Bolting is the term given to plants – but mostly vegetables – that flower and run to seed prematurely, before they’re ready to harvest. As the plant puts all its energy into the flowers and subsequent seed production, diverting it away from the parts you normally harvest, the crop is usually ruined or the quality, taste and yield are significantly reduced.
Bolting is brought on by sudden changes in temperature – both cold and hot – and widely fluctuating temperatures, plus changes of day length. It is also brought on when plants are under stress. Although the signs are only seen on crops that are approaching maturity, and ready to harvest, it is usually initiated in the plant much earlier.
Annual crops, such as lettuce, radish and spinach are long-day plants – they initiate flowers when the day length increases. It is natural for them to flower and run to seed as summer progresses, but this happens prematurely when the plants are stressed.
Biennial crops (which grow in the first year and then normally flower in the second) – including beetroot, carrots, leeks and onion – go to seed in their first year due to incorrect growing conditions, often brought on by a prolonged cold spell, cold nights, hot days, widely fluctuating temperatures and late frosts.
You can usually still harvest and eat crops that have bolted, but the flavour may not be as good as you would normally expect or it may be tougher and more stringy. In some, such as lettuces and spinach, the flavour may take on a slightly bitter taste. Root crops, such as onions, carrots and beetroot, won’t store very well, so use them straight away rather than storing them.
