Magnesium Sulphate

Magnesium Sulphate (Epsom salts)

Magnesium Sulphate, also called Epsom salts, is a soluble salt that supplies magnesium and sulphur, 10.00% magnesium and 13.00% sulphur. It suits growers correcting a magnesium deficiency on flowering, fruiting or vegetable crops, as a foliar spray or through the soil.

At a glance

• Type: soluble mineral salt (amendment)
• Supplier certificate on file: BioGro licence 297. See the certificate and its dates.
• Analysis: magnesium 10.00%, sulphur 13.00%
• Use for: correcting magnesium deficiency on flowering, fruiting and vegetable crops
• Rate: foliar 110 g (6 tablespoons) per 10 litres of water once a month

What it is

Magnesium sulphate heptahydrate, the crystalline salt sold as Epsom salts. It dissolves fully in water, so it is quick acting as a soil drench or foliar spray and does not change soil pH.

What it does

• Magnesium is the atom at the centre of chlorophyll, so a shortage shows as yellowing between green veins on the older leaves first.
• Magnesium is also a cofactor for many plant enzymes, including those involved in energy transfer and sugar movement.
• The sulphate half supplies sulphur, used for proteins, oils and flavour compounds.
• Because it is fully soluble it corrects a deficiency faster than dolomite lime, which is the slow, pH raising magnesium source.

Analysis

• Sulphur (S) 13.00%
• Magnesium (Mg) 10.00%

How to use

• Foliar spray: 6 tablespoons (110 g) per 10 litres of water once a month.
• For more frequent use, cut the dose to 1.5 tablespoons (27 g) per 10 litres of water once a week.
• Spray with the lights off or in the cool of the day and wet both sides of the leaf.
• Magnesium competes with potassium and calcium for uptake, so adding magnesium a soil does not need can induce a potassium or calcium shortage. Yellowing between the veins has other causes too; confirm with a soil or leaf test before treating. Magnesium sulphate does not lift pH; if the soil is acid and short of magnesium, dolomite lime does both jobs.

Learn more in fifteen seconds

• Magnesium: what it does
• Sulphur: what it does
• Mulder's chart: what blocks what

Handling and storage

• Wear a mask to avoid inhaling particles and open in a well ventilated area.
• Wear gloves and eye protection, and wash hands after use.
• Once opened, keep sealed and dry.