Rooting Volume Impacts Growth, Coverage and Thermal Tolerance of Green Facade Climbing Plants

Green facades can provide cooling benefits through the shading of walls, evapotranspiration, and insulation. These benefits depend on good plant coverage and tolerance of heat stress. This requires sufficient rooting volume for plant growth and an adequate supply of moisture. On high-rise buildings, plants can be constrained by small rooting volumes due to engineering weight limits and cost. We assessed effects of rooting volume (21, 42, and 63 L) on the growth and coverage of Akebia quinata and Pandorea pandorana and leaf stress (chlorophyll fluorescence) in response to increasing air temperatures. We showed that 42 and 63 L rooting volumes significantly increased early plant growth and the percentage wall coverage for both species. Specific leaf area was significantly greater when grown in 63 L compared with 21 L. Shoot/root ratio did not change with rooting volumes. Regardless of rooting volume, higher air temperatures on west-facing aspects led to afternoon leaf stress. In practice, for each cubic meter of rooting volume, 21 m(2) (P. pandorana) and 10 m(2) (A. quinata) canopy coverage can be expected within six months.