Unfortunately, the strategy of plant selection is not well understood in design and architecture where aesthetics dominate, according to John Rayner, senior lecturer in urban horticulture, Burnley Campus, University of Melbourne.
“Many design professionals will choose flowers for façades and won’t let them grow first,” Rayner said. “They need to choose plants that will meet the functional outcomes for the site – plant selection is crucial to this process."
For example, Rayner believes air plants such as the Tillandsia, which does not require soil and can absorb moisture through its leaves, provide a wonderful aesthetic for cities, but to reap maximum cooling benefits, the key is to go for size through trees and large green leaf vegetation.
Green façades are a testament to this as reported in a recent study titled New Green Façades as Passive Systems for Energy Savings on Buildings, which states, "Green façades and green walls act basically as passive systems through four mechanisms; the shadow produced by the vegetation, the insulation provided by vegetation and substrate, the evaporative cooling through evapotranspiration, and finally the barrier effect to the wind."
The next consideration is sunlight which, according to Rayner, is crucial to the survival of a green façade but is woefully underestimated. He noted that most façades are being developed in dark inner city canyons, which can further compromise plant growth. As a result, shading and location should also be a decision factor when selecting plants.
So when making the decision to build a façade, who should be involved?
Perhaps counterintuitively, Rayner believes landscape architects are not the best people for this job but commends architects on 'getting it'.
He cited maintenance concerns, noting that some plants can be technically difficult to install and maintain, with access, irrigation and pruning all potential obstacles. He added that the industry is just now learning what does and does not work and the technologies that help green facades survive and thrive while remaining distinct.
The key consideration, he said, is soil substrate. “Most of the research demonstrates that the container sizes are inadequate for longevity,” he said. “The challenge is not now, it’s in 10 to 20 years … The best thing to do is get these plants in the ground with a good quality soil based planting location."
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