We collected plant phenology data in the Sapphire Mountains, Montana, USA, by monitoring developmental stages of 101 native species and 21 exotic species during weekly visits to the sites from March to November 2013. We compared the start, end, and length of the emergence, flowering, and seed maturation phases for exotic and native plants. Short-lived forbs, perennial forbs, and perennial grasses were analyzed separately. Exotic plants emerged earlier, began and ended flowering later, and had later ends to emergence and dispersal phases across all functional group comparisons. The emergence phase for exotic perennial forbs averaged 13.8 weeks longer than for native perennial forbs, the flowering phase was 3.4 weeks longer, and the seed dispersal phase was 8.3 weeks longer. The window for emergence and flowering for forbs, shrubs, and grasses (March to November) did not differ between natives and exotics. The results generally support the conclusion that the exotics have an advantage over the natives in priority of growth and wider niche breadth, rather than occupying vacant niches. Seed set time varied in duration from 1 to 23 weeks from April to November. Our results provide insights into invasion mechanisms and selection of native plant materials to compete with invasive species. We discuss implications for seed collection and herbicide timing.