Agroforestry systems have received a significant attention in recent years and can be considered as a potential strategy in agricultural production to respond to worsening climatic conditions. The decision-making process for farmers to design and implement agroforestry systems is complex due to time-consuming processes of planting, growing and management of trees, as well as the long-term impacts on the field and its productivity. The shading of the arable land by trees is a core issue and should be reduced through a north-south orientation of the tree rows. However, this orientation is often in conflict with other criteria. In order to consider future shading from different tree row orientations into the design process, the modelling tool “ShadOT” was developed. This tool can simulate tree growth and analyses spatial shading over variable time periods by using only a limited number of parameters. This tool was programmed exclusively with open source software and can therefore be easily extended. It offers an ideal platform for testing different agroforestry designs due to its simple approach and minimal parameterization. Two different designs (north-south and west-east orientation) were tested for a field and differences in the temporal and spatial distribution of shaded areas are presented.