2017 ASHS Annual Conference

As urban areas expand, permeable surfaces are replaced with buildings and paved surfaces producing large quantities of stormwater runoff. Runoff contains sediment, nutrients, and chemicals that may harm surface waters. Rain gardens are used as retention basins to allow stormwater to infiltrate and evapotranspirate while removing pollutants. The rain garden environment is unusually challenging, because plants depend on seasonal precipitation and are subjected to alternating periods of flooding and drought. Although rain gardens are designed to drain within 48 hours, frequent rainfall, design issues, or lack of maintenance may result in a longer saturation period. Sedges (Carex spp.) are frequently recommended for rain gardens because of their tolerance of fluctuating water levels. However, scientific studies to support such recommendations are scarce. Seven sedge species native to the north central United States, yellow fox sedge (C. annectens E.P. Bicknell), plains oval sedge [C. brevior (Dewey) Mack], Gray’s sedge (C. grayi Carey), porcupine sedge (C.hystericina Muhl. ex Willd.), palm sedge (C. muskingumensis Schwein.), Pennsylvania sedge (C. pensylvanica Lam.), and Sprengel’s sedge (C. sprengelii Dewey ex Spreng.) were tested in a greenhouse trial. Treatments consisted of two flood periods, two or seven days, followed by one of three drought setpoints measured by volumetric water content thresholds of 0.05, 0.10, or 0.15 m³·m^-3 . All combinations of treatments were tested and each plant was subjected to a minimum of four flooding and drought cycles. Data collected included shoot count, visual damage rating, and dry weight of shoots and roots. The experiment was replicated three times. Within a species, shoot counts for porcupine sedge, palm sedge, and Pennsylvania sedge were significantly reduced for the 0.05 m³·m^-3 drought setpoint compared to the 0.10 and 0.15 m³·m^-3 drought setpoints. Across all sedge species, shoot mass and root mass were significantly reduced for the 0.05 m³·m^-3 drought setpoint. Within a species, root mass of Pennsylvania sedge was significantly reduced for the seven-day flood treatment compared to the two-day flood treatment. Plants subjected to the seven-day flood treatment exhibited significantly increased shoot mass compared to the two-day flood treatment. Plains oval sedge showed a significantly higher total biomass than porcupine sedge, palm sedge, Pennsylvania sedge, and Sprengel’s sedge under all treatments. Overall, sedges are extremely adaptable to alternating flooding and drought cycles, but they may require supplemental irrigation during times of drought.