Phenology can contribute to many scientific disciplines from climate change, biodiversity, agriculture and forestry to human health. The knowledge of timing of phenological events and their variability can provide valuable data for planning, organizing and timely execution of certain standard and special (preventive and protective) agricultural activities that require advanced information on the dates of specific stages of crop development. Mathematical models are the basic tools to predict the timing of phenological events. There are two types of phenological models: physiologically-based and statistical. Most of the existing models are statistical and serve to predict the onset of different phenophases according to the air temperature. These models are site- and species-specific and cannot be applied to a wide range of species and climatic conditions.