Last year, as an experiment, I decided when cutting onions, to leave 1/4″ of the lower bulb intact and all roots as they are. I then simply put them on the soil of my herb trough (roots down of course) to see what would happen to them.
They actually sprouted fresh roots into the soil! I put them back covering the roots with soil and they grew, but because of being uprooted, grew very slowly.
With the next few onions used, I decided to try leaving roots plus 2 layers of the bulb intact & replanted. They regrew and are now providing me with “spring onions” or onion-tops which I use in omelets, stir-frying, garnishing, etc.
I guess I have found a 2nd way of getting spring onions for the kitchen. I don’t buy them anymore. When needed, I select the thickest ones and just cut individual “leaves” 1-inch from the base, new “leaves” will appear from the old cut-up bulb again. So far I’ve learned they can continue growing in winter so I’m observing very carefully.
A neighbor gave a an onion she found in her refrigerator that had already sprouted so in it went into the onion patch. That too has sprouted. I have always grown onions from seeds but this has got me wondering if I can cultivate them from splitting the initial root piece into 2 & then replanting. More experimenting needed.