Why does my lettuce bolt so quickly?
The heat and stress triggers that send lettuce to seed, and the sowing, siting and variety choices that give a summer-long supply.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 3 min
Short answer
Lettuce bolts in heat, in drought, and after any check to growth. Sow little and often in the cool of the year, provide light shade and steady moisture in summer, and switch to loose-leaf and cos types, which bolt far later than butterheads.
Lettuce is a cool-season crop that most people try to grow in July. Bolting is not a fault in the plant — it is exactly what lettuce does when the days get long and hot, and the answer is to work around it.
Step by step
- Recognise bolting early.The plant starts to elongate from the centre, the leaves become bitter and milky sap runs from cut stems. Once it starts, it does not stop.
- Sow little and often.A short row or a few modules every two or three weeks. A single big sowing means everything is ready at once and half of it bolts before you eat it.
- Avoid sowing in high summer heat.Lettuce seed will not germinate above about 25C. Sow in the evening, water the drill with cold water first, and shade the seedbed in July and August.
- Provide afternoon shade.Summer lettuce grown in the shade of taller crops, under fleece on hoops or behind a row of beans, lasts considerably longer before bolting.
- Keep moisture absolutely even.A dry spell is a check to growth and a check to growth triggers bolting. Mulch and water in the evening.
- Choose the right types for summer.Loose-leaf and cut-and-come-again varieties, and cos types, are far more bolt-resistant than butterheads and crispheads. Look for 'slow to bolt' on the packet.
- Do not let plants get root-bound in modules.A module-raised lettuce left too long before planting is checked, and often bolts within weeks of going out. Plant out young.
- Harvest as cut-and-come-again.Picking outer leaves rather than whole hearts extends the useful life of each plant considerably and sidesteps the problem.
- Use the shoulder seasons.March to May and August to October are the productive lettuce windows in the UK. Late summer sowings crop well into autumn under a cloche.
- Pull and compost bolted plants.They will not recover and they become bitter and inedible. Replace with a fresh sowing.
Tips
- Lettuce seed refuses to germinate in hot compost. Sow in the evening and shade the drill.
- Loose-leaf and cos varieties bolt far later than butterheads.
- Picking outer leaves instead of whole hearts doubles the useful life of every plant.
Common mistakes
- Sowing a whole packet in one go in May — Everything hearts up in the same fortnight and the rest bolts before you can eat it. Successional sowing every two to three weeks is the whole technique.
- Letting the bed dry out between waterings — Any check to growth is a bolting trigger. Even moisture matters more for lettuce than for almost any other salad crop.
If it doesn't work
Plants elongating from the centre
Cause: Bolting from heat or stress — Fix: Harvest what you can immediately; the leaves turn bitter within days.
Seed not germinating in July
Cause: Compost above 25C — Fix: Sow in the evening, water the drill cold first, and shade it. Or sow indoors somewhere cooler.
Bitter leaves before bolting is obvious
Cause: Heat or drought stress — Fix: Shade, mulch and water. Harvest in the morning when leaves are at their sweetest.
Plants bolt within weeks of planting out
Cause: Root-bound or checked transplants — Fix: Plant out young, and water thoroughly at planting.
Questions people ask
Can I stop lettuce bolting once it starts?
No. Once the flowering stem starts to extend, the leaves turn bitter within days and the process cannot be reversed. Harvest immediately or compost the plant.
Which lettuce is best for summer?
Loose-leaf and cut-and-come-again types, and cos varieties described as slow to bolt. Butterheads and crispheads are much quicker to run in heat.
Why will my lettuce seed not germinate in summer?
Lettuce seed goes dormant above about 25C. Sow in the evening into a drill watered with cold water, shade it, or start it somewhere cooler indoors.