A lack of magnesium in the soil, shows up as yellowing leaves on plants. This can affect their overall vigour and strength - as well as looking unsightly - so it's worth doing something about it.
Pale yellow areas develop, especially on foliage of fruit and vegetables. Tomatoes and rhododendrons are especially prone to show symptoms.
Pale yellow patches often tinged orange between leaf veins and around edges.
TREATMENT AND CONTROL
Epsom salts dissolved in water and sprayed onto foliage and applied around the roots will cure magnesium deficiency. In future, feed plants in spring with a balanced plant food that contains magnesium. For rhododendrons and azaleas, feed with a plant food specifically formulated for lime-hating or ericaceous plants. For roses, feed with a granular rose feed and for tomatoes, feed after the first truss has set with a liquid tomato feed.