It actually works!
I took these from the sill back to the garden and they took off.
1 Cut the Onions
Remove the green onion stalks down to about an inch, leaving the bulb and roots intact.
2 Plant the Bulbs
Place the bulbs in a small amount of water covering the white part of the bulb or Plant the bulbs root side down either in a container that has drainage holes or directly in your garden soil. Make sure the planting area gets at least six hours of sunlight per day. Cover the bulbs completely with rich, well-draining soil, but leave the short stalks sticking out above the soil.
3 Water Regularly
Water your onions whenever the container or soil starts to dry out, but don’t let the bulbs sit in soggy soil. You should see noticeable regrowth in the stalks within days.
4 Cut Stalks as Needed
To harvest, simply cut off as much of the stalks as you need.