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botanical gardens which will be used alongside information on plant traits and site conditions to answer questions related to the consequences of global change: A. What is the variation in plant phenology in herbaceous species across the growing season and in response to changes in climate? B. How can plant phenology be predicted from species' trait composition, provenance, position and extent of the distribution range and species' phylogeny? C. What are the implications of this variation with respect to species performance and assembly, biotic interactions (e.g. plant-pollinator interactions) as well as ecosystem processes and services under changing land-use and climate? 3. Here, we lay out the development of a straightforward protocol that is appropriate for monitoring phenology across a vast diversity of growth forms of herbaceous species from various habitats and geographic regions. 4. In order to focus on a key number of stages necessary to capture all aspects of plant species phenology, we analysed associations between 14 phenological stages. These data were derived from a two-year study on 199 species in four German botanical gardens. 5. Based on the relationships of the phenological stages, we propose to monitor three vegetative stages ("initial growth", "leaves unfolding" and "senescence") and two reproductive stages ("flowers open" and "ripe fruits") to fully capture herbaceous species phenology.