Guerrilla gardening is the practice of reclaiming abandoned land (which the gardeners do not own) and "bombing" it with plants, fruits and vegetables. Some do it under the cover of night, while others prefer doing it in broad daylight. There are different motives for why people do it, whether it be to beautify a neglected area, provide food, be part of the urban agriculture revolution, or to feel a sense of community with those around them.
While the practice has been around since the 1970s, London-based Richard Reynolds is currently the most well-known guerrilla gardener out there, and he's done a lot to expand the worldwide community of guerrilla gardeners. He has a helpful blog, guerrillagardening.org, has written the gospel on guerrilla gardening, and takes the time to spread the message everywhere he goes, from London to Botswana.
Technically, and ridiculously, guerrilla gardening is illegal, but it doesn't look like there have been many garden-related arrests, so we're going to assume it's a low priority for cops. We've compiled some tips from the master guerrilla gardener himself, along with videos of guerrilla gardeners in action. Take a look, and start your own rogue gardening group!