When to Plant Lettuce
Planting Window
- Sow or transplant
- ~2 weeks before last frost
| USDA Zone | Typical Window |
|---|---|
| Zone 5 and colder | April, with several successive plantings |
| Zone 6-7 | March, pause through peak summer, resume August |
| Zone 8 and south | Fall through spring only |
Lettuce has a genuinely unusual quirk among garden seed: germination itself slows and can fail above roughly 80°F soil temperature, an actual heat-induced dormancy response rather than just general heat stress - which flips the normal seed-starting logic most gardeners are used to, where warmer soil almost always means faster germination.
Direct Sowing or Transplanting, Early
Cool spring soil is actually closer to lettuce's ideal germination temperature than the warm soil most other vegetables are waiting for at the same point in the season, which is part of why an early planting so often outperforms one held back to match a more typical spring schedule.
Heat-Tolerant Varieties for a Longer Summer Window
Some lettuce cultivars, particularly certain looseleaf and batavia types, are bred specifically for better heat tolerance and slower bolting than standard varieties - useful for gardeners trying to stretch a summer lettuce supply, though even heat-tolerant types eventually succumb to sustained high heat the standard varieties can't handle at all.
Sowing Indoors on Hot Days to Beat the Germination Problem
When outdoor soil is too warm for reliable germination but a gardener still wants to keep a summer succession going, starting seed indoors in a cooler spot (or even briefly in a refrigerator to trigger germination before sowing) and transplanting seedlings out is a workaround some gardeners use specifically to get around lettuce's heat-germination-dormancy quirk.
Shade Cloth Extends the Cool-Season Window
A simple shade cloth over a lettuce bed during the hottest weeks of the transition into summer can meaningfully lower soil and air temperature around the plants, buying extra time before bolting sets in - a cheap, practical extension of the growing window that doesn't require choosing a specific heat-tolerant variety.
Head Lettuce Needs More Lead Time Than Looseleaf
Looseleaf lettuce can be harvested informally over weeks by picking outer leaves, while head types (romaine, iceberg, butterhead) need to reach full maturity before a single harvest, which generally means starting head lettuce a bit earlier and being more precise about timing it to mature before heat arrives than the more forgiving looseleaf types require.
Zone boundaries follow the USDA Plant Hardiness Zone Map (2023 revision); frost windows reflect NOAA/NCEI climate normals. Both are typical historical ranges, reviewed annually - not a forecast or a guarantee for any single year. See Methodology & Sources.
Frequently Asked Questions
Why didn't my lettuce seed germinate when I sowed it in early summer?
Warm soil is the most likely cause - lettuce seed genuinely goes into a heat-induced dormancy above roughly 80°F, an unusual trait most vegetable seed doesn't share, so seed that would germinate fine in cool spring soil can simply fail to sprout in hot midsummer soil regardless of watering or seed quality.
Does head lettuce need to be started indoors as transplants, or can I direct-sow it like looseleaf and still beat the summer heat?
Many gardeners do start head lettuce indoors specifically to get that extra lead time, sidestepping lettuce's heat-germination quirk entirely by germinating seed indoors under cool, controlled conditions instead of waiting on outdoor soil to cooperate. Looseleaf types, needing much less lead time to begin with, are more commonly just direct-sown, though either method works for either type if timing allows.
My lettuce has already started to bolt and taste bitter - is it worth doing anything with it besides pulling it out?
The leaves won't lose that bitterness, so it's not going to be worth eating from at that point, but a fully bolted plant is a reasonable source of homegrown seed if you let it finish flowering. Lettuce is self-pollinating and doesn't cross easily with other lettuce nearby, which makes it one of the more forgiving vegetables for a beginner to try seed-saving on before composting the spent plant.