Iron deficiency: how to recognise and treat it

Deficiency

Symptoms

Interveinal chlorosis — the youngest leaves at the shoot tips turn yellow while the veins stay green.
In severe cases leaves turn pale yellow or almost white, brown angular spots appear between the veins and leaf edges scorch.
Older, lower leaves stay green longer; yellowing that starts on old leaves points to another deficiency such as manganese or zinc.
Common on alkaline, limy, compacted or waterlogged soil, and in lime-hating plants watered with hard tap water.

Stop overwatering, especially in spring — overly wet soil brings on iron chlorosis.
Where a soil test shows no free lime, lower the pH gradually with sulfur products at the label rate.
For lime-hating pot plants, repot into ericaceous compost and water with rainwater.

Iron chelate as a soil treatment — EDDHA on soils above pH 7.5; EDTA or DTPA only on less alkaline soils, as they stop working above pH 7.2–7.5; follow the label rate.
For a quick but temporary green-up, spray leaves with iron chelate or iron sulfate in the evening or on a cloudy day; repeat as needed and follow the label, as too strong a spray burns leaves.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Test the soil pH and check for free lime before planting; on limy soil choose plants tolerant of high pH.
Do not over-water, and avoid compacting the soil.
Water lime-hating plants with rainwater rather than hard tap water, and do not overdo phosphate or other micronutrient fertilisers.

Figures checked against these sources.