Researchers from the Department of Horticulture at The Pennsylvania State University have published a study evaluating the suitability of five common plants featured on green roofs. Green roofs are typically associated with improved air quality, reduced stormwater runoff, and heat mitigation.
The study focused on North American green roof plant types. Two stonecrops, one ice plant, and two herbaceous perennials were planted in three depths (30, 60, and 120 mm) of shale and clay. Drought conditions were also analyzed: No drought, 2 weeks early drought, and 2 weeks late drought.
The stonecrops performed well under all conditions, although stunting occurred during early drought for the tasteless stonecrop. The ice plant performed erratically and poorly in any drought conditions. The herbaceous perennials had few survivors in shale.
The big winners of the study were saxifrage pink, white stonecrop, and tasteless stonecrop, with saxifrage pink setting itself apart even further by having an attractive aesthetic appeal as well as a persistent flowering habit.
Plant selection is not always something immediately considered when weighing the benefits of a green roof, and studies like this one are useful for facilities managers and owners considering a transition to a green roof.
The complete study is available at the HortTechnology web site
