Information about regrowing vegetables that you have purchased from the grocery store has been floating around the old information superhighway (aka, the internet) recently. Regrowing vegetables refers to basically inserting the cut root ends of produce into plain old water and waiting for them to grow. Buzzfeed lists scallions, garlic sprouts, romaine lettuce, carrot tops and basil as vegetables that are easy to regrow. Theoretically you can use any veggie that has a root end intact, as well as some others (like growing a pineapple from the top).
When I first heard of regrowing vegetables, I was pretty skeptical. I mean, vegetables are living things and need nutrients to grow, just like anything else. These nutrients can't be provided from water alone, so how is that growing supposed to happen. But if it worked, wouldn't it be awesome? Just think how many fewer groceries you'd have to buy! I decided to give it a try.
The first veggie I tried was some Chinese cabbage from my CSA. I cut off the usable leafy part for my stir-fry and stuck the bottom (root) into a container of water instead of throwing it away. I put it on my kitchen windowsill where I knew it would get a lot of sunlight. I was pretty excited when it was visibly growing after only a couple of days (above picture).
At this point, I added bok choy, scallions and red lettuce to my experiment. They too, started growing right away. BUT - this is pretty much where the excitement ended. After a week, both the lettuce and the cabbage pretty much stopped growing. I was left with maybe enough of each to feed my cockatiel once. The bok choy and scallions did keep growing for maybe another week, but they too went downhill.
At the 3 week point, I took one last set of pictures. You can tell that the bok choy and the scallions (the two left) significantly taller than before. The lettuce and cabbage (the two right) are pretty much the same size as the one week picture, but looking a little worse for wear. Even with regular water changes, all the plants had started getting pretty slimy looking and brown where they were sitting in the water. The lettuce had begun to wilt. They even smelled pretty rank. Basically, they were rotting - Eew. Not something I would ever want to eat.
Best worst of all, when I looked closely at the bok choy, it was absolutely covered with tiny little bugs - like aphids or something. I do realize that all of my produce has had bugs on it at one time or another, and that's fine. I just don't want them in my kitchen.
Of the four veggies I tried, the only one I could see realistically being regrown in your house and actually getting any use of it is scallions. They grew significantly more than the others, and didn't get as rotten on the bottoms as the rest. Since you often don't use many scallions at once, you may get some use out of them, especially if you had a few growing at different stages at the same time. However, you're not going to be able to regrow them forever. Due to the rotting factor, I think you'd be able to regrow a scallion once, and that would be it. And scallions don't really cost that much - I'm not sure getting an extra few inches of scallions out of the ones you buy is worth it, considering the fact that you'd have scallions sitting on your windowsills at all times.