Its true! Don't toss out those white stringy parts of your green onions. Leave about an inch and a half of the ends bundle them up with a rubber band and set them in a clear glass filled with water. Make sure it is in a sunny spot (mine isn't in a super sunny spot) and watch the magic happen over the next few days.
Keep the water clean and you'll have green onions on hand for a couple months!
A neat trick I learned from my dad who was a huge onion fan.