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How to harvest romaine lettuce
Harvest the romaine heads about 65-70 days after planting the seeds.
When grown from seeds, romaine lettuce takes only a little less than 3 months to fully mature. You can tell when the heads are mature by their visual appearance: they'll have a dark green color and look leafy and open.
Unlike iceberg lettuce, the romaine heads will not be densely closed in upon themselves when mature. Cut the entire head off above the base if you want a second harvest.