There are three different ways you can store scallions
Plastic bag or ziplock
Heavy bottom jar
Store on a Windowsill
Place the scallions root side down in a tall heavy-bottomed jar that holds them without them flopping over. Fill the jar with an inch or two water, just enough to cover the roots. Place the jar on the windowsill in your kitchen. Your onions will not only stay fresh but will also continue to grow. Change the water every couple of days.
Store in the Refrigerator
Place the scallions root side down in a tall heavy-bottomed jar that holds them without them flopping over. Fill the jar with an inch or two water, just enough to cover the roots. Place the jar in the refrigerator with a plastic bag covering the tops of the scallions. Be sure to cinch the bag a bit, either with a rubber band or if using a ziplock close each side a bit. This helps keep some humidity within the bag. Store in a safe spot in the refrigerator so it does not get knocked over. Change the water every couple days.
Store in a Damp Paper Towel
Wrap the scallions in a slightly damp paper towel. The dampness provides the humidity needed for proper storage; if the towel is too wet though, it can promote rotting. Place the wrapped scallions inside a plastic bag or storage container; it doesn’t need to be sealed airtight. Moisten the paper towel again if it dries out or replace it if it becomes too wet.