Ornamental Grasses Tolerate Cyclical Flood, Drought, and Submergence During Stormwater Management, but Conditions and Survival Vary by Species

Abstract

Perennial ornamental grasses are often recommended for rain gardens, but few data support their use. We conducted two experiments to evaluate the ability of ornamental grass cultivars to grow while subjected to cyclical flooding, submergence, and drought typical of rain gardens. Our objectives were to determine the effects of cyclical flood and drought (Expt. 1) and submergence depth and duration (Expt. 2) on grass growth and survival. Seven cultivars were evaluated during greenhouse trials, including Pixie Fountain tufted hairgrass [Deschampsia cespitosa (L.) P. Beauv.], Northwind switchgrass (Panicum virgatum L.), Red October big bluestem (Andropogon gerardii Vitman), Purpurascens Chinese silvergrass (Miscanthus sinensis Andersson), Blue Heaven® little bluestem [Schizachyrium scoparium (Michx.) Nash], Blonde Ambition blue grama grass [Bouteloua gracilis (Kunth) Lag. ex Griffiths], and Karl Foerster feather reed grass [Calamagrostis ×acutiflora (Schrad.) DC]. During Expt. 1, grasses underwent four cycles of flooding duration (2 days or 7 days) followed by drought (drying to volumetric soil water contents of 0.14 or 0.07 cm3·cm−3). During Expt. 2, grasses were cyclically submerged at 15 or 30 cm above the soil surface for 2, 4, or 7 days, followed by floodwater removal and drainage for 2 days before being resubmerged. Cyclical submergence continued until the 7-day submergence treatments completed four cycles. Both experiments were replicated in a full factorial randomized complete block design. Controls were included in both experiments. Plants were measured to determine plant height, shoot count, visual damage rating, shoot dry weight, and root dry weight. Floodwater chemistry and soil reducing conditions were measured during Expt. 2. Chinese silvergrass and switchgrass survived cyclical soil flooding/drought and submergence for 7 days at a depth of 30 cm while maintaining acceptable foliar damage. All grasses survived cyclical flood and drought when the soil volumetric water content was maintained at 14%, suggesting they can withstand periodic soil flooding as long as the water is not too deep. As water depth and duration increased from 4 days to 7 days, little bluestem, blue grama grass, and feather reed grass experienced significant foliar damage. Tufted hair grass and big bluestem experienced significant foliar damage when submerged for 2 days. Our results showed that perennial ornamental grasses can tolerate cyclical flood and drought and periodic submergence, but that plant conditions and survival vary, which can inform strategic plant placement within rain gardens, bioretention basins, and other stormwater management systems.