Guaranteed Analysis
Nutrient Breakdown
N · Nitrogen21%
Provides 21% fast-acting ammoniacal nitrogen that fuels rapid leafy green growth, promotes chlorophyll production, and corrects nitrogen deficiency for visibly greener foliage within 7-10 days
P · Phosphorus0%
N/A — Contains no phosphorus. Ideal for soils already testing high in phosphorus or where phosphorus runoff restrictions apply
K · Potassium0%
N/A — Contains no potassium. Pair with a potassium source like 0-0-60 Potash if soil tests indicate a potassium deficiency
Derived from: Ammonium Sulfate (NH₄)₂SO₄ — also provides 24% Sulfur (S) as sulfate
Overview
What It Is
Ammonium sulfate is an inorganic salt with the chemical formula (NH₄)₂SO₄. It is produced by reacting ammonia with sulfuric acid, resulting in white to off-white crystalline granules that dissolve completely in water. The fertilizer contains two essential plant nutrients: nitrogen in the ammonium form (NH₄⁺) and sulfur in the sulfate form (SO₄²⁻), both of which are immediately available for plant uptake.
Gardeners and farmers choose ammonium sulfate for several key reasons. First, the ammoniacal nitrogen is non-leaching compared to nitrate forms, meaning it stays in the root zone longer in sandy or well-drained soils. Second, the sulfate sulfur is already in the oxidized form that plants can absorb without waiting for soil microbes to convert it. Third, the acidifying effect—as ammonium converts to nitrate through nitrification, hydrogen ions are released, gradually lowering soil pH by 0.2 to 0.5 units per season.
This pH-lowering property makes ammonium sulfate particularly valuable in regions with naturally alkaline or calcareous soils, where nutrients like iron, manganese, and zinc become less available at higher pH levels. By bringing the pH down, ammonium sulfate helps unlock these micronutrients, improving overall plant nutrition beyond just nitrogen and sulfur.
Crop Fit
Best For
BlueberriesAzaleasRhododendronsLawnsEvergreensPotatoesCornHydrangeas
Ammonium sulfate is the preferred nitrogen source for blueberries because they require ammonium nitrogen specifically and are sensitive to nitrate ions. Azaleas, rhododendrons, camellias, and hydrangeas all thrive in acidic conditions (pH 4.5-6.0) that ammonium sulfate helps create. For lawns, it produces rapid dark green color and is especially effective on alkaline soils. Potatoes and corn are heavy nitrogen feeders that respond well to the quick-release ammonium nitrogen. Evergreens benefit from both the nitrogen for needle growth and the soil acidification.
Application Rates
How Much to Use
| Garden & beds | 0.5 lbs per 100 sq ft for flowers, shrubs, and hedges; 1 lb per 100 sq ft for vegetable gardens |
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| Lawn | 3-5 lbs per 1,000 sq ft; up to 10 lbs per 1,000 sq ft for established turf with heavy nitrogen demand |
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| Trees & shrubs | 0.5 lbs per inch of trunk diameter, sprinkled evenly around the drip line |
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| Containers | 1 tablespoon per gallon of soil, mixed into the top 2 inches |
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| Frequency | Every 4-6 weeks during the growing season. Apply to established turf in early spring and again in late summer. |
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Step by Step
How to Apply
1Soil Test
Test your soil pH and nutrient levels before applying. Ammonium sulfate acidifies soil, which benefits acid-loving plants.
2Calculate Rate
Calculate the amount needed based on your area and the recommended application rate.
3Lawn Rate
For lawns, load a broadcast or drop spreader and apply 3–5 lbs per 1,000 sq ft evenly. Avoid overlapping.
4Garden Rate
For gardens, side-dress 1 tablespoon per plant or broadcast 0.5–1 lb per 100 sq ft for bed-wide application.
5Tree Rate
For trees, apply 0.5 lbs per inch of trunk diameter in a ring around the drip line.
6Water In
Water thoroughly immediately after application to move nutrients into the root zone and prevent leaf burn.
7Reapply
Reapply every 4–6 weeks during the growing season as needed. Monitor soil pH over time since repeated use lowers pH.
Begin by testing your soil to confirm nitrogen deficiency and check your current pH level. If your soil is already acidic (below pH 5.5), consider using a different nitrogen source like calcium nitrate instead. For broadcast application on lawns, calibrate your spreader to deliver 3-5 lbs per 1,000 sq ft and walk in overlapping passes for even coverage. Apply when the turf or foliage is dry to prevent leaf burn, and irrigate thoroughly immediately afterward. For vegetable gardens, side-dress by creating a shallow trench 4-6 inches from plant stems and sprinkling ammonium sulfate along the trench, then cover and water. For container plants, dissolve 1 tablespoon in a gallon of water and apply as a drench every 4-6 weeks. For foliar feeding, dissolve 1-2 tablespoons per gallon and spray in early morning or late afternoon to avoid leaf scorch. Never apply when temperatures exceed 85°F, and avoid top-dressing tomatoes, squash, watermelons, and beans directly.
Handling & Timing
Safety & Season
Safety & Storage
Wear gloves and eye protection during handling. Avoid inhaling dust during application. Store in a cool, dry location in a sealed container—ammonium sulfate is hygroscopic and will clump if exposed to humidity. Keep away from lime, urea, and alkaline materials. Do not apply near water sources, pools, or ponds to prevent contamination. Safe for use around pets and children once watered in and area has dried. Properly stored, it has an indefinite shelf life.
Seasonal Notes
Spring: Apply at green-up to kickstart growth on lawns and established perennials. Side-dress vegetable transplants 2-3 weeks after planting. Summer: Continue applications every 4-6 weeks on heavy-feeding crops like corn and potatoes. Avoid applying during extreme heat above 85°F. Fall: Apply to cool-season grasses in early fall for root development. Use on fruit trees and shrubs for shade and nut trees. Winter: Do not apply to dormant lawns or frozen ground.
In Context
How It Compares
Ammonium sulfate delivers 21% nitrogen compared to urea's 46%, meaning you need roughly twice as much product per unit of nitrogen. However, ammonium sulfate provides the added benefit of 24% sulfur and a soil-acidifying effect that urea lacks. Compared to ammonium nitrate (34-0-0), ammonium sulfate is safer to handle and store (non-explosive), though it delivers less nitrogen per pound. For acid-loving plants like blueberries, ammonium sulfate is the preferred choice over both urea and calcium nitrate because its ammonium nitrogen form is directly usable by these plants without risk of nitrate toxicity.
Answers
Frequently Asked Questions
What is ammonium sulfate 21-0-0 fertilizer?
Ammonium sulfate (21-0-0) is a nitrogen and sulfur fertilizer containing 21% nitrogen and 24% sulfur. It provides two essential nutrients in one application — nitrogen for vigorous green growth and sulfur for improved nutrient uptake and chlorophyll production. Unlike urea, ammonium sulfate also has a soil-acidifying effect, which makes it especially useful for acid-loving plants and alkaline soils that need pH adjustment. The nitrogen in ammonium sulfate is in the ammoniacal form, which is less prone to volatilization loss than urea. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 delivers dual-action nutrition for healthier, greener plants.
What is ammonium sulfate fertilizer used for?
Ammonium sulfate is used for crops and plants that need nitrogen supplementation along with sulfur, and for situations where soil acidification is desired. It is commonly applied to blueberries, azaleas, rhododendrons, and other acid-loving plants because it naturally lowers soil pH over time. It is also widely used on lawns, corn, wheat, and other agricultural crops that benefit from both nitrogen and sulfur. Because it provides sulfur, it helps correct sulfur deficiencies that can limit plant growth and yellowing. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 is versatile for garden, lawn, and farm applications.
Does ammonium sulfate lower soil pH?
Yes, ammonium sulfate has a significant soil-acidifying effect. As soil microbes convert the ammonium nitrogen to nitrate, hydrogen ions are released, which lowers soil pH over time. This makes ammonium sulfate an excellent choice for acid-loving plants like blueberries, azaleas, gardenias, and rhododendrons that require a pH of 4.5–5.5. It is also useful for correcting alkaline soil conditions that limit nutrient availability. The degree of pH change depends on soil type, buffering capacity, and application rate. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 provides nitrogen while naturally helping to maintain acidic soil conditions.
What is the difference between ammonium sulfate and urea?
Both are nitrogen fertilizers, but they differ in several important ways. Urea (46-0-0) contains more than twice the nitrogen per pound and is more economical for pure nitrogen delivery. Ammonium sulfate (21-0-0) provides 24% sulfur in addition to nitrogen and has a strong soil-acidifying effect. Urea is more prone to volatilization losses if not watered in quickly, while ammonium sulfate is more stable on the soil surface. Choose ammonium sulfate when you need sulfur or want to lower soil pH, and urea when maximum nitrogen per dollar is the priority. Old Cobblers Farm™ offers both options.
Is ammonium sulfate good for blueberries?
Yes, ammonium sulfate is one of the best nitrogen fertilizers for blueberries because it supplies nitrogen while simultaneously lowering soil pH — both of which blueberries require. Blueberries thrive at a soil pH of 4.5–5.5 and need consistent nitrogen for foliage and fruit production. Most other nitrogen fertilizers either raise pH or have no effect, but ammonium sulfate actively acidifies the soil with each application. Apply 2–4 ounces per plant for young bushes and 4–8 ounces for mature plants in early spring. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 is a top choice for blueberry growers.
How much ammonium sulfate per 1,000 square feet for lawns?
For lawns, apply 5–10 pounds of ammonium sulfate (21-0-0) per 1,000 square feet to deliver approximately 1–2 pounds of actual nitrogen. Apply in early spring or fall when grass is actively growing, and water thoroughly after application to prevent leaf burn. Ammonium sulfate works quickly and produces visible greening within days. It is particularly useful for lawns in alkaline soil regions where the acidifying effect helps improve nutrient availability in the root zone. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 provides fast-acting nitrogen with the added benefit of sulfur for healthier turf.
Can ammonium sulfate burn plants?
Like any concentrated nitrogen fertilizer, ammonium sulfate can burn plants if over-applied or placed in direct contact with stems and leaves. Always follow recommended application rates, keep granules away from plant crowns and stems, and water thoroughly after application to dissolve the fertilizer and move it into the root zone. When used correctly, ammonium sulfate is safe and effective for a wide range of plants. Splitting applications into smaller, more frequent doses reduces burn risk further. Old Cobblers Farm™ Wicked Growth Ammonium Sulfate 21-0-0 is easy to apply correctly when you follow the label guidelines.
