Performance evaluation of native plants suited to extensive green roof conditions in a maritime climate

Assessing plant species performance on extensive green roofs can inform about and improve green roof functioning, aesthetics, longevity and the diversity of plant palettes available for the green roof industry. In this study, we evaluate survival, cover, roof cooling and stormwater retention properties of 15 plant species native to coastal regions of Atlantic Canada in extensive green roof monocultures. After a complete growing season (May–October 2009), all but one species had greater than 80% survival, and 10 species reached greater than 90% groundcover. Over the growing season, the top performing species reduced roof surface temperature by an average of 3.44 °C and increased solar reflectivity by 22.2% over the growing-medium only controls. Moreover, the best species retained 75.3% of experimentally added stormwater. Our results demonstrate that several species (mainly graminoids) performed better than creeping shrubs and forbs for most functions, although significant variation existed within life-form groups.

Research highlights▶ Out of 15 native species, all but one had >80% survival after the first year. ▶ Best species reflected 5% more solar radiation than growing medium-only controls. ▶ Roof surface temperature was reduced 3.44 °C by the best species over the controls. ▶ 75.3% of all experimentally added stormwater was captured by the best species. ▶ Great variation in performance within life-form groups.