Bolting
The rapid shift from vegetative growth to flowering and seed production, usually triggered by heat, lengthening days, or stress. Leaf quality drops sharply once a plant bolts.
Bolting is the process by which a plant rapidly transitions from producing leaves, roots, or fruit to producing flowers and seeds. Once a plant bolts, the parts you want to eat change fast - lettuce turns bitter, spinach becomes tough and stringy, cilantro loses its characteristic leaf flavor and starts tasting like coriander seed. The plant is redirecting all available energy toward reproduction rather than the tissue you planted it for.
What Triggers Bolting
Most bolting is caused by one or a combination of three factors:
Heat. Lettuce, spinach, arugula, and cilantro are cool-season crops. When air temperatures consistently exceed 75-80°F, these plants interpret warmth as a deadline - summer is arriving, and they need to complete their lifecycle before it’s too late to set seed.
Day length (photoperiod). Many crops respond to lengthening days. As days exceed 12-14 hours of light, some plants receive a genetic signal to flower regardless of temperature. This is why cilantro bolts in late spring even in mild climates.
Stress. Drought, erratic watering, root disturbance from transplanting, or a sudden cold snap can all trigger bolting. The plant interprets stress as a survival threat and attempts to reproduce before conditions worsen.
Extending the Harvest
The most reliable method is timing. Cool-season crops should be planted in early spring (4-6 weeks before last frost) or in late summer for a fall harvest. The goal is to keep them growing through cool weather and harvest before the hot weeks that trigger bolting.
Bolt-resistant varieties exist for most cool-season crops. Look for labels like “slow-bolt,” “heat-tolerant,” or “summer crisp” in seed catalogs. These are bred to delay the photoperiod response, buying you extra weeks in warm conditions. ‘Jericho’ and ‘Flashy Trout’s Back’ romaines are notably slow to bolt; ‘Slow Bolt’ cilantro is the standard choice for warm-region growers.
Providing afternoon shade in warm climates - either from taller crops or shade cloth at 30-40% reduction - can extend the harvest window by 2-3 weeks.
Once a Plant Has Bolted
Removing flower stalks as soon as they appear can delay full senescence on herbs like basil and cilantro by a week or two. But once a plant has committed to flowering, the flavor change in leaves is difficult to reverse. Harvest what you can from the remaining lower leaves and pull the plant for composting.
For lettuce and spinach, bolted plants become nearly inedible quickly. Bitter compounds (particularly in lettuce) increase sharply after bolt initiation.
When Bolting Is the Goal
Bolting is only a problem when you want to eat leaves or roots. If you grow for seed saving, you need the plant to complete its full cycle. Bolted cilantro produces coriander seed. Bolted dill produces its distinctive seed heads used in pickling. Bolted arugula produces seeds that can be pressed for a peppery oil. In these cases, you want to encourage bolting and protect the seed heads from rain damage before harvest.