Magnesium deficiency

Magnesium is needed to give leaves their green colour, so when there's a deficiency, yellow breaks through between the veins and around the leaf edges instead. Other colours, such as purple, brown or red, might also appear. Older leaves suffer first, and will die if they're not given any treatment. The nutrient can be leached out of light, sandy, acidic soil by high rainfall. Or if there is too much potassium in the soil, the plants absorb that instead of the magnesium.

Symptoms

The absence of magnesium is detected by yellowing between the leaf veins and around the leaf margins. Other colours might break through as the green fades.

Find it on

potatoes, apples, cherries, grape vines, tomatoes, camellias, rhododendrons