While browsing the gardening pins on Pinterest, I came across one that claimed you could plant the typically unused white root part of a green onion and it would regrow. At the time this sounded ridiculous because I'd never thought about doing anything other than throwing it in the compost bin; now I'm embarrassed I even had that thought.
I raided the fridge to find we had a few green onions left over from a casserole which were nearing the end of their lives. I cut off the wilted parts and planted them in potting soil, though I didn't expect much to happen. They ended up in the window with my spider plants. To my surprise, the green onions started growing and now are thriving. They've grown so tall I can't get them to stand up straight anymore. I can't believe we've been buying green onions when we could have just planted our own. It doesn't get much easier than snipping off what you need and knowing it will grow right back!
There are also other fruits and veggies that can "regrow" like this including pineapples, leeks, carrots, celery, ginger, garlic, sweet potatoes, and bok choy. I searched "regrow" on Pinterest and found all kinds of experiments. I think I'm going to need a bigger windowsill for all the kitchen gardening I want to do.