What is magnesium sulfate heptahydrate?

Magnesium sulfate heptahydrate (MgSO4·7H2O), commonly called Epsom salt, is a colourless crystalline salt that dissolves completely in water. With roughly 48.5% magnesium sulfate, about 16% water-soluble MgO and 12–13% sulfur, it is the fastest-acting magnesium source in agriculture and also serves feed, chemical and personal-care markets.

Chemistry and typical specification

The seven waters of crystallisation (51% by mass) make the salt fully water-soluble: our grade runs MgSO4 48.59%, water-soluble MgO 16.27%, pH 5–8 in solution, with crystal sizes from 0.1–4 mm plus a 2–4 mm granular cut. Purity of the salt itself is about 99.5% on a dry basis.

Each lot ships with a certificate of analysis; ask for the current TDS for up-to-date lot values.

Where heptahydrate is the right choice

Because it dissolves completely and quickly, it is the default magnesium source for foliar sprays (typically 1–2% solution), drip and sprinkler fertigation, hydroponics and seedling nutrition — correcting Mg deficiency within days rather than weeks. It is also widely used in animal feed, fermentation, textile dyeing, and as bath-salt and spa raw material.

For soil-applied, slow-release magnesium — especially on leaching soils or chloride-sensitive crops — the monohydrate (kieserite) is the more efficient choice.

Packaging and supply

We supply magnesium sulfate heptahydrate in 25/50 kg PP bags and 1000–1250 kg jumbo bags, with OEM and private-label packaging available. Store sealed — the salt is mildly hygroscopic and will cake if left open in humid conditions.

See our magnesium sulfate monohydrate page for the slow-release soil grade.