Bolting is when agricultural and horticultural crops prematurely produce a flowering stem (or stems) before the crop is harvested, in a natural attempt to produce seeds and hence reproduce. These flowering stems are usually vigorous extensions of existing leaf-bearing stems, and in order to produce them, a plant diverts resources away from producing the edible parts such as leaves or roots, resulting in a poor quality harvest from the grower's point of view. Plants that have produced flowering stems in this way are said to have bolted. Crops inclined to bolt include lettuce, beetroot, brassicas, spinach, celery and onion.
Bolting is induced by plant hormones of the gibberellin family, and can occur as a result of several factors, including changes in day length, the prevalence of low temperatures at particular stages in a plant's growth cycle, and the existence of stresses such as insufficient water or minerals. These factors may interact in a complex way. Day length may affect the propensity to bolt in that some plants are "long day plants", some are "short day plants" and some are "day neutral", so for example when a long day plant, such as spinach, experiences increasingly long days that reach a particular length, it will be inclined to bolt. Low temperatures can affect the propensity of some plants to bolt if they are experienced for sufficient periods at particular points in the life cycle of the plant; once these conditions have been met, plants that require such a trigger will subsequently bolt regardless of subsequent temperatures. Plants under stress may respond by bolting so that they can produce seeds before they die.
- Stefan Buczacki & Keith Harris (1998). Pests, Diseases & Disorders of Garden Plants. Collins. pp. 604–5. ISBN 0 00 220063 5.
- Zeevaart, J. A. D. (1971). "Effects of Photoperiod on Growth Rate and Endogenous Gibberellins in the Long-Day Rosette Plant Spinach". Plant Physiology 47 (6): 821–827. doi:10.1104/pp.47.6.821. PMC 396778. PMID 16657712.