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Calcium deficiency: how to recognise and treat it

Deficiency

Calcium deficiency — Photo: Zemxer, CC BY-SA 4.0, Wikimedia Commons

Symptoms

New growth suffers first — young leaves curl or get dead brown edges while older leaves stay green.
Growing tips and root tips die back and the plant is stunted.
In fruit it shows as blossom-end rot (tomato, pepper, aubergine, courgette) or bitter pit (apple, quince).
Tipburn on lettuce and cabbage leaves, stunted heart leaves in celery, cavity spots on carrots.

Organic treatment

Keep the soil or compost evenly moist — the usual cause is not lack of calcium in the soil but poor water flow carrying it to young tissue.
On acid soil, add agricultural lime aiming at about pH 6.5, unless the plants prefer acid soil.
Dig in organic matter so the soil holds water better.

Chemical treatment

In some crops, preventive sprays of calcium chloride on the tissue at risk reduce the problem; follow the label dose. They do not cure blossom-end rot, because sprayed calcium hardly reaches the fruit.

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

Prevention

Never let fruit and vegetable plants dry out; mulch to reduce water stress.
Avoid overfeeding with potassium- or nitrogen-rich fertilisers such as tomato feed.
Do not prune hard, and ventilate greenhouses where the air is very humid.
Test the soil pH and correct it if it is too acid.

Sources

Figures checked against these sources.