Epsom salts (magnesium)

How it works

Magnesium sulphate corrects a genuine magnesium deficiency - and nothing else. Magnesium sits at the centre of every chlorophyll molecule.

Recipe

20 g per litre as a foliar spray, or 30 g per square metre watered in.

How to apply

Only when leaves show the specific sign: yellowing BETWEEN the veins on OLDER lower leaves, while the veins stay green. Common on sandy coastal soil and on tomatoes in pots.

Targets — pests

Not recorded — the field is blank rather than guessed.

Targets — diseases

Not recorded — the field is blank rather than guessed.

Supplies: Epsom salts

Days to harvest after spraying: 0

Best months: not recorded

Cautions

Not a general tonic. Excess magnesium competes with calcium uptake and can make blossom-end rot worse - the exact problem people often buy it to fix.

The thing people get wrong

Half the internet recommends Epsom salts for everything and it is wrong. If the yellowing is on the NEW top growth it is iron, not magnesium, and Epsom salts will make matters worse. Old leaves, between the veins, veins still green - that is the only picture that calls for it.