The utilitarian Wardian case, a precursor of the modern-day terrarium, was used for packing and transporting plants around the globe, and has long been recognized as an instrument of nineteenth-century colonial enterprise and exploitation. However, the decorative versions of this device installed in Victorian homes performed a different sort of ideological work. In this essay, I investigate the graphic descriptions of coal smoke and air pollution that appeared in nearly every account of terrarium technology from this period. Combining scholarship on the environment with theories of the miniature, I argue that the Wardian case helped the Victorians conceptualize their increasingly fraught relationship to the natural world. Analyzing the repeated emphasis on air quality in textual and visual representations of the Wardian case recovers the story of a manufactured commodity that inadvertently brought the consequences of industrialization to the forefront of Victorian domestic life.