Have you ever heard about Guerilla Gardening?

Most people have not.
Guerrilla Gardening means that you grow your own vegetables and fruits wherever you possibly can, even the smallest spaces. According to some proponents of this kind of gardening, 30 square meters (app. 36 square yards) are enough to grow all the food one person can eat for a whole year.

Therefore Guerrilla Gardening has become very popular in many inner-cities. For example, I just discovered that app. 25% of the vegetables consumed in Singapore come from this kind of gardening.

You can read more here, if you like:
http://www.garden-anette.com/guerilla-gardening/