For organic vegetable growers, combining long rotations involving a high level of plant diversity with intercropping can bring economic and ecological benefits but often increase management complexity and workload. To support the decision making of farmers facing such challenges, the research-action objective of the MESCLUN programme is to develop a web application based on the innovative computer technologies of knowledge graphs and semantic web. In this French transdisciplinary project, we articulate methods and frameworks from different fields (agronomy, economy, design, knowledge and computer engineering) with expertise of agricultural practitioners (organic growers, advisors, teachers, organic farming students). Through an iterative and participatory approach based on co-innovation workshops in 4 contrasted regions of France, we design, develop and test web app prototypes to help farmers to appropriate systemic thinking, explore and assess their “own” solutions in the organisation of complex organic vegetables systems. We will present functionalities/interface of the first web app prototype. We will for example show how the web app can help growers to plan their crops in space and time considering contrasted fertility and plants health strategies as well as marketing requirements. We will also illustrate how different simulations can be assessed from a socio-economic perspective (workload and income). Based on those first results, we will examine the specificities, added value and blind spots of our web app compared to other decision making tools in the organic agricultural sector. To feed a more general debate, we will provide critical discussion points on the potentialities and limitations of innovative digital solutions to support decision making in complex organic farming systems.