Shifts in the timing of life history events, or phenology, have been recorded across many taxa and biomes in response to global change. These phenological changes are likely to have cascading effects on biotic interactions and community structure, but untangling the realized demographic consequences of these shifts is challenging. Focusing on an annual grassland plant community, we examined how experimental changes in precipitation affect flowering phenology in a community context and explore the implications of these shifts for competitive interactions and species coexistence. We found that changes in rainfall shift some species flowering phenology, but sensitivity differed among neighboring species. Four of seven species we studied started and/or peaked flowering earlier in response to reduced water availability. The idiosyncratic shifts in flowering phenology we observed have the potential to alter existing temporal dynamics that may be maintaining coexistence, such as temporal separation of resource use amongst neighbors. We show how rainfall induced phenology changes may have impacted competition outcomes between species pairs due to differences in their response to reduced water availability. More research on the effects of phenology changes on coexistence and the community level repercussions they cause due to changes in competitive interactions is essential for mitigating the impacts of climate change.