Lettuce before a hot spell

Highs of 85°F or more are forecast starting the forecast. Lettuce grows best in cool weather, and a run of hot days pushes many varieties to bolt (send up a flower stalk) and turn bitter.

When we suggest this

• ForecastHighs of about 85°F or more for 2 or more days in a row are forecast for today or the next 3 days.
• Your noteYour note: stage is growing or ready to harvest; or no stage noted yet.

What would stop us suggesting it

• When the forecast heat ends.
• When you mark it Done or Doesn't apply. "Doesn't fit my setup" stops it for that plant this season.

What to do

1. Before the forecast, pick the larger outer leaves and cut any heads that are full size.
2. During the hot days, check the soil and water if the top inch is dry.
3. If a plant starts to stretch up with a thick center stalk, it's bolting. Harvest it soon, before the leaves turn bitter.

What we can't know

• Whether your variety is slow to bolt. Some are sold as heat tolerant.
• How much afternoon shade the plants get.

Sources disagree on how much heat triggers bolting: several days above about 75°F (Minnesota), above about 80°F (Texas A&M), or around 85°F (Delaware). We use highs of 85°F or more on 2+ days to flag the clearest cases, so milder heat can still cause bolting. Long days and plant age also play a part.

Where this advice applies

All US regions.

Any US garden with lettuce growing when highs of about 85°F or more are forecast for two or more days.

Afternoon shade and heat-tolerant varieties hold longer. In hot-summer areas most lettuce is grown in fall, winter, and early spring.

Exceptions

• Seedlings too small to pick.
• Lettuce you've marked as bolting or finished.

Related guide sections

• Growing lettuce: weather

Reviewed

Sources checked Sept 2026 · awaiting expert review

Gardenplanner research (AI-assisted), pending extension-qualified review

Rule id and version: lettuce.bolt-heat@1