My lovely ten-year old son, Zayne, (and I) had a lot of fun working on his 4th grade science project this spring. His subject was "Regrowing Green Onions." (No volcano-creating or solar system dioramas this year!!!)
I was anxious and excited to work on this with him because I use a lot of green onions in my cooking ... and if they can be regrown and regrown and regrown without having to keep purchasing more and more (and spending more and more), then that is a good thing! We tried growing in both water and soil. Soil worked best, although the ones in water grew just a tad faster. The ones in soil were sturdier and didn't bend and fall over (no offense, water ones!). You can find the instructions of how we did it within the "Procedures" portion of his board. Your kids will think it's cool to see something grow so fast indoors and from just a root ... and, you'll think it's cool that it's saving money and living frugally!
Here's some photos of the growth process.