The only canning recipe I could find for scallions or green onions was Pickled Scallions on several websites. So I went with that. After they were washed, I cut them to fit the 1/2 pint jars and stacked them in layers in a bowl with salt, covered them with water and allowed them to sit overnight.
Click here to see more on this recipe: https://duckandjunebug.wordpress.com/2010/03/13/pickled-scallions-blah/
