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Bolting

Bolting is when a plant prematurely produces a flower stalk and goes to seed, usually triggered by heat or day length. It makes herbs and leafy vegetables bitter and unusable.

Symptoms

  • check_circleTall central flower stalk appearing suddenly
  • check_circleLeaves becoming smaller and more pointed
  • check_circleBitter or tough flavour in leaves or stems
  • check_circlePlant putting energy into flowers rather than foliage

Causes

  • arrow_rightExposure to high temperatures above the plant's optimal range
  • arrow_rightLong days triggering photoperiod-sensitive plants
  • arrow_rightWater stress signalling the plant to reproduce
  • arrow_rightTransplant shock
  • arrow_rightCold snap followed by warmth (vernalisation)

How to Diagnose

If a herb or leafy vegetable suddenly sends up a tall central stem with small leaves and flowers, it has bolted. The remaining leaves will taste bitter.

Treatment

Once bolted, the plant cannot be reversed. Harvest any remaining usable leaves immediately. For some plants (basil, coriander), pinching off the flower stalk early can slow bolting and extend the harvest slightly.

Prevention

Grow bolt-resistant varieties. Sow at the right time of year to avoid heat stress. Keep soil consistently moist. Provide partial shade during the hottest part of summer. Harvest regularly to slow the plant's reproductive cycle.