
| Azaleas / Rhododendrons | ¼ cup per foot of height | 2× per year | 5.0–6.0 |
| Camellias | ⅓ cup per plant | 2× per year | 5.5–6.5 |
| Hydrangeas (blue flowers) | ¼ cup per plant | Monthly during growing season | 5.2–5.5 |
Houseplants & Containers
| Container Size | Rate (dissolved in water) | Frequency |
|---|---|---|
| 4–6" pots | ½ tsp per gallon | Every 4–6 weeks during active growth |
| 8–10" pots | 1 tsp per gallon | Every 4–6 weeks |
| 12"+ pots | 1–2 tbsp per gallon | Every 4–6 weeks |
HOW TO USE
Soil Application (Granular)
- Calculate the required amount using the application rate tables or the calculator below.
- Spread evenly over the soil surface, keeping granules away from direct contact with stems and foliage.
- Sweep any granules off concrete, pavers, or stonework immediately — ammonium sulfate can cause rust-colored staining.
- Water thoroughly (at least ½ inch of irrigation) to dissolve granules and move nutrients into the root zone.
Liquid Application (Dissolved in Water)
- Measure the required amount per the rate tables above.
- Add to water and stir until fully dissolved — ammonium sulfate dissolves quickly at all temperatures.
- Apply to pre-moistened soil to prevent root burn. Never apply concentrated solution to dry soil.
- For fertigation systems: flush lines with plain water after application to prevent salt buildup.
Pro Tip: Blueberries & Acid-Loving Shrubs
For established blueberry bushes, apply ¼–½ cup per bush in early spring just as new growth begins, then again in early fall after harvest. Water in well and mulch with pine bark after each application to help maintain soil acidity. Test pH every 6 months — if pH drops below 4.5, skip the next application and retest.
When Ammonium Sulfate Is the Right Choice
- Soil is alkaline (pH above 6.5) and needs gradual acidification
- Growing acid-loving plants (blueberries, azaleas, rhododendrons, camellias)
- Both nitrogen and sulfur are deficient on a soil test
- Fertigation or drip irrigation system requires fully water-soluble inputs
- Fast nitrogen response is needed (visible in 7–10 days)
When to Consider Other Options
- Soil is already acidic (pH below 5.5) → Calcium Nitrate won't further lower pH
- You need the highest nitrogen concentration per dollar → Urea 46-0-0 provides more than double the N per pound
- Organic program required → Blood Meal 13-0-0 or Feather Meal 12-0-0 are OMRI-listed alternatives
- Extremely alkaline soils needing aggressive pH correction → Elemental Sulfur paired with ammonium sulfate acts faster
FERTILIZER CALCULATOR
SAFETY & HANDLING
Personal Protective Equipment (PPE)
- Wear chemical-resistant gloves when handling
- Use a dust mask or respirator in enclosed or poorly ventilated areas
- Safety glasses recommended when measuring or pouring
- Wash hands thoroughly with soap and water after handling
Storage Guidelines
- Store in a cool, dry location in the original sealed container
- Ammonium sulfate is hygroscopic — it will clump if exposed to humidity; keep tightly sealed
- Never store near or mix with urea — contact with moisture creates a cement-like mass
- Keep away from lime and other alkaline materials, which counteract the acidifying effect
- Store away from children and pets
- Properly stored, shelf life is indefinite
Application Precautions
- Avoid application when temperatures exceed 85°F to reduce burn risk
- Never apply to drought-stressed plants without watering first
- Keep off concrete, pavers, and stonework — rinse immediately if spilled to prevent rust staining
- Keep away from children and pets during and immediately after application
- Water thoroughly after every application to move nutrients into the root zone
- Avoid runoff into storm drains, water features, and waterways
First Aid
- Eye contact: Flush immediately with clean water for 15 minutes. Seek medical attention if irritation persists.
- Skin contact: Wash thoroughly with soap and water. Remove contaminated clothing.
- Ingestion: Do not induce vomiting. Rinse mouth and seek medical attention immediately.
- Inhalation: Move to fresh air. Seek medical attention if breathing difficulty persists.
Refer to the Safety Data Sheet (SDS) for complete safety and emergency information.
COMPLETE YOUR SYSTEM
Ammonium sulfate provides nitrogen and sulfur — build a complete nutrient program with these complementary products.
Add Phosphorus & Potassium
MAP 12-61-0
High-phosphorus water-soluble fertilizer for root establishment, flowering, and fruiting. Pairs well with ammonium sulfate in a complete N-P-K program.
Potassium Sulfate 0-0-53
Adds potassium and additional sulfur without changing soil pH. Ideal complement when potassium is also deficient in acid-loving plant programs.
MKP 0-52-34
Provides both phosphorus and potassium in one water-soluble formula. A clean, chloride-free option for sensitive crops and hydroponic systems.
Aggressive pH Correction
Alternative Nitrogen Sources
Urea 46-0-0
Higher nitrogen concentration for situations where sulfur is not needed or soil pH is already optimal. Cost-effective for large-scale N applications.
Calcium Nitrate 15.5-0-0
When calcium is deficient or soil is already acidic. Nitrate nitrogen with a pH-raising effect — the counterbalance to ammonium sulfate.
FREQUENTLY ASKED QUESTIONS
Have a specific question about rates, crops, or troubleshooting? Visit our dedicated Ammonium Sulfate FAQ page for answers covering blueberries, Zoysia, Bermuda grass, pomegranates, storage, and more.
What is ammonium sulfate and what does 21-0-0 mean?
Ammonium sulfate is a water-soluble inorganic salt — (NH₄)₂SO₄ — that provides 21% nitrogen as ammonium (NH₄⁺) and 24% sulfur as sulfate (SO₄²⁻). The 21-0-0 designation follows the standard NPK format: 21% nitrogen, 0% phosphorus, 0% potassium. The sulfur is not represented in the NPK numbers but is listed separately on the guaranteed analysis label. For a deeper look at how nitrogen forms differ, see our guide on the best nitrogen fertilizers.
Does ammonium sulfate lower soil pH? How much and how fast?
Yes, ammonium sulfate gradually acidifies soil over time. As soil bacteria convert ammonium (NH₄⁺) to nitrate (NO₃⁻) through nitrification, hydrogen ions (H⁺) are released, lowering soil pH. Expect 0.2–0.5 pH unit reduction per application season in most soils. Sandy soils respond faster; clay soils and those with high organic matter buffer change more slowly. Always test soil pH before first application and retest every 4–6 weeks to monitor progress and avoid over-acidification.
Is ammonium sulfate good for blueberries?
Yes — ammonium sulfate is one of the best nitrogen sources for blueberries for two reasons. First, blueberries strongly prefer ammonium (NH₄⁺) nitrogen over nitrate (NO₃⁻); nitrate can damage blueberries at normal application rates. Second, the acidifying effect of ammonium sulfate helps maintain the pH 4.5–5.5 range blueberries require. Apply ¼–½ cup per mature bush twice yearly (early spring and after harvest in fall), water in well, and test soil pH every 6 months. For a full berry fertilization guide, see What Is the Best Fertilizer for Berries?
How quickly does it work?
Very quickly. As a 100% water-soluble fertilizer, ammonium sulfate dissolves and becomes plant-available within 24–48 hours when watered in properly. Visible greening typically appears within 7–10 days. The nitrogen effect lasts 4–6 weeks before another application may be needed. The sulfur and pH-lowering effects accumulate over multiple applications and soil seasons.
Can I mix ammonium sulfate with other fertilizers?
Ammonium sulfate mixes well with most phosphorus and potassium fertilizers in solution. Avoid mixing with lime or other alkaline materials, which neutralize the acidifying effect. Critical: Never store or mix ammonium sulfate with urea — when these two contact moisture together, they form a hard, cement-like mass that is extremely difficult to break apart. Mix them fresh in solution only if your application requires both.
Is it safe for vegetable gardens and edible crops?
Yes, when used as directed. Our ammonium sulfate is independently tested for heavy metal content and meets EPA standards for agricultural use. Apply as a side-dress 4–6 inches from plant stems, water in thoroughly, and reduce or discontinue applications 2–3 weeks before harvest for leafy greens and fruiting vegetables.
Will it stain my concrete or pavement?
Yes, it can cause rust-colored staining on concrete, pavers, and stonework. If granules fall on hard surfaces, sweep or rinse them off immediately with plenty of water. To prevent staining, apply away from walkways and driveways, and water in promptly after application to dissolve any granules that land near paved areas.
What's the difference between ammonium sulfate and urea?
Both supply nitrogen, but they differ significantly. Ammonium sulfate (21-0-0) provides nitrogen immediately as ammonium, includes 24% sulfur, and has an acidifying effect on soil pH. Urea (46-0-0) contains more than double the nitrogen per pound but must first convert through soil bacteria before becoming plant-available, contains no sulfur, and has a milder acidifying effect. Choose ammonium sulfate when sulfur is needed or when lowering pH is a goal; choose urea when nitrogen concentration and cost-per-pound of N are the primary factors.
How should I store ammonium sulfate?
Store in a cool, dry location in the original sealed container. Ammonium sulfate is hygroscopic — it absorbs moisture from the air and will clump if left unsealed. Keep away from urea, lime, and alkaline materials. Properly stored, it has an indefinite shelf life. Keep out of reach of children and pets.
→ More questions? See the full Ammonium Sulfate FAQ page — covers Zoysia, Bermuda grass, pomegranates, foliar rates, pet safety, and more.
GROW WITH CONFIDENCE
Quality & Purity Standards
- CDFA Registered (#2014005) — meets California Department of Food and Agriculture nutrient content standards
- Third-party lab tested for heavy metal content — results consistently meet EPA safety standards
- Certificate of Analysis available for every production lot
- Packaged in our facility in Madera, California under strict quality controls
Hassle-Free Returns
Not satisfied with your results? Contact us within 90 days for a full refund — no questions asked. We stand behind every product we sell.
Environmental Responsibility
- No unnecessary fillers, binders, or additives — pure ammonium sulfate only
- High nutrient concentration means less product used per application, reducing packaging waste
- Manufactured domestically, reducing transportation impact
Charitable Contributions
A portion of Greenway Biotech's sales supports youth gardening and agricultural education programs in our community.
About Greenway Biotech, Inc.
Family-owned and operated since 1989 in Madera, California. For over 35 years, we've specialized in high-purity fertilizers and plant nutrition products — making gardens, and their humans, healthier.
DOCUMENTS
DISCOVER MORE
- Ammonium Sulfate Uses: Lawn, Garden & Soil Application — Complete guide to uses, application methods, food-grade uses, and when to choose ammonium sulfate vs. other nitrogen sources
- Best Nitrogen Fertilizer: The Top 7 Options Compared — Expert guide to choosing the right nitrogen source for your crop and soil type
- What Is the Best Fertilizer for Berries? — Nutrition and pH guide for blueberries, raspberries, and other acid-loving berry crops
HAVE QUESTIONS?
Check out our Ammonium Sulfate FAQ page for crop-specific rates, troubleshooting, and storage guidance — or contact our experts for personalized application advice.
📞 (562) 351-5168 | 📧 questions@greenwaybiotech.com | Mon–Fri 7AM–5PM PST
