Ammonium Sulfate Fertilizer 21-0-0 is a 100% water-soluble fertilizer that supplies 21% nitrogen as ammonium plus 24% sulfur as sulfate. Unlike most soluble fertilizers, which provide nitrogen as nitrate, ammonium sulfate delivers it entirely as ammonium — the form blueberries, azaleas, rhododendrons, and other acid-loving plants are adapted to take up.
Nitrogen drives vegetative growth and deep green color, and the 24% sulfur supports chlorophyll formation, protein synthesis, and enzyme function — so when a soil test shows both nutrients are low, one product addresses both. As soil bacteria convert the ammonium to nitrate, hydrogen ions are released and soil pH drops gradually, which makes ammonium sulfate well suited to alkaline soils and to crops that need an acidic root zone. It is a common choice for fast lawn green-up, blueberry and acid-loving ornamental feeding, sulfur-deficient soils, and fertigation, dissolving completely with no residue.
It is a fast-release soluble nitrogen source, so it should be watered in thoroughly after every application, kept off foliage and stems, and split across multiple passes rather than applied in one heavy dose to reduce turf burn risk. The acidifying effect is cumulative — test soil pH before the first application and retest periodically. It can leave rust-colored staining on concrete and stone, so keep granules off hard surfaces. Store sealed and dry, and never store it in contact with urea. CDFA registered and independently lab tested for heavy metals, with results consistently well below required limits.