Grow Onions in containers and use the cut and come again method. choose a container to plant them in. Since onions have a shallow root system it only needs to be inches deep minimum. Onions require a high source of nitrogen
"The next time you have green onions, don't throw away the white ends. Simply submerge them in a glass of water and place them in a sunny window. I periodically empty out the water, rinse the roots off and give them fresh water." Neat, I just bought some.