Iron chlorosis
Young leaves turn yellow while the veins stay green, usually because alkaline soil stops the plant taking up iron.
Also known as: Iron deficiency, Interveinal chlorosis
Symptoms and identification
The newest leaves turn pale yellow or almost white between the veins, which remain a sharp green. In severe cases leaves are small and develop brown edges, and the plant stops growing.
Causes
Iron is present in most soils but is locked up when the soil is alkaline, waterlogged or very cold. Hard tap water and lime-rich soils make it worse, especially for acid-loving plants.
Organic treatment
Mulch with leaf mould or pine needles and add compost to slowly lower the pH. Spray leaves with a chelated iron solution for a fast green-up while the soil is corrected.
Prevention
Grow acid-loving plants in slightly acidic mix with leaf mould, compost or cocopeat. Water with rainwater where possible, and improve drainage.
Chemical treatment (use with care)
Apply chelated iron (Fe-EDDHA in alkaline soils) to the soil at the label rate, or a micronutrient mix containing iron.