FSPM are getting popular, open to a wide range of application and implemented in numerous simulation software or platforms. However, those seldom cover the field calibration aspects. We propose here a simple tool, StemGL, limited to single-stemmed plants, covering both calibration and simulation aspects of biomass production and allocation. Based on GreenLab model assumptions, the tool implements stochastic simulation capabilities; it offers virtual insights, and also presents field data comparisons. The application is delivered with a set of examples, with virtual plants to analyze and simulate, and real field plants with their parameters to retrieve.