21-0-0 Fertilizer
Nitrogen onlyAlso known as: Ammonium sulfate
21-0-0 is 21% nitrogen, 0% phosphate and 0% potash by weight. To apply 1 lb of nitrogen per 1,000 sq ft, spread 4.76 lbs of product per 1,000 sq ft; a 50-lb bag covers about 10,500 sq ft at that rate.
What 21-0-0 Means
Nitrogen (N)
21%
10.5 lb per bag
Green color and growth
Phosphate (P₂O₅)
0%
0 lb per bag
Root growth, new seedlings
Potash (K₂O)
0%
0 lb per bag
Stress, drought and cold tolerance
Pounds shown are per 50-lb bag. The N:P:K ratio simplifies to 1:0:0. The remainder of the bag is carrier, filler, and secondary nutrients.
How Much 21-0-0 to Apply
Lawn feeding is measured in pounds of nutrient per 1,000 sq ft. Here's how much product hits each common target.
| Target | Product / 1,000 sq ft | Per acre | 50-lb bag covers | Delivers (N-P-K lb) |
|---|---|---|---|---|
| 0.25 lb N | 1.19 lb | 51.9 lb | 42,000 sq ft | 0.25-0-0 |
| 0.5 lb N | 2.38 lb | 104 lb | 21,000 sq ft | 0.5-0-0 |
| 0.75 lb N | 3.57 lb | 156 lb | 14,000 sq ft | 0.75-0-0 |
| 1 lb N | 4.76 lb | 207 lb | 10,500 sq ft | 1-0-0 |
What It's For
Ammonium sulfate supplies quick nitrogen plus about 24% sulfur, and it acidifies the soil slightly. Popular for spoon-feeding and for alkaline soils.
When to Use It
Spring and fall spoon-feeds, often every 2–4 weeks at a light rate. Many turf managers use it to push fall growth on cool-season grass.
Before You Spread It
- All of its nitrogen is quick-release unless the label says otherwise. Keep single applications at or under 0.5–0.75 lb N per 1,000 sq ft, skip it in summer heat on cool-season grass, and water it in.
- Its high salt index makes it more likely to burn than urea at the same nitrogen rate. Never apply to wet, drought-stressed or heat-stressed turf.
- Repeated use lowers soil pH over time. Worth a soil test every couple of years if it's your main nitrogen source.
21-0-0 Products in Our Catalog
21-0-0 Calculator
Enter your lawn size to get the total amount, or change the analysis to check a different bag.
Spread 4.76 lb per 1,000 sq ft, 23.81 lb for 5,000 sq ft (0.48 bags).
Delivers 1 lb N, 0 lb P₂O₅ and 0 lb K₂O per 1,000 sq ft. Never exceed the label rate.
Common Questions
How much 21-0-0 per 1,000 sq ft?
To deliver 1 lb of nitrogen per 1,000 sq ft, apply 4.76 lbs of 21-0-0 per 1,000 sq ft, or about 207 lbs per acre. Many applications use half that or less, and the product label rate always comes first.
What is 21-0-0 fertilizer used for?
Ammonium sulfate supplies quick nitrogen plus about 24% sulfur, and it acidifies the soil slightly. Popular for spoon-feeding and for alkaline soils.
When should I apply 21-0-0?
Spring and fall spoon-feeds, often every 2–4 weeks at a light rate. Many turf managers use it to push fall growth on cool-season grass.
What do the numbers 21-0-0 mean?
They're the percentages by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A 50-lb bag of 21-0-0 contains 10.5 lbs of nitrogen, 0 lbs of phosphate and 0 lbs of potash; the rest is carrier and other ingredients.
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