There was an exchange on one of the gardening forums about growing scallions from the cut-off roots of the ones we buy at the supermarket. After seeing how long it would take to grow them from seed, I set about trying it immediately!
Yummy! I love a few scallion rings floating in soup, but dislike buying a bag at the market and cleaning them up only to have them go to waste, as they so often get forgotten in the fridge. Having them fresh and organic is fun, they are a pretty houseplant, and seen them on the window sill reminds me to snip a few and eat them.
One note of warning on these, though, they want their water changed frequently, or they do get stinky feet. Here is a post on my gardening blog about growing scallions, for those who haven't seen it:

Your original writeup was great. Once they start regrowing, they take off quickly. Thanks for the great ideas.
Posted by: Red Icculus | March 16, 2009 at 04:57 PM