I found the instructions of how to plant onions from discarded bottoms. Unfortunately it didn't work for me. I will try again. Has anybody had luck with it?
You will need: onion, clean knife, cutting board, starter pot with potting soil (optional)
Slice Off Onion Bottom
Chop off the onion bottom with all the roots still intact. The more of a bottom you leave on, the better. Try for 1.5-2 inches of attached "meat". Allow to dry for a few hours to a couple days in a shaded, well-ventilated area to allow for callousing. Note: You might only need a few hours for callousing. If the cut portions are dry to the touch and slightly shriveled
Fill the starter pot 2/3 of the way full and compact. Create an indentation in the center to cradle the onion bottom and allow for good soil contact. Cover with 1-2 inches of soil. Water as needed. Note: You can skip the starter pot if you can't be bothered and plant it directly in the ground.
Once the onion bottom has developed a few leaves, remove from the pot. Remove old onion scales. Separate plants as needed by slicing between plants and leaving a portion of the roots attached. You may have more than 1 plant develop from a single onion bottom. Replant in a prepared growing bed. Cut leaves down to 1/3 of the size to allow the bulb to develop. good luck.