This is the kind of information that once you know it makes sense. When you are harvesting loose leaf varieties of lettuce, leave the roots in the ground. Cut your leaf lettuce off about 1/2 inch above the ground as to leave the stump and attached roots in the ground.
In about 5-7 days you will see new leaves sprouting up and in about another week you will have more leaves to harvest. If your weather stays cool enough... you can often get another harvest or two from one loose leaf lettuce plant.
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