Guerilla Gardening.
Dig it!

Tools of the guerilla gardener:
-trowel
-seeds or transplants
-bucket of compost
-vermiculite
-water

There are two components to guerilla gardening: utilizing space to grow food, herbs, etc; and reclaiming space as an act of rewilding the Earth.

Its simple: find some unused piece of land and garden it!  Try not to garden too close to roads (toxins) or where maintenance might be working (lawn mowers).  Get your community to reclaim some public space and plant a community garden in a park, vacant lot, etc.  To help rewild the city, plant flowers, herbs, vine crops, and other seeds in side walk cracks, along building sides, lawns, rooftops, golf courses, etc.  Be creative. 

Primal Seeds

Phantom Treeplanter's Manifesto

From Cities to Gardens