Several of my local grocery stores had scallions on sale this week, $0.99 for 3 bunches (or $0.33 a bunch). I bought one bunch at a local Korean market and promptly cut them in half: one half was all green, and the other half was both white and green. I chopped up the all-green half and put it in Tupperware for later use. Then I put the white parts (with the roots intact) in a mason jar with a bit of water and stuck the jar near the window. Why? Because scallions will keep growing in water!
As a single person cooking for one, it’s pretty hard for me to finish a whole bunch of scallions. I usually just need one or two sprigs, but they’re always sold in bunches. They seem to wilt in the refrigerator very quickly, too. I used to think it was a waste to even buy scallions until I discovered this water-growing trick on the internet.
You may be able to do this even if you don’t have a sunny window for your jar of scallions. It has worked for me it in the middle of winter in southern Norway, where there is just a few hours of sunlight a day.