Resources play an important role in shaping the evolution of plant defensive strategies. Much research has focused on how resource availability impacts the overall concentration of specific defensive compounds, particularly among-species. Yet, how resource availability influences overall phytochemical diversity within species, and how this in-turn might affect herbivore damage is less well understood. Using Monarda fistulosa, a species that produces diverse terpene compounds and distinct chemotypes (i.e., thymol or carvacrol), we addressed three primary questions: 1) How do phytochemical components (i.e., total concentration, Shannon diversity, and chemotypes) vary between distinct populations from two large, widely separated regions that differ in climate and productivity? 2) How do these components influence attack by different herbivore species? 3) What are the growth costs of higher phytochemical levels in different chemotypes? Seeds were collected from 12 populations, six from a low-productivity/resource environment in Montana, and six from a high-productivity/resource environment in Wisconsin. Seedlings produced from these seeds were transplanted to a common garden in Wisconsin. Over two growing seasons, we analyzed terpene concentrations, quantified the number of herbivores damage, and measured plant above-ground biomass. Plants from Montana exhibited higher terpene concentrations but lower diversity, whereas those from Wisconsin displayed lower terpene concentrations but higher diversity. Total terpene concentration emerged as the primary predictor of herbivore damage, although some differences were observed between region of origin and with terpene richness. Herbivores exhibited mixed responses to phytochemistry; some herbivores were negatively affected, while one species, a specialized leaf galler, responded positively. Costs of producing defenses were evident, manifest by negative correlations between plant biomass and total terpene concentration (but not chemical richness or Shannon diversity). Our study revealed that regional differences in resource availability and productivity can influence the evolution of phytochemical concentration and diversity, which, in turn, affects plant damage and incurs growth-related costs.