Significance Inconsistent results regarding the rate of change in spring phenology and its relation to climatic drivers on the Tibetan Plateau have been obtained in the past. We introduce and describe here an innovative approach based on tree-ring data, which converts daily weather data into indices of the start (and end) of the growing season. This method provides a unique long-term record of vegetation phenological variability over the period 1960–2014. This approach could further be extended to other forested regions of the world. Scaling up the analysis would provide additional information on phenological responses of terrestrial ecosystems to the ongoing climate change across the Northern Hemisphere.