Species arrival sequence in new habitats impacts plant community development. This 'priority-effect' is documented, but mechanisms by which early arriving plants dominate future communities are less clear, complicating our ability to predict community assembly under future climate warming and assess invasive species threats. This is particularly important for ecosystems that are vulnerable to invasive species, such as those of the Antarctic Peninsula. To test how phenological differences and arrival order affect community composition of invasive plants, we simulated maritime Antarctic climate conditions, and a warming scenario. We established monocultures of six species potentially invasive to the Antarctic Peninsula (three forbs and three grasses), which exhibit a range of germination times ranging from 22 and 68 d, and a mixed community of all species. Before entering a simulated winter, half of each monoculture (n = 10) received the full seed mixture while the other half received seeds of their respective starting species. During the following simulated growing season, we quantified if the community composition was influenced by arrival order and whether species germination and growth responses differed from their monocultures and starting species. Community compositions differed across all starting communities and were typically dominated by the starting species. Phenological differences influenced individual and total biomass and plant height, but faster germinating species did not consistently dominate the final plant community. Forbs and grasses negatively impacted each other's biomass. Warming enhanced priority effects (more negative or positive). Phenological priority has ecologically relevant influences on community assembly, but its effect on plant growth is context dependent in terms of species and temperature conditions. In particular, our data suggest that phenological priority influences plant biomass and size while niche pre-emption affects seed germination. Future trajectories of polar terrestrial plant communities will depend on the arrival order of colonizing non-native plants and their germination rates.