Ammonium Sulfate Fertilizer 21-0-0
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Greenway Biotech · Made in California since 1989
Ammonium Sulfate 21-0-0.
Fast nitrogen. Real sulfur. Lower pH.
A 100% water-soluble fertilizer that delivers 21% nitrogen as ammonium plus 24% sulfur as sulfate — built for lawns that need a quick green-up, blueberries and other acid-loving plants, and high-pH soils that benefit from gradual acidification. CDFA registered and independently lab tested for heavy metals.
Find your size → Calculate how much I need21%
Nitrogen as fast-acting ammonium (NH₄⁺)
24%
Plant-available sulfur as sulfate (SO₄²⁻)
100%
Water soluble for soil drench and fertigation
35+yrs
Family-owned California fertilizer manufacturer
01 / Choose your size
Right-sized for the job.
Lawn coverage below assumes a high-maintenance turf rate of 5 lb per 1,000 sq ft per application (1.0 lb actual nitrogen). At a low-maintenance 2.5 lb rate, each bag covers roughly twice the area shown.
| Bag Size | Lawn Coverage (high-maint.) | Lawn Coverage (low-maint.) | Best For |
|---|---|---|---|
| 5 lb | ~1,000 sq ft | ~2,000 sq ft | Blueberry rows, raised beds, spot feeding |
| 25 lb | ~5,000 sq ft | ~10,000 sq ft | Most popular |
| 50 lb | ~10,000 sq ft | ~20,000 sq ft | Best value |
02 / Ideal applications
One bag.
Six different jobs.
Ammonium sulfate is most useful where fast nitrogen, sulfur nutrition, and gradual soil acidification work together.
Lawns & Turf
One of the most popular lawn nitrogen sources for fast green-up, especially on high-pH soils in alkaline regions. Apply 2.5–5 lb per 1,000 sq ft and water in.
Blueberries
The preferred nitrogen form for blueberries, which perform poorly on nitrate. Feeds the plant while helping maintain the acidic root zone it needs.
Azaleas & Camellias
Supports acid-loving ornamentals and helps hold soil pH in the target range. General horticultural guidance — confirm rates with a soil test.
Sulfur-Deficient Soils
Delivers 24% sulfate sulfur alongside nitrogen — useful when a soil test shows both nutrients are low and a single product can address them.
Fertigation & Drip
Dissolves completely with no residue, making it well suited to drip lines and fertigation. Flush lines with plain water after each application.
Vegetable Side-Dressing
A fast-release side-dress nitrogen source for heavy feeders. Confirm rates against a current soil test, and keep granules off foliage and stems.
03 / Why ammonium sulfate
Two nutrients.
One acidifying salt.
The case for ammonium sulfate comes down to nitrogen form, sulfur content, and what it does to soil pH over time.
NH₄⁺
Nitrogen in the form acid-loving plants want.
Most fertilizers supply nitrogen as nitrate. Ammonium sulfate supplies it exclusively as ammonium (NH₄⁺) — the form blueberries, azaleas, and rhododendrons are adapted to take up. For crops that struggle with nitrate, this is the more appropriate nitrogen source.
24%
Sulfur included, not sold separately.
Sulfur supports chlorophyll formation, protein synthesis, and enzyme function. Ammonium sulfate delivers it as immediately plant-available sulfate — so when a soil test shows both nitrogen and sulfur are low, a single product can address both.
pH↓
Gradual, cumulative acidification.
As soil bacteria convert ammonium to nitrate, hydrogen ions are released and soil pH drops gradually. Over a growing season of regular applications many soils show a measurable reduction — useful on alkaline soils, and the reason it pairs naturally with elemental sulfur for deeper pH correction.
100%
Fully soluble, no residue.
It dissolves completely in water, so it works as a soil drench, in fertigation, and through drip systems without clogging emitters. Because it is fast-release soluble nitrogen, watering in thoroughly after application is essential.
CDFA
Registered and lab-tested.
Every batch is registered with the California Department of Food and Agriculture and independently tested for heavy metals, with results consistently well below required limits for garden and agricultural use.
04 / The science
Why the ammonium form matters.
NH₄⁺
Ammoniacal nitrogen — (NH₄)₂SO₄
Nitrogen is a core component of chlorophyll and amino acids, and it drives vegetative growth and deep green color. Plants take it up in two main forms: nitrate (NO₃⁻) and ammonium (NH₄⁺). Most soluble fertilizers lean on nitrate, which has a mild alkalizing effect in the root zone. Ammonium sulfate supplies nitrogen entirely as ammonium.
That distinction is what makes the product behave the way it does. When soil bacteria convert ammonium to nitrate through nitrification, hydrogen ions are released — gradually lowering soil pH. This is why ammonium sulfate is a preferred nitrogen source for blueberries, azaleas, rhododendrons, and camellias: it feeds the plant while helping create the acidic conditions those crops require. The 24% sulfur arrives as sulfate, the plant-available form, absorbed directly by roots without microbial conversion.
The practical implication for the grower is timing and monitoring. The acidifying effect is gradual and cumulative, varying with soil texture, buffering capacity, and starting pH — sandy soils shift faster, clay and high-organic-matter soils more slowly. Test soil pH before the first application and retest periodically so acidification stays in the target range rather than overshooting.
For a deeper look at how nitrogen sources differ, see Best Nitrogen Fertilizer: The Top Options Compared.
05 / Application rates
Pick your use.
Get your rate.
Rates below are drawn from university extension guidance. Ammonium sulfate is fast-release soluble nitrogen — water in thoroughly after every application and keep granules off foliage.
Lawn & Turf
Quick answer: Apply 5 lb per 1,000 sq ft for high-maintenance turf (1.0 lb actual N), or 2.5 lb for low-maintenance turf (0.5 lb N). Split into 3–4 applications per year.
| Area / Maintenance Level | AMS Rate per Application | Actual N Provided | Source |
|---|---|---|---|
| High-maintenance turf — per 1,000 sq ft | 5 lb | 1.0 lb N | Clemson Ext.; UF/IFAS Ext. |
| Low-maintenance turf — per 1,000 sq ft | 2.5 lb | 0.5 lb N | Clemson Ext. |
| Warm-season grass coming out of dormancy | 3–4 lb | 0.6–0.8 lb N | Clemson Ext. |
⚠️ Soluble-Nitrogen Caution: Ammonium sulfate is 100% soluble (fast-release) nitrogen. UF/IFAS guidance recommends no more than 0.7 lb of soluble N per 1,000 sq ft in a single application — about 3.3 lb of ammonium sulfate. Split heavier annual totals across multiple passes to reduce turf burn risk.
Sources: Clemson University Cooperative Extension (turf fertilization); University of Florida IFAS Extension (urban turf fertilizer guidance).
Blueberries & Acid-Loving Plants
Quick answer: Apply roughly 2–3 oz per established blueberry bush (about ¼–⅓ cup), worked into a ring 12–18 inches out from the plant.
| Plant Type | Rate per Application | Frequency | Source |
|---|---|---|---|
| Blueberries (established, year 2+) | 2–3 oz per bush | 2× per year (spring + after harvest) | Univ. of Maryland Ext.; Univ. of Illinois Ext. |
| Blueberries (young, escalating schedule) | 2 oz rising to ~8 oz by maturity | Per Illinois Ext. age-based schedule | Univ. of Illinois Ext. |
| Azaleas / Rhododendrons | ~¼ cup per foot of height | 2× per year | General horticultural guidance |
| Camellias | ~⅓ cup per plant | 2× per year | General horticultural guidance |
Note: Blueberry rates are weight-based per University of Maryland and University of Illinois Extension. Azalea, camellia, and rhododendron rates are general horticultural guidance, not drawn from the same extension sources. Keep granules off foliage, water in thoroughly, and if soil pH drops below about 4.5, skip the next application and retest.
Sources: University of Maryland Extension (blueberry fertilization); University of Illinois Extension (blueberry age-based schedule).
Vegetable Side-Dressing
Quick answer: Side-dress 4–6 inches from the stem, water in, and confirm rates against a current soil test — vegetable nitrogen needs vary widely by crop.
| 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 |
📋 Soil Test First: Vegetable rates above are general side-dress guidelines and should be confirmed against a current soil test and your local cooperative extension service, as nitrogen needs vary significantly by crop, soil type, and growing conditions. Ammonium sulfate is a fast-release soluble nitrogen source — water in thoroughly and keep granules off foliage.
Sources: General horticultural side-dress guidance; not drawn from a specific extension publication. Confirm against your state cooperative extension service's vegetable production guide for crop-specific nitrogen rates.
Field & Acreage
Quick answer: About 239 lb of ammonium sulfate per acre delivers 50 lb of actual nitrogen; about 476 lb per acre delivers 100 lb N. Conversion: 1 lb actual N = 4.76 lb of product.
| Nitrogen Target | AMS Rate per Acre | Actual N Provided | Source |
|---|---|---|---|
| Moderate soil-test target | ~239 lb/acre | 50 lb N | New Mexico State Univ. Ext. |
| Higher soil-test target | ~476 lb/acre | 100 lb N | Oregon State Univ. Ext. |
📋 Soil Test First: Field crop application rates above are general guidelines based on typical soil-test levels and crop nitrogen-removal estimates. Actual rates should be confirmed by a current soil test and consultation with your local cooperative extension service, as needs vary significantly by soil type, crop variety, and regional conditions.
Sources: New Mexico State University Extension (nitrogen worked examples); Oregon State University Extension (per-acre nitrogen conversion).
06 / How to use & calculate
Measure.
Water in.
Watch it green.
Ammonium sulfate works fast when applied correctly — and the calculator below turns your area into an exact amount and the right bag size.
-
01
Calculate your amount
Use the calculator to convert your lawn area, garden size, or plant count into an exact quantity. Apply when temperatures are below 85°F to reduce volatilization risk.
-
02
Spread evenly, off foliage
Spread granules evenly over the soil surface, keeping them away from direct contact with stems and leaves. Sweep stray granules off concrete and pavers immediately — ammonium sulfate can cause rust-colored staining.
-
03
Water in thoroughly
Apply at least half an inch of irrigation to dissolve granules and move nutrients into the root zone. For fertigation, flush lines with plain water afterward to prevent salt buildup.
-
04
Test pH if used repeatedly
Because ammonium sulfate acidifies soil over time, test pH before the first application and retest every 4–6 weeks during repeated use. If pH drops below your target range, skip the next application and retest.
07 / Compare
Three nitrogen sources.
Different jobs.
Ammonium sulfate is not the highest-nitrogen option — it is the right one when sulfur, the ammonium form, or soil acidification matters. See Best Nitrogen Fertilizer for the full comparison.
| Product | Nitrogen | Secondary Nutrient | pH Effect | Best For |
|---|---|---|---|---|
| Ammonium Sulfate 21-0-0 (this product) | 21% as ammonium | 24% sulfur | Acidifying | Acid-loving plants, alkaline soils, sulfur deficiency |
| Urea 46-0-0 | 46% (converts to ammonium) | None | Mildly acidifying | Maximum nitrogen per pound, neutral soils, large areas |
| Calcium Nitrate 15.5-0-0 | 15.5% as nitrate | 19% calcium | Alkalizing | Calcium-deficient soils, fruiting crops, hydroponics |
| Potassium Sulfate 0-0-53 | None | 17% sulfur | Near-neutral | Adding potassium and sulfur without changing soil pH |
08 / Decision
Is this the right
nitrogen source for you?
Ammonium sulfate is a specialist's nitrogen source. Here is where it fits — and where another product serves you better.
Best Choice For
- Soil is alkaline (pH above 6.5) and would benefit from gradual acidification
- Growing acid-loving plants — blueberries, azaleas, rhododendrons, camellias
- A soil test shows both nitrogen and sulfur are deficient
- You need fast nitrogen response, with visible green-up in days rather than weeks
- Fertigation or drip irrigation requires a fully water-soluble input
- You want the ammonium form of nitrogen specifically, not nitrate
Consider Another Product If
- Soil is already acidic (pH below 5.5) — try Calcium Nitrate 15.5-0-0 instead
- You need the most nitrogen per dollar — Urea 46-0-0 delivers more than double the N per pound
- You need phosphorus too — pair with MAP 12-61-0
- You are running a recirculating hydroponic system — Calcium Nitrate is the standard hydroponic nitrogen source
- You need aggressive, deeper pH correction — pair with Elemental Sulfur
09 / Build the program
Nitrogen and sulfur are a start.
These complete the program.
Ammonium sulfate supplies N and S only. Round out a full nutrient program with these complementary products.
Phosphate
MAP 12-61-0
High-phosphorus water-soluble fertilizer for root establishment, flowering, and fruiting — the phosphorus partner in a complete N-P-K program.
Potassium + SulfurPotassium Sulfate 0-0-53
Adds potassium and additional sulfur without changing soil pH — a clean potassium source for acid-loving plant programs.
pH CorrectionElemental Sulfur
For highly alkaline soils where faster or deeper pH reduction is needed. Use alongside ammonium sulfate for a multi-front acidification approach.
Calcium + Nitrate NCalcium 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.
10 / Safety & handling
Read this before
you spread.
Ammonium sulfate is a low-toxicity mineral salt, but a few handling and storage practices protect both you and your results.
- Wear chemical-resistant gloves when handling; use a dust mask in enclosed or poorly ventilated areas and safety glasses when measuring or pouring.
- Store in a cool, dry place in the original sealed container. Ammonium sulfate is hygroscopic and will clump if left unsealed — never store it in contact with urea, which forms a cement-like mass with moisture.
- Apply when temperatures are below 85°F, never to drought-stressed plants without watering first, and water in thoroughly after every application.
- Keep granules off concrete, pavers, and stonework — rinse immediately if spilled to prevent rust staining. Avoid runoff into storm drains and waterways.
- First aid — eyes: flush with water 15 minutes; skin: wash with soap and water; ingestion: do not induce vomiting, rinse mouth, seek medical attention; inhalation: move to fresh air. Refer to the SDS below for complete safety and emergency information.
11 / FAQ
Common questions.
Honest answers.
If your question isn't here, contact our team at questions@greenwaybiotech.com or see the full Ammonium Sulfate FAQ page.
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 part of the NPK numbers but is listed separately on the guaranteed analysis label. For how nitrogen forms differ, see our guide on the best nitrogen fertilizers.
Does ammonium sulfate lower soil pH, and how fast?
Yes — it gradually acidifies soil over time. As soil bacteria convert ammonium to nitrate through nitrification, hydrogen ions are released, lowering pH. Over a full growing season of regular applications many soils show a measurable reduction, though results vary with soil texture, buffering capacity, organic matter, and starting pH. Sandy soils respond faster; clay and high-organic-matter soils buffer change more slowly. Test soil pH before the first application and retest every 4–6 weeks to avoid over-acidification.
Is ammonium sulfate good for blueberries?
Yes — it is one of the preferred nitrogen sources for blueberries, for two reasons. Blueberries are poorly adapted to nitrate nitrogen and perform better when nitrogen is supplied as ammonium, and the acidifying effect helps maintain the acidic root zone they need. University of Maryland and University of Illinois Extension guidance points to roughly 2–3 oz per established bush, applied in a ring 12–18 inches from the plant, twice yearly. For a full berry fertilization guide, see What Is the Best Fertilizer for Berries?
How much ammonium sulfate do I use on my lawn?
University extension guidance points to 5 lb per 1,000 sq ft for high-maintenance turf (delivering 1.0 lb actual nitrogen) and 2.5 lb for low-maintenance turf (0.5 lb N). Because it is fast-release soluble nitrogen, UF/IFAS recommends no more than 0.7 lb of soluble N per 1,000 sq ft in a single pass — about 3.3 lb of product — so split heavier annual totals across 3–4 applications. Always water in thoroughly after applying.
How quickly does it work?
Quickly. As a 100% water-soluble fertilizer, ammonium sulfate becomes plant-available within 24–48 hours when watered in properly, with visible greening typically appearing within 7–10 days. The nitrogen effect lasts roughly 4–6 weeks before another application may be needed. The sulfur and pH-lowering effects accumulate over multiple applications and seasons.
What's the difference between ammonium sulfate and urea?
Both supply nitrogen, but they differ. 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 priority.
Can I mix ammonium sulfate with other fertilizers?
It mixes well with most phosphorus and potassium fertilizers in solution. Avoid mixing with lime or other alkaline materials, which neutralize the acidifying effect. Critically, avoid dry-blending or storing ammonium sulfate in contact with urea — together with moisture they form a hygroscopic mass that is difficult to separate. Never combine it in concentrate with calcium fertilizers; use separate stock tanks for calcium and sulfate sources, and jar-test unfamiliar tank combinations before large-scale application.
Will it stain my concrete or pavement?
It can cause rust-colored staining on concrete, pavers, and stonework. If granules land 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.
Is it safe for vegetable gardens and edible crops?
Yes, when used as directed. Our ammonium sulfate is independently tested for heavy metals, with results consistently well below required limits for garden and 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. Confirm rates against a current soil test.
Ready to feed?
Pick your bag. We'll ship it.
Ammonium Sulfate 21-0-0 ships in 5 lb, 25 lb, and 50 lb bags — free shipping on orders over $100, backed by our 90-day satisfaction guarantee. Not happy with your results? Contact us within 90 days for a full refund.
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