Wow, just stumbled upon this little gem of a website called Guerilla Gardening. It's a community organization (founded in England) which draws attention to wasted urban space, or in the words of a Guerilla Gardener: it performs "sneak attacks on horticultural wastelands". This amazing group of people lash out by secretly tucking veges into city flower beds, making better use of space and resources in crowded urban areas.
Just amazing... it's almost poetic. Apparently, it's also really fun! People dress up as ninjas, ‘arm’ themselces with "seed bombs" to deploy on rooftops and concrete spaces, and sneak out in the pitch dark to plant blueberry bushes or sweet peas.
They also have instructions on their website to plan your own Guerilla Gardening attack! So dust off your balaclava and get planting!