Copper sulfate

Copper sulfate is most commonly supplied as the pentahydrate, blue crystals containing around 25% copper, though a less-hydrated monohydrate with higher copper content is also used. It is fully water-soluble and supplies copper together with sulfate-sulfur.

Chemical formula

CuSO₄·5H₂O (pentahydrate)

Copper content

About 25% in the pentahydrate; higher in the monohydrate

Sulfur content

Supplied alongside copper as sulfate

Dual use

Also a basis for copper fungicides such as Bordeaux mixture

Copper sulfate supplies copper, a micronutrient needed for enzyme systems, photosynthesis, and reproductive development, along with sulfate-sulfur. Copper is strongly held by soil organic matter, which is why deficiency is most common on peat and muck soils, and it moves little once bound.

• Copper is available on dissolving but is strongly bound by soil organic matter
• Deficiency is most common on peat, muck, and sandy soils
• Sulfate-sulfur is supplied alongside the copper

Copper sulfate is used to correct copper deficiency in crops such as cereals grown on organic soils, applied to soil or as a foliar spray. Because copper binds tightly and persists, a soil application can last for several seasons, and foliar sprays are used where a quick, controlled dose is preferred.

• Corrects copper deficiency, notably in cereals on peat and muck soils
• Soil applications can remain effective over several seasons
• Foliar sprays give a quick, controlled dose when needed

Copper is required only in very small amounts, and because it accumulates in soil and does not readily leach, repeated applications, including from copper fungicides, can build up to levels toxic to plants and soil organisms. Copper sulfate is also toxic to aquatic life, so runoff to water should be avoided.