Bolting: Why Lettuce and Spinach Run to Seed
On this page
From salad to seed stalk
A lettuce that suddenly grows tall in the middle is switching from leaf growth to flowering, and its leaves turn bitter. Once it starts, it will not go back.
Heat, long days and stress
Heat and long days trigger bolting in lettuce, spinach and other cool-season greens. Stress that slows leaf growth adds to it, so a dry spell in a heatwave is the worst combination.
How to stop it
- Grow greens in the cooler parts of the year: spring and late summer into autumn.
- Keep the soil evenly moist.
- Give some shade in hot spells.
- Pick leaves often, and harvest the moment you see the centre stretching.
Swap crops for the hottest weeks
Sow your main lettuce and spinach crops either side of midsummer, and use the hottest weeks for crops that like heat. Late-summer sowings of hardy leaves carry on into autumn.
Related problems: seeds not germinating, yellow leaves, why plants are not growing. Or go back to all garden problems.
Bolting questions
Can I eat bolted lettuce?
It is safe, but the leaves turn bitter.
Can I stop it once it starts?
No. Harvest what you can and resow at a cooler time.
Regional notes
The problem is the same on both sides of the Atlantic; local advice and timing differ. Trusted local guides for this page:
- UK: RHS: Grow your own: June jobs; RHS: Grow your own: July jobs; RHS: Grow your own: August jobs. Timing in your area: the UK vegetable planting calendar.
- USA: Utah State University Extension: Leafy greens: physiological problems; University of Illinois Extension: Spring greens; Garden Organic: What to sow and plant in August. Timing in your area: the USA vegetable planting calendar.
- Canada: your provincial agriculture department, or Canadian university gardening services. Timing in your area: the Canada vegetable planting calendar.
More problems: all garden problems.
Sources and further reading
- Utah State University Extension: Leafy greens: physiological problems
- University of Illinois Extension: Spring greens
- RHS: Grow your own: June jobs
- RHS: Grow your own: July jobs
- RHS: Grow your own: August jobs
- Garden Organic: What to sow and plant in August
- Garden Organic: What to sow and plant in September
Facts on this page are summarised in our own words from the pages above; each is supported by at least two of them, or by one plus well-established growing science (noted in our research file). Every source was opened and checked on 23 October 2026.
Keep a garden record
Most problems come back to the same beds in the same weeks. A simple record of what grew where, and when trouble started, lets you get ahead of it next year. Sketch your beds in the free Vegetable Garden Layout Planner Tool, and keep sowing dates, problems and harvests in the Global Vegetable Garden Planner (printable PDF). Every crop we cover is in the vegetable growing guides.
Last reviewed:
Fix The Cause, Then Plan The Next Crop
Troubleshooting works best when you improve the growing conditions and record what changed for the next season.
Keep going
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.