I've been harvesting my romaine by the leaf on a weekly basis. (I'd love to be able to just pick as I need it, but that's not practical...)
I wash it as soon as I get it home, lay it out in a single layer on cotton terry dish towels and roll up the towels and put them in a plastic bag in the fridge. This worked well the first few times I did it, but this week and last week the leaves have been limp within a day or two. They are still edible, but not crisp, more like pressed flowers that haven't dried all the way.
Is there a better way? Should I be sealing the leaves in the plastic bag? (I leave it open-ended b/c the towels are bigger than the bags.) Should I wait to wash them and then only wash what I'm going to use? Any other ideas?