If you don't have room for a vegetable garden you may want to consider creating an Edible Landscape. Use fruits and vegetables as your feature plants and your garden landscape will be both beautiful and practical.
This article titled "How To Grow Sprouted Onions" at Alternative Gardening talks about exactly that. I had no idea. All this time, if I didn't eat an onion in time, I would simply plant the whole thing as-is in the soil.