The use of green roofs as a self-reliant and low-input technology emerged in Europe, Scandinavia and the UK, where climate conditions are favourable for maintaining green roof vegetation without irrigation. But how useful is this environmentally-friendly technology in more hostile climates?
The application of green roof technology has become more common in the central, northwestern and eastern USA, and is now being employed across the southern USA as well. However, there is little research in the literature that evaluated plant survival on unirrigated green roofs in subtropical climates that experience frequent drought and heat stress. A new paper in AoB PLANTS summarizes the results of a study of plant establishment on a modular green roof in south-central Texas. Fifteen plant species were field tested in green roof modules on a four-storey building in College Station, Texas, with irrigation limited to the first several weeks of establishment. Climate data, plant growth and species survival were measured over three growing seasons.
The establishment and survival of several plant species without any mortality suggests that irrigation limited to the first few weeks after planting may be an effective approach on green roofs in spite of the more challenging climatic conditions in the southern USA. Since the climate in south-central Texas had been consistently drier and warmer than normal during the study period, longer-term research on these species is recommended to expand knowledge of establishment requirements for these species under a wider range of conditions, including wetter than normal years.