Miscanthus×giganteus (Greef et Deu.), a perennial rhizomatous grass, native of SE Asia, has been trialed Europe-wide as a potential bio-energy crop. Plant growth models have been developed to match previously reported field experiments. These models have been used to extrapolate Miscanthus yields to other environments. Although the models use similar process descriptions, the parameters used to match the experimental data vary from site to site. This paper describes the development of universal process descriptions that use genotype-specific parameters to predict yields in a wide range of environments. Using these, we develop a new model, MISCANFOR, from an existing model MISCANMOD by improving process descriptions for light interception by the canopy and the impact of temperature and water stress on radiation use efficiency. Genotype-specific process descriptions for plant growth phase, photo-period sensitivity, thermal time, temperature dependant radiation-use efficiency, drought and frost kill predictions, nutrient repartition to the rhizome, and moisture content at harvest are added. Predictions made with MISCANFOR are compared with MISCANMOD for 36 experimental data sets for a wide variety of soils and climatic conditions in Europe. MISCANFOR matches field experiments with an r2=0.84 compared with 0.64 for MISCANMOD, building confidence that the new model will be better able to predict Miscanthus yields for other areas and future IPCC climate scenarios. This model has identified photoperiod sensitivity in addition to drought resistance and frost tolerance as parameters for crop improvement to extend the range of climatic conditions under which this crop can be grown economically.