How To :
- Use spring onions as you normally would.
- Save bulb leaving about a 2 inch stem.
- Put them in a small jar, covering roots with water. That’s it!
- Put the onions where they will get some natural light. They will keep growing back! Use kitchen sheers to snip what you need.
-Change the water every 3 days or so.
Source : How to Grow Spring Onions in a Jar