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Blossom-end rot: how to recognise and treat it

Growing conditions

Blossom-end rot — Photo: A13ean, CC BY-SA 3.0, Wikimedia Commons

Symptoms

A water-soaked spot, like a small bruise, at the blossom end of the fruit (opposite the stalk) that grows into a dark brown to black, sunken, leathery patch.
The first fruits of the season are affected most often.
On peppers the spots can form on the sides of the fruit near the blossom end and look like sunscald.
Sometimes the skin looks sound but the flesh inside is discoloured and shrunken.

Organic treatment

Remove affected fruits — they will not recover; the aim is to protect the next fruits.
Keep the soil or compost evenly moist and never let it dry out; in hot weather pots and grow bags may need watering twice a day rather than once with a double amount.
Mulch the soil to hold moisture around the roots.
Only if a soil test shows low calcium, add lime or bonemeal, and recheck the pH because lime raises it.

Chemical treatment

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

Prevention

Water evenly through fruit set and hot spells; consider larger containers, border soil or automatic watering where regular watering is hard.
Do not over-fertilise; use nitrate rather than ammonium forms of nitrogen, and feed only onto moist soil.
Do not hoe or dig close to the plants and damage the roots.
Keep soil pH around 6.5 and ventilate greenhouses during the day.

Plants it affects

Sources

Figures checked against these sources.