Scallions, also known as green onions, are relatively finicky vegetables. If you don't store them correctly, your scallions will wilt and turn into a dark green, moist mass that you have to toss. So how do you store scallions to keep them as fresh as possible for as long as possible? Well, unlike regular onions, which stay freshest at room temperature, scallions should be stored in the fridge. That's because scallions are more like leafy greens than they are root vegetables, and so you should be treating them more like herbs or spinach than potatoes or regular white or yellow onions.
The best way to keep scallions fresh, according to the editors at Cook's Illustrated, is to stand the scallions upright "in an inch of water in a tall container covered loosely with a zipper-lock bag." They then popped the whole contraption into the fridge, and when stored this way, with a water change once every three days, "our scallions lasted for well over a week with very little loss in quality," they note. Two hints: Remove the rubber band that are likely keeping the stalks together, and don't wrap a rubber band around the plastic bag. That'll trap in moisture and cause your scallions to wilt more quickly.
Alternatively, you can store green onions in a "breathable" bag in the high humidity drawer of your fridge, writes Dana Gunders in Waste-Free Kitchen Handbook: A Guide to Eating Well and Saving Money By Wasting Less Food. Think a mesh or open paper bag, not a closed plastic bag.
If your scallions do start to wilt and lose that crisp texture, you can shock them back to life. "Soak root ends in cold water for an hour to revive," explains Gunders. (Pro tip? Putting wilted produce in cold water is an easy way to bring a lot of different vegetables and herbs back to life.)
And that's all there is to keeping scallions fresh and crispy for as long as possible.