The ever increasing amount of data gathered by more growers in more years offers possibilities to add value. Therefore—for interested parties and stakeholders—a common and controlled vocabulary of the potato domain that describes concepts, attributes, and the relations between them in a formal way using a standardised knowledge representation language is being developed: a potato ontology. The advantage is that all possible stakeholders will be able to understand the data expressed by this ontology and that software applications can process them automatically. It will also allow the application of advanced numerical techniques that may help to uncover previously unknown correlations. This version of the potato ontology aims at the domain of processing potatoes in a setting of mechanised potato production where growers have access to automated decision support systems and exchange data electronically. This paper describes the procedures to establish such an ontology where competency questions formulated by stakeholders and potential users take a central position. The potato ontology formally describes “Concepts” or “Classes”. The three main classes are those used in crop ecology: Crop, Environment and Management. Classes, e.g., biocides are a subclass of agro-chemicals, and in turn have a subclass Fungicides. The ontology also describes the “Properties” of classes, e.g., agrochemicals are produced synthetically in a factory; biocides are used to protect crops and fungicides to control fungi. The ontology also describes the “Attributes” (properties) of the concepts, e.g., all agrochemicals have attributes such as dose and time of application and mode of application. “Restrictions” may be that a particular chemical can only be applied with a certain type of equipment, or its application is restricted to a certain period or dose. The ontology also features “Instances” which are the individual data such as a particular herbicide treatment with values for field, time, dose, active ingredient, trademark, mode of application, which equipment operated by whom. The standardisation language used is the “Ontology Web Language”.