How to preserve scallions?
Scallions are very touchy. You don't want them to dry out, and yet you don't want them too wet or they will get slimy and disgusting.

What works best for me is remove any binding holding them together (e.g. rubber band or twisty-tie), (and certainly trim off any parts of the scallions that are already damaged and/or slimy), don't wash until you are ready to use them, wrap the bunch of scallions loosely (but completely covered) in a paper towel, and then store that wrapped bundle in a flimsy plastic bag (maybe the one you brought them home from the supermarket in) in your refrigerator. 

Sounds "fussy" when you lay out all the steps like that, but really, it's not a whole lot of work. Removing the rubber band etc. prevents damage where it would cut into the veg. flesh, paper towel absorbs condensation &amp; liquid water which will rot the scallions (paper towel will prob. become slightly damp after a while in the fridge, but this is OK), plastic bag prevents evaporation of moist air.

I find this works well for lots of greens, esp. cilantro - the worst offender in the demanding vegetables category.

P.S. If you aren't too squeamish, you can even remove the very outermost layer of a scallion which has begun to "slime-out", wash the remainder right before using - &amp; it's fine!