Several years ago, I had an onion that was starting to grow. The bulb was getting mushy on the outside and fresh, greenish lances were growing vigorously from the top. The bulb wasn't much good to use as a fresh onion and the tops had a flavor that was too mild for cooking, so I planted it.
It was in the spring and the garden was begging (or maybe it was me begging) for something green. I dug a hole and stuck the onion into it, covering up the bulb about two thirds of the way and then I watered it. The weather was still pretty cool, so I thought the green might be short lived, but within three or four days I noticed the color beginning to deepen. Then the lances grew taller and sturdier.
As time moved from early spring to late spring then into early summer, a woodier stem appeared in the center of the lances and grew straight up, strong and tall. I cut a few of them for salad, but let most of them to grow.
Eventually, a bud head formed and almost immediately, it seemed to burst into a bloom of faintest purple/lavendar delicate flowers. The ball of flowers lasted awhile, then began to fade and dry, leaving a cluster of seed pods that was almost as pretty as the flowers.
So far, so good.
I put a paper sack over the seeds and cut the stem, trying to save all the seed I could. I had free onion seed, if you consider that the original onion was ruined.
That's not the only thing you can do with spoiled or leftover bits and pieces of produce that you might throw away. A celery plant on your windowsill? Why not? Look for celery that has a healthy bottom, hopefully with a small, stray root or two, then cut the stalks off (to eat) about an inch from the bottom. Keep the root end in water and it will grow new stalks up from the center.
Those are only two ways to grow food from food garbage, but you can grow interesting plants just to look at, too! Susan Gately explains how in this article: Houseplants from Garbage
And if you don't want to plant them? Dont throw them out. Much of what we call "garbage" is good food.
If growing your own seed intrigues you, make sure you have heirloom vegetables and grow your own every year.
Image is mine, of a celery plant I grew from a root.