Answer: Head lettuce such as butter and iceberg should be harvested when the heads are full size. If your butter lettuce is developing a large stem and growing straight up, it's about to bolt (set seeds) and will not be tender and tasty. Harvest when the leaves look mature and the head is about 7" across. I usually measure my lettuce by holding my hand over the head and stretching out my fingers. If the head is as large as my outstretched hand, it's big enough to harvest. Romaine lettuce can be harvested all at once or you can pull individual outer leaves off each plant. Since romaine expands from the center out, as long as you leave the crown of the plant intact, it will continue to develop new leaves. If the stem of the plant begins to elongate, it's ready to bolt and should be pulled from the ground. The younger the lettuce leaves, the more tender and tasty, so don't let the plants get too big or too old. Hope the above helps you determine when to harvest your lettuce!
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