Awhile back, I read about a woman who takes random produce - garlic, potatoes, onions - and puts them back in the ground to see what will happen. Sometimes she's rewarded with fresh growth, sometimes she digs up a rotten tuber. I admire that entrepreneurial spirit of homesteaders who aren't afraid of a little failure now and then. It's a wonderful attitude to adopt. The last bunch of scallions that I bought were the first victims of my own experimentation.
After cutting off the tops for dinner one night, I plunked the rest in a cup of water, using skewers to keep the bulbs from completely submerging and potentially getting the ick. The photo above was taken less than 24 hours after I plunked them in their new hydroponic haven. As you can see, after that short amount of time, there was already new growth creeping up from the cut line.
A few weeks later and they've completed regenerated. They just require a change of water every couple of days. I have no idea how long they'll last this way but considering I've learned how to cut the cost of a bunch of scallions at least in half, I'd call this test a success.