You plant a beautiful head of lettuce in May. By mid-June, before you've harvested more than a handful of leaves, the center shoots skyward and leaves turn bitter. This is bolting — one of the most frustrating events in a spring vegetable garden.
What Causes Bolting
Bolting is a plant's transition from vegetative growth to reproduction. Two primary triggers: day length and temperature. Most cool-season vegetables bolt when days exceed 14–16 hours or temperatures climb above their comfort range. Roots warming above 65–70°F can initiate bolting in lettuce even on a cool day.
Most Susceptible Vegetables
Lettuce — once the central stem elongates, bitterness is irreversible. See our edible gardening guides for growing conditions. Spinach — treat as spring and fall only; bolts quickly in heat. Cilantro — the window between usable herb and flowering plant can be 2–3 weeks; slow-bolt varieties like Calypso or Santo extend harvest by 2–3 weeks. Basil — regular pinching of flower buds is the primary management strategy.
How to Prevent or Slow Bolting
Timing is the first strategy — cool-season crops planted 4–6 weeks before last frost have more time before heat triggers bolting. "Slow bolt" varieties represent real genetic differences; Batavian-type lettuces hold weeks longer than butter or romaine in the same conditions. Shade cloth (30%) delays bolting by 1–3 weeks. For ideas on extending the kitchen growing season, visit our kitchen gardens resource. Sowing every 2–3 weeks so a new planting reaches harvestable size just as the previous one bolts is the most reliable overall strategy.
What to Do When Plants Bolt
Once the central stem elongates and flowers open, there is no reversal. Remove the plant and succession sow a summer-tolerant crop, or let it go to seed — cilantro produces coriander seed, and non-hybrid bolted plants can provide viable seed for next season.
Frequently Asked Questions
- Can I eat vegetables that have bolted?
- Bolted lettuce and spinach turn bitter — generally unpalatable raw. Bolted cilantro flowers attract beneficial insects and seeds become coriander. Bolted radishes develop edible seed pods.
- Does watering prevent bolting?
- Consistent moisture reduces heat stress and can slow bolting indirectly, but bolting is triggered by temperature and day length. Watering is a contributing factor, not a primary prevention strategy.
- Why does my cilantro bolt immediately after planting?
- Cilantro dislikes transplanting — root disturbance triggers early bolting. Always direct sow cilantro in place. Heat at planting time accelerates bolting; sow in early spring or late summer.
- Are there lettuces that don't bolt?
- No lettuce is immune, but Batavian types (Nevada, Sierra, Muir) hold the longest, extending the harvest season 4–6 weeks compared to standard varieties in the same conditions.
- Can I grow lettuce in summer at all?
- Heat-tolerant varieties under 30% shade cloth in afternoon shade can produce into early July in zones 5–6. Plan for a summer gap and restart cool-season varieties in August for fall.