Iron is a trace element or micronutrient, needed by plants in small, but essential amounts. Some plants, particularly lime-hating, ericaceous plants are more susceptible to shortages of iron in the soil or its unavailability.
Although a trace element, iron can be locked up in the soil, so the roots of azaleas, rhododendrons, camellias and other lime-hating, ericaceous plants cannot absorb it. Raspberries can also show similar signs of iron deficiency.
Leaves turn pale yellow between the veins.
Always plant lime-hating plants in acidic or neutral soil.
Feed plants with a special ericaceous plant food that contains sequestered or chelated iron that is more easily absorbed by plant roots.