Romaine vs Iceberg: Head Shape Plus Heat Tolerance
Romaine vs iceberg comes down to head shape, heat tolerance and timing. University of Illinois Extension says romaine forms an upright, elongated head. Iceberg is a crisphead type that is extremely sensitive to heat. NC State Extension says romaine does better in heat than head lettuce.
The short answer
Romaine is upright and handles heat better. UF IFAS Gardening Solutions says romaine has the most upright growth of the main lettuce types and a crunchy midrib. Iceberg is pale green with leaves layered tightly in a ball. Illinois Extension says crisphead must mature before the first hot spell of summer.
How do the heads differ?
University of Illinois Extension lists five lettuce types, including cos or romaine and crisphead. Romaine forms an upright, elongated head.
University of Minnesota Extension describes romaine as tall, compact heads. It calls crisphead or iceberg a dense, solid head.
UF IFAS Gardening Solutions says iceberg is pale green with compacted leaves layered tightly in a ball. Romaine is known for its distinct, crunchy midrib.
Which handles warm weather better?
NC State Extension says leaf and butterhead types tolerate heat better than romaine. Romaine itself fares better in heat than head lettuce.
Illinois Extension says crisphead types are extremely sensitive to heat. If an early heat wave strikes before they mature, they almost certainly fail.
NC State says high temperatures of 70 to 80 degrees F plus dry soil can trigger bolting. Bolting turns leaves bitter and halts leaf production.
| Trait | Romaine | Iceberg |
|---|---|---|
| Head | Upright plus elongated | Tight round ball |
| Heat | Better than head lettuce | Extremely sensitive |
| Spacing | 6 to 8 inches | At least 10 inches |
| Picking | Outer leaves or cut head | Whole head once |
Source: UF IFAS Gardening Solutions plus NC State Extension.
How long does each take?
NC State Extension says head lettuce is ready 70 to 80 days after seeding or 60 to 70 days after transplanting.
Leaf lettuce is ready 50 to 60 days after seeding, the same source says. Illinois Extension notes head lettuce must be transplanted in most locations.
Illinois says crisphead started in late summer to mature in cool fall weather has a much better chance of success. Finish spring planting at least a month before hot days arrive.
How to: step by step
- Choose romaine for warmer spells.
- Choose iceberg for a long cool season.
- Transplant iceberg in most locations.
- Space iceberg at least 10 inches apart.
- Space romaine 6 to 8 inches apart.
- Time iceberg to mature before summer heat.
Troubleshooting
Iceberg failing to head: early heat. Plant for fall.
Bitter leaves: bolting. Pick sooner.
Early bolting: dry soil. Water evenly.
For related reading see cannabis leaf anatomy, cannabis heat stress plus companion plants when growing marijuana. Kind Seed Co also stocks cannabis seeds.
Sources
- Lettuce, home vegetable gardening, University of Illinois Extension
- Growing lettuce, endive plus radicchio, University of Minnesota Extension
- Lettuce, UF IFAS Gardening Solutions
- Lactuca sativa (lettuce), NC State Extension Gardener Plant Toolbox
FAQ
Is romaine easier to grow than iceberg?
Generally yes. University of Illinois Extension says crisphead or iceberg types require the most care and must mature before the first hot spell. University of Minnesota Extension says loose leaf varieties are easiest. NC State says romaine handles heat better than head lettuce, though less well than leaf types.
Can lettuce grow in partial shade?
University of Illinois Extension says heat tolerant varieties, mainly loose leaf types, may be grown in the shade of taller crops through most of summer. That works if extra care is taken with irrigation and soil. Seedlings started in shade can later move to moderate sites.
Can leaves be picked from romaine?
Yes. UF IFAS Gardening Solutions says to cut larger outer leaves of romaine first and let inner leaves develop, which prolongs the harvest. You can also cut the whole head two thirds of the way down and regrow it. Iceberg can only be harvested once as a whole head.
How far apart should each be planted?
UF IFAS Gardening Solutions says to space transplants 6 to 8 inches apart, except crisphead, which needs at least 10 inches. NC State Extension agrees that head lettuce generally needs 10 inches between plants. Minnesota Extension suggests rows at least 18 inches apart for lettuce.
Can lettuce grow in containers?
NC State Extension says lettuce can be grown in containers that hold a minimum of 2 quarts and are 6 to 8 inches deep. Lettuce grows rapidly to 6 to 12 inches tall and wide. Plant seeds a quarter inch to three eighths of an inch deep.
