What is magnesium sulfate monohydrate?

Magnesium sulfate monohydrate (MgSO4·H2O), known as kieserite, is a chloride-free magnesium–sulfur fertilizer carrying roughly 27% water-soluble MgO and 14% sulfur. Because its one water of crystallisation makes it only partially and slowly soluble, it feeds crops steadily through the growing season instead of washing away after the first rain.

Chemistry and typical specification

MgSO4·H2O contains one water of crystallisation (16.5% by mass), giving ~86% magnesium sulfate, about 27% water-soluble MgO (16% Mg) and 14–15% sulfur. It is sold as white powder or granules, is odourless, and is free of chlorides — a key difference from potassium chloride-based Mg sources.

Our granular kieserite is sized for blending and spreading; ask for the current TDS for lot-specific values.

Where monohydrate is the right choice

It excels in soil-applied nutrition on acidic, sandy or leaching-prone soils, in high-rainfall regions, and in chloride-sensitive crops (tobacco, potato, fruit trees, vegetables). It is a standard Mg component in NPK blends, oil-palm and plantation fertilizers, and in animal feed premixes where slow Mg release suits rumen physiology.

Choose it when magnesium must last in the soil; choose the heptahydrate when you need fully water-soluble magnesium for foliar or fertigation programs.

Packaging and supply

We supply magnesium sulfate monohydrate in 25/50 kg PP bags and 1000–1250 kg jumbo bags, with OEM and private-label packaging available. Moisture is controlled and each lot ships with a certificate of analysis.

For the fully soluble counterpart, see our magnesium sulfate heptahydrate (Epsom salt) page.