Romaine Lettuce
Lactuca sativa var. longifolia
The most heat-tolerant lettuce and the one that survives a zone 6b/7 summer longest.

The one to grow in warm weather
Romaine holds against heat better than butterhead or crisphead, staying sweet for weeks after the others have turned bitter. If you want lettuce into June, this is the type. Even so, afternoon shade in a heatwave buys another two weeks.
Upright habit changes the spacing
Romaine grows vertically into a tall loose head rather than spreading, so it takes less horizontal room than a crisphead - ten to twelve inches is enough. That upright growth also keeps the leaves off the soil, which reduces bottom rot and slug damage compared with a butterhead.
Sow shallow, in the cool
Lettuce seed needs light to germinate, so barely cover it. Above about 80F it goes thermo-dormant and simply will not come up - for a late-summer sowing, start indoors somewhere cool or pre-chill the seed in the fridge for a few days.
Water and feed steadily
Shallow-rooted and mostly water. An inch or more a week and light regular nitrogen keeps growth fast, and fast growth is what makes romaine tender and sweet. A check in growth gives tough, bitter leaves.
Blanching the heart
Romaine hearts self-blanch to some extent as outer leaves shade them. Loosely tying the outer leaves together about a week before harvest gives a paler, sweeter, crisper heart - the classic treatment for a proper Caesar.
Tipburn
Brown crisped margins on inner leaves come from uneven water and rapid growth in heat, not from disease. Even moisture and a mulch prevent it.
Pests and disease
Slugs, aphids in the heart where they are hard to rinse out, and rabbits. Downy mildew shows as yellow patches with grey fuzz underneath in cool damp weather; space for airflow and pick resistant varieties.
Harvest and storage
Cut the whole head at the base in the early morning, or take outer leaves individually for a longer picking. Plunge into cold water, spin dry, and it will keep one to two weeks in the fridge - the best keeper of the lettuce types thanks to its thick ribs.
- Days to harvest
- 55-75
- Spacing
- 10-12 in
- Row spacing
- 18 in
- Sun
- Full, part shade in heat
- pH
- 6.0-7.0
- Bolts above
- ~85F
- Habit
- Upright head
- Storage
- 1-2 weeks