The demands on urban tree substrates are diverse, whereby structurally stable/stable systems are sought that can guarantee tree vitality for as long as possible. In this context, the test design conceived at the Schwamendingen enclosure serves to compare three different substrate compositions. The aim is to determine which substrate composition proves to be the most suitable. This substrate composition is to be used as a substructure for the joint path at the future enclosure and thus guarantee the root space even under heavy traffic. The substrate properties and their effect on three different tree species were observed over a period of four years. Ideally, the source materials for the substrates should be available locally, in consistent quality and sustainably. At the enclosure in Schwamendingen, three mixtures (substrate construction method 2 of the FLL, Stockholm substrate adapted, Stockholm substrate) were compiled on the basis of existing structural substrates and planted with trees (Ulmus ‘New Horizon’, Salix alba ‘Liempde’, Quercus frainetto ‘Trump’). Measurements of the development of the root systems, assessments and measurements of sap flow (i.e. transpiration) were carried out on the experimental trees. The trees were dug up again at the end and measured.