Models simulating dry matter production have been developed for a large number of greenhouse crops during the past decades. This paper describes how plant-nutrient relationships can be incorporated in a model for greenhouse crops, with sweet pepper as an example. Based on climatic data, the model simulates the growth of plant organs, transpiration, water uptake and uptake of the various macro nutrients. A mechanistic photosynthesis-driven model is used to simulate dry matter production. For each plant organ its required concentrations of the various macro nutrients are calculated, which depend on the ontogenetic age of the organ. The required nutrient uptake is calculated from these required concentrations and the dry weights of the organs. If there is no limitation in availability at the root surface the actual uptake will equal the required uptake. When the root system cannot fulfil the demand, uptake will be less, plant nutrient concentration will drop and crop production is potentially reduced. The model was tested on data from two different climatic regions (France and Spain). The model was also used to show some effects of the greenhouse climate on water and nutrient uptake. The rate of water uptake per unit radiation as well as the EC of the water taken up by plants was shown to vary considerably. Finally, the utilization of the model in an integrated control and monitoring system is discussed