Magnesium deficiency

Magnesium (Mg) deficiency is a plant disorder with two main causes. Magnesium can be easily washed out of light soils in wet seasons or excessive potassium fertiliser usage can cause also Mg to become unavailable to the growing plant.

This disorder particularly affects potatoes, tomatoes, apples, currants and gooseberries, and chrysanthemums.

Symptoms include, yellowing between leaf veins, which stay green, givinga marbled appearance. This begins with older leaves and spreads to younger growth. Can be confused with virus, or natural aging in the case of tomato plants. Fruits are small and woody.

Mg deficiency can be rectified in the short term by applying a foliar feed fortnightly, with epsom salts diluted at a rate of 200g per 10 litres of water (8oz per 2½ gal). In the longer term add dolomitic limestone if soil pH allows, or other Mg containing rocks such as Kieserite. Reduce usage of potash fertilisers if this may be contributing to the problem.