Identification of Landscape Plant Species for Use in Rain Gardens

As urbanization increases, so does the volume of stormwater runoff entering native waterways.  This runoff often carries excess nutrients and other pollutants, and the volume may overwhelm natural waterway capacities.  Rain gardens are a Low Impact Development (LID) strategy that can be used to trap and filter runoff.  Proper plant selection is critical for the success of rain gardens since they absorb water and nutrients and provide aesthetic value to a functional garden.  Although many recommendations for rain garden plant species exist, few have actually been critically evaluated for tolerance of the fluctuations in hydrology that occur in a rain garden.  Plants in a rain garden may experience inundation for up to 48 hours followed by long periods with no additional irrigation.  By exposing plants to repeated flood-drain cycles in a controlled environment, it is possibly to identify plants suitable for use in rain gardens.  Previous and current research has directly identified three grasses, four evergreen shrubs, five deciduous shrubs, and two herbaceous perennials that are tolerant of expected rain garden conditions.  Conversely, research identified two species that were not tolerant despite appearing on many recommended lists.  Plants tolerant of rain garden conditions typically have vigorous root growth and often can adjust root system architecture to minimize effects of inundation.  Additionally, plants with larger root systems at the time of planting are more likely to establish and survive in these conditions.  Although plants often exhibit reduced canopy dimensions when flooded, visual quality is typically not compromised.  Finally, it does not appear that exposure to flooding during production imparts any additional flooding tolerance once in the landscape.