Published July 1, 2010. From Cook's Illustrated.
Too often we find that scallions go limp after just a few days in the fridge.
To prolong their shelf life, we tried several different storage methods, from wrapping them in moistened paper towels placed inside an open zipper-lock bag to tossing them naked into the crisper drawer. We found that standing the scallions in an inch of water in a tall container covered loosely with a zipper-lock bag worked best. Stored this way (with the water refreshed every three days), our scallions lasted for well over a week with very little loss in quality. (We’ve also used this trick to rejuvenate limp celery and broccoli. Standing their root ends in water can restore moisture and firm texture.)
ROOTED IN FRESHNESS
With their root ends stored in a little water, scallions will stay firm and fresh for well over a week.