Phenologists track the seasonal behavior of plants and animals in response to climatic change. During the second half of the twentieth century, phenologists developed a large-scale project to monitor the flowering time of the common lilac across the United States. By the 1960s, this approach offered a potential plant-based indicator of anthropogenic climate change, a biological signal amidst the emerging narrative of increasing levels of atmospheric carbon dioxide. As a tangible representation of changes in climate—warmer temperatures lead to earlier blooming—phenology (...) proved highly legible to scientists, politicians, and laypeople. Yet, as phenology gained broader repute in the 1960s, both in agricultural stations and as a component program of the International Biological Program, it struggled to align itself epistemically with the regnant disciplinary assumptions of mid-century ecology. Operating in the hinterlands between laboratory and field, biology and meteorology, ecological theory and agronomy practice, phenologists challenged prevailing notions of the model organism and what it meant to study biology in the field. Rebranding the discipline as a component of ecosystem modeling, scientists successfully brought phenology within the purview of mainstream ecology. In so doing, however, they obscured its climate-relevant meteorological character and stymied the development of a biological narrative of climate change. (shrink)