Yesterday I planted one of our beds out in green onions. Not seeds or sets mind you but with scraps of root ends that get chopped off in prepping and normally thrown away or put in to compost. I save all of our green onion roots and every month or so plant out a nice little bed of them. It keeps us in fresh green onions all year as well as the greens to dehydrate consistently and by doing this it makes us sustainable in that aspect of our life.
Replanting the root ends is not something that one can only do when they grow their own nor are green onions the only veggie that you can do this with, but more on some of the others in a different post. In fact, store bought varieties do wonderful regrowing and it is great to know that you have a food on hand that is essentially ever growing or recycled. After just one cycle of regrowth your onions will have paid for themselves and from there on out it is money saved. Another neat thing about these greenies is that you don't even have to have a pot with soil to do this with, you can simply use a bowl of water. Talk about a super, simple, lesson on basic hydroponics and science for the kiddies.
Any who, all I do is cut the bottom 3/4 of an inch or so of the green onion when using leaving a tiny portion of the onion itself and the root. I then throw them in a cup of water in the fridge and let them sit until the next time I plant. If it is going to be a while before the next planting, I change the water every couple days until I do. They will stay good this way for a few weeks if not longer.
When I am ready to plant I just stick the root end down in the soil and cover with an inch of soil. They will regrow rather quickly and be ready to harvest again in a couple months. Once they are a few inches tall begin to trim the greens and use them in soups, salads or whatever else you enjoy them in. I like to dehydrate mine for veggie dips and salad dressings.
To grow the onions in water simply fill a shallow open container with water. Completely cover the onion root with water. Place the container in a sunny location to grow, the plants don't need direct sunlight so any room that is fairly well lit will work, although, the more sun they receive the faster they will grow. Replace water every few days as it evaporates. As the onions grow, stand them upright by leaning them against the side of the container so that the top part of the onion is not submerged in water. Once grow either, eat and repeat or plant in to soil.