Climate change poses a potent and immediate threat to global biodiversity. Increasing global temperatures have severe effects on the ecological dynamics of organisms. While temperature is a key factor in influencing the phenology of organisms, other environmental factors also play crucial roles. Rhododendron arboreum Sm. (R. arboreum) is an important keystone species of the Himalayan ecosystems with several ecological and economic benefits. Here, we focus on the impact of various factors that influence the flowering phenology of R. arboreum in the North-Western Indian Himalayan region (Chakrata Forest Division, Uttarakhand). Comparing with previous herbarium records, we observed a shift in the onset of blooming in R. arboreum. The results showed a significant association with age, elevation, slope aspect, and sunlight on the flowering phenology of the species. We infer that understanding the cumulative effect of biotic and abiotic parameters is crucial for understanding the species’ phenology. In light of the ongoing warming, this study has potential application by park managers in designing conservation strategies in the Himalaya, one of the least studied and most threatened biodiversity hotspots of the world.