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Plant phenology data provide insight into plant community assemblage, ecosystem changes due to global environmental change, and the interrelationship between plants and insect/animal behavior. Knowledge of timing of vegetative and reproductive stages has management implications in controlling non-native range species. We collected species level plant phenology data in the Northern Sapphire Mountains of the Bitterroot Valley, Montana. Species at 26 sites were monitored weekly for plant developmental stage during one growing season. Sites ranged from 1005m to 1822m and included native and exotic range. Analyses address plant phenology in regards to local climate, plant functional groups, plant families, native status, microsite conditions, and plant structure. For 70 species, we show plant stage from emergence to senescence, including date of emergence, budding, flowering, fruiting, mature fruit presence, and senescence. We compare native plant phenology to that of non-natives. The dominant exotic forbs emerge early, and flower and set seed later in the season than most natives. This suggests that to minimize damage to native species, herbicide treatment should occur late in the season when most native plants have senesced. These data will be used to plan seed collection efforts and herbicide application. Subsequent years of this long-term monitoring project will illuminate changes in plant patterns due to changing climatic conditions.