Metric-based plant selection for roadside rain gardens in cold climates

Plant selection is critical for the performance and long-term functionality of NBS. However, selecting suitable species remains challenging due to factors such as the need to balance multiple performance criteria. This study addressed this gap by proposing a structured decision-making framework for roadside rain gardens (RGs) in cold climates, based on three objectives, thirteen criteria, and sixteen quantitative metrics scored on a 1–5 scale. The framework was tested on five plant species commonly used in RGs in Norway to demonstrate its application and assess data availability for the metrics. Results showed that the evaluated plant species exhibit different strengths across objectives: for instance, Bolboschoenus maritimus excelled in plant procurement and establishment support, while Iris pseudacorus scored highest in functions of interest. Consequently, a combination of high-performing species was recommended for RG vegetation design. While the framework was successfully applied, limited data for some metrics required assumptions, highlighting the need for more comprehensive species-specific databases. Given the critical role of plants in the success of NBS, it is recommended that the framework be integrated into official RG design guidelines, with criteria tailored to local conditions.