Evaluation of Three Soil Blends to Improve Ornamental Plant Performance and Maintain Engineering Metrics in Bioremediating Rain Gardens

This research project explores the performance of soils intended to support ornamental plants serving an ecological benefit within bioremediating rain gardens. Three plots of identical plantings were installed in autumn of 2015 into three different planting media in Northeast Ohio, USA. A control soil blend was tested against two experimental soil blends in the field under natural conditions for 3 years to explore any potential differences in overall plant performance. The control planting soil was created following current Ohio Department of Natural Resources specifications for rain garden planting soils which consist of no less than 80% sand and no more than 10% clay by volume. Test soil blends incorporated lightweight expanded shale to combat the potential negative effects of high sand soils for plants (i.e., high matric potential) while maintaining required engineering benefits (i.e., fast infiltration rate coupled with good physical, chemical, and biological filtration). Our analysis suggests that incorporating expanded shales into bioremediating gardens as a replacement to high sand content can maintain all engineering specifications and may increase survival rates of plant life beyond rates currently found in high sand content rain gardens. Survival rate for plants in the control plot was at 48.3% while experimental plots one and two were 96.5% and 75.8% respectively. The research team suggests that these increased survival rates could contribute to more widespread adoption and implementation of stormwater management practices, especially small-scale, interconnected rain gardens in the urban environment as designated by low-impact development standards.