Urban areas serve as important habitats for many taxa worldwide, with biodiversity potential often arising from the heterogeneous mosaic of greenspaces and the many different drivers that shape species assemblages. This also includes highly anthropogenic green infrastructure such as vertical greening systems that are gaining more attention as cities densify. Yet, their potential for different types of vegetation, including spontaneous species, and how this associates with the occurrences of different pollinator groups, remains largely unexplored. We therefore assessed (a) the vegetation, (b) diverse pollinator groups, and (c) their association on 24 pre-existing and newly established green wall systems in the metropolitan region of Stuttgart, Germany, over six sampling periods, including different seasons and years (N = 108). Our data demonstrates a high variety in the use of cultivated plant species and that spontaneous species, as well as species from near-natural planting design, can add variety to vegetation composition. Overall, we identified 200 plant species and mapped at least one pollinator group during each site visit, with a maximum of 75 individuals counted during a mapping in early summer. Based on the results of generalized linear models, we determine that certain pollinator groups associate with plant species richness (wild bees, bumble bees, hoverflies) and/or flower cover (bumble bees, honeybees, wasps). For some pollinator groups, the season or the greening system was also relevant. In conclusion, our study demonstrates that vertical greening can contribute to biodiversity support in dense cities if such strongly designed spaces consider specific environmental characteristics.
