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Blossom End Rot

A physiological disorder — not a disease — that causes the bottom of fruits to turn dark, sunken, and leathery. Most common in tomatoes, peppers, courgettes, and aubergines.

Symptoms

  • check_circleDark, sunken, water-soaked patch at the blossom end of fruit
  • check_circlePatch turning brown or black and leathery as it dries
  • check_circleAffects developing fruits, not the whole plant
  • check_circleHealthy-looking foliage despite affected fruit

Causes

  • arrow_rightCalcium deficiency in the developing fruit
  • arrow_rightInconsistent watering disrupting calcium uptake
  • arrow_rightOver-fertilising with nitrogen or potassium blocking calcium
  • arrow_rightRoot damage from over-cultivation near the plant
  • arrow_rightWaterlogged or compacted soil limiting root function

How to Diagnose

The distinctive dark sunken patch at the base of fruits is the key sign. Soil calcium is rarely actually low — the problem is usually that the plant cannot take it up fast enough due to irregular watering.

Treatment

Remove affected fruits. Foliar spray with calcium chloride solution can help in the short term. Most importantly, stabilise watering to ensure consistent calcium delivery to developing fruits.

Prevention

Water deeply and consistently. Mulch to retain moisture. Avoid excess nitrogen. Do not disturb roots during the growing season. Add lime to acidic soils before planting.