What is bolting?
Bolting describes an edible, frost-tolerant plant like lettuce, cilantro, or other greens quickly going to seed, before we would like. Signs that your plant might be bolting are when it gets taller than its maturity height and flower heads appear. In many cases, these changes make the vegetable flavor bitter, stems or roots woody, and, in general, unpalatable.
Why do plants bolt?
A rise in temperature, a cold period, changes in day length, or other plant stresses are factors that most often cause plants to bolt. When stress goes on long enough, plants switch their energy to survival of the species and therefore form flowers for reproduction, thus bolting.
How can bolting be prevented?
- Plant in the right season. Many cool-season or frost-tolerant crops like broccoli, lettuce, or radishes mature better before temperatures get into the 80s, so you'd have to plan accordingly. For example, if your springtime usually heats up quickly, start earlier, or plant in late summer, fall, or even winter, depending on your climate, when you have reliably cool weather. Also, certain crops, like winter radishes, will only form a nice root if they are planted in late summer or fall because the days get shorter.
- Avoid stress. Keep plants watered consistently. Transplant or transfer seedlings to a larger pot before the roots get crowded ("root bound") and remember to harden off plants before transplanting.
- Use row cover or plant in the shade of other plants to keep greens and lettuce cool as the season warms. Mulching a spring crop early can help keep the soil and roots cooler, prolonging the harvest.
- Cover young broccoli or cauliflower plants and near-mature bulbing onions during a cold snap to protect them from bolting. In the case of young broccoli and cauliflower, if young plants are stressed into flowering, the small plants will only produce small heads (which are actually un-opened flowers).
- Sow quick-maturing plants like lettuce, cilantro, or radish regularly. Succession sowing can keep some plants always coming into maturity instead of relying on one sowing to last a long time without bolting in the garden.
- Choose varieties that are "bolt resistant", "long standing", or are described as "holding well" or having a long harvest period. These varieties resist the environmental stresses that press them toward flowering.
- Try using seaweed or kelp liquid fertilizer, which are known to help plants handle stress better.