I have been buying green onions for years and, until just recently, didn't know this (thank you Pampered Chef party lady)! As long as you don't cut the white part, you can regrow them! Just put them in a jar with some water in the window sill and watch them grow, grow, grow!
Can you believe they grew that much in just 5 days!?!?
The white lines down there are where I cut them to. I probably left about 2 inches of them.
I may never have to buy green onions again! At least, not for a while.