Screening Native Herbaceous Species for Rain Garden Applications Under Different Submersion Regimes

Rain gardens are increasingly implemented as Nature-Based Solutions for stormwater management, where vegetation must tolerate alternating wet and dry conditions driven by design-related drainage times. Despite the central role of plants, experimentally based guidance on species selection, particularly for locally adapted herbaceous taxa, remains limited. This study presents a controlled experimental screening of 13 native Italian herbaceous species to evaluate their response to two different submersion regimes. Plants were subjected to repeated short (1-day) and longer (3-day) submersion cycles and compared with a non-flooded control. Species performance was assessed through an integrated framework combining survival, growth responses, biomass allocation and visual condition. All species survived across treatments, indicating a general tolerance to transient waterlogging. However, interspecific differences emerged when multiple response variables were jointly considered. Several species not typically associated with prolonged inundation maintained high performance under longer submersion regimes, while some taxa from drier environments also showed resilience to waterlogging. The results highlight that tolerance to submersion cannot be inferred solely from habitat moisture affinity and that submersion duration represents a key design variable for rain garden design. This study provides a pragmatic, low-cost screening approach to support context-specific plant selection in temperate urban environments.