Lack of magnesium manifests itself as yellow, brown or red patches between green veins on leaves, bringing the veins into relief like a green fishbone. Tomatoes, roses and chrysanthemums are most commonly affected, but this interveinal chlorosis may also be found on many other plants, including trees, shrubs, perennials, annuals, bulbs, fruit, vegetables and indoor plants. It is most likely to occur on soils that are acidic, after heavy rain or watering, or if there is a high level of potash in the soil.

Control

Treat affected plants with Epsom salts in autumn; either add neat to the soil, or dilute and spray onto foliage.