Do plants matter? Determining what drives variation in urban rain garden performance

Green infrastructure, specifically rain gardens, are increasingly used to manage urban runoff. Rain gardens vary in design and composition for a mix of aesthetic and functional reasons. Due to this variability, key performance drivers are hard to identify. This study evaluated 100 vegetated rain gardens in Lancaster, PA across seasons to determine which aspects of rain garden design impact performance. Gardens varied in size, slope, plant composition, planting density, and soil characteristics. There were significant seasonal differences in both performance (as measured by infiltration) and garden characteristics. Soil water content, compaction, and electrical conductivity along with plant species diversity significantly impacted infiltration. Certain plant species - Vernonia baldwinii (Ironweed), Nepeta cataria (Catmint), Itea virginica (Virginia Sweetspire), Rudbeckia sp. (Coneflower), and Eragrostis pectinacea (Purple Lovegrass) were present in high abundance and found to be drivers of performance. The results of this study demonstrate the diversity of factors that influence rain garden performance and highlight the importance of aligning soil and plant characteristics with specific outcome goals.