Now this is a good idea! 

Guerrilla gardening is the art of using a piece of land which you do not own to grow something. One step removed from actual guerrilla warfare, guerrilla gardening takes land not for the people, but for nature; returning misused or disused land and finding a purpose for it. Guerrilla gardeners come late in the night with watering cans, compost and gardening gloves, and turn rotting sods of grass outside some condemned building into a vegetable patch, a clump of daffodils, or a flowering rosebush.
[kuro5hin.org]