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Australian Plants for Green Roofs and Walls:

Green roofs and living walls offer great environmental, economic and social benefits. They reduce urban heat island effects, reduce energy demands and attendant CO2 emissions as well as improve wellbeing and productivity of residents. Today, urban buildings are continuously looking for ways to integrate growing plants while maintaining the structural integrity of the building.

However, according to a 2012 report called Living Wall and Green Roof Plants for Australia, “a lack of proven plant species suited to Australia’s harsh climate is one barrier to the uptake of green infrastructure in this country”.

Because of this, the Australian government developed a plant selection matrix tool to identify plants suited for green roofs and exterior living walls in subtropical Australia. The information in the report is useful to growers in the nursery industry and to green infrastructure suppliers and design professionals.

The report found that plant species for green infrastructure in Australia ideally need to “withstand stresses of high temperature, wind and water deficit while providing good vegetation cover”.

The climate in the country is expected to become even harsher with climate change. “Experts predict reduced rainfall overall and increasingly extreme climate events, such as droughts, storms and cyclones. In this context, the ‘Achilles heel’ of a potentially vibrant green infrastructure industry in Austrlaia is the lack of proven performance for appropriate plant species.”

Based on the selection process, the native Myoporum parvifolium (Creeping Myoporum), Eremophila debilis (Winter Apple), and Sedum sexangulare (Tasteless Stonecrop) showed the greatest survival and coverage on an extensive green roof.

“Growth rates of the three species were higher than expected with full coverage achieved 21 weeks after transplanting,” the report said. The report also found that covering roofs and walls with greenery greatly reduces maximum temperatures of the internal roof and wall surface.

Prior to this report, there has been limited information on the suitability of Australian native plant species for extensive roofs and external green walls in the country’s northern regions. “This general limitation plus a specific lack of ‘local’ data to quantify the claimed benefits of green infrastructure have hindered its uptake in these regions.”

The report has taken a step in the right direction to address these hindrances. Still, the report recommends that a long-term evaluation of a wider range of plant species, substrate formulations, and irrigation regimes is needed to support Australia’s move towards green infrastructure. This is especially needed in the warmer northern regions.

“While there are currently few investors in this new and emerging industry, its growth in the subtropics will likely continue to generate interest and needs in the medium to long term.”

Meanwhile, several states around the country have started their own efforts to turn buildings green.

Queen Street Mall in Brisbane will have a $4 million renovation that includes changes on Jimmy’s on the Mall. The design will include a garden on the top floor and living green walls.

In Victoria, the launch of the new online resource by University of Melbourne research will see buildings across Melbourne turning green. The Growing Green Guide “will help building owners, planners, designers, developers, renovators and homeowners include green plant roofs, walls and facades into their buildings to help manage the impact of a changing climate on city living”.

The guide has step-by-step advice and examples on how to incorporate green roofs, walls and facades that will suit the Victorian climate. The university previously established “purpose-designed” green roofs to support the pioneering research of the Green Infrastructure Research Group and as a demonstration of how green roofs can be created. The Burnley Living Roofs is the first of its kind in the country.

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