This article provides a sociological explanation for urban “greening,” the normative practice of using everyday signifiers of nature to fix problems with urbanism. Although greening is commonly understood as a reaction against the pathologies of the industrial metropolis, such explanations cannot account for greening’s recurrence across varied social and historical contexts. Through a study of greening in Germany’s Ruhr region, a polycentric urban region that has repeatedly greened in the absence of a traditional city, I argue that greening is made possible by a social imaginary of nature as an indirect or moral good, which I call urbanized nature, that is an outcome of, and subsequently becomes a variable in, urbanization. I draw on processual accounts of urbanization and the sociology of morality to explain urbanized nature’s emergence in the Ruhr at the beginning of the twentieth century, and its use to fulfill two competing visions of urban democracy in the postwar period. I find that rather than an ideological reaction against cities, greening is an aspirational practice that can be mobilized by a range of actors in a variety of places and times. By showing how a new social imaginary made new forms of moral action possible and how those ideals were then materialized in urban space, this article draws attention to the role of cultural imaginaries in urban change and to the material consequences of moral beliefs.