The influence of substrate type and depth on establishment of five common green roof plants has been evaluated by researchers from the Department of Horticulture at The Pennsylvania State University.
Plants suitable for extensive green roofs must tolerate extreme rooftop conditions, and the substrates in which they grow must meet both horticultural and structural requirements.
Christine E. Thuring, Robert D. Berghage, and David J. Beattie hypothesized that early drought is more harmful for plants grown in shallow rather than deeper substrate depths.
They also theorized that plants that survived early drought conditions would produce less shoot biomass than those subjected to late drought.
The results showed that the stonecrops performed well under most conditions, although tasteless stonecrop was stunted by early drought.
Ice plant performed erratically and, along with maiden pink, poorly in drought. During drought, the herbaceous perennials had the fewest survivors in the expanded shale.
The three most resilient species used in the study-saxifrage pink, white stonecrop, and tasteless stonecrop-always produced more shoot biomass with increasing substrate depth, regardless of water availability.
But saxifrage pink had an attractive appearance and persistent flowering habit, making it an excellent choice as a green roof plant.
"This experiment revealed the variability among drought-tolerant species to various treatments, as well as the different plant responses to substrate type during drought", concluded the scientists.
The study appears in HortTechnology.