Many urban areas sorely lack green spaces at any scale. Meanwhile, the stubborn vacant lot is a common affliction of the postindustrial city, scourge of property values and community safety. In response, greenthumbs everywhere have been greening cities, from the first squatted gardens of New York’s anti-gentrification Green Guerrillas in the 1970s to the local stewardship of countless anonymous gardeners around the world today. The practice has recently moved beyond the dirt patch to sidewalk cracks, traffic medians, and even streetscape fixtures: Disused newspaper vending boxes have been turned into spontaneous planters, while chainlink fences and telephone poles have been draped with hanging gardens. In all, these efforts are spreading greenery, beauty, and the culture of hands-on urbanism.