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The new Australian garden grown on walls and roofs, not in the ground 22 May 2012

The traditional concept of the Australian garden could soon change considerably thanks to a Rural Industries R&D Corporation-funded research project that has identified a number of hardy native plants that can readily grow on the walls and roofs of buildings.

Dubbed “vertical gardens”, the concept involves setting up slim-line growing beds on building walls and also on rooftops, where the plants grow in specialised soil and are watered using a drip irrigation system.

The research project found that there were social, environmental and economic benefits from growing plants on walls and rooftops.

One of the project’s chief researchers, Dr Melinda Perkins from The University of Queensland said that the greatest benefit of a vertical garden is its ability to block heat.

“Apart from being attractive, these gardens can reduce the need for air conditioning in warm weather by shading and buffering buildings from heat,” Dr Perkins said.

“Temperature reductions of up to 17 degrees celsius were achieved inside prefabricated metal buildings that incorporated living walls and rooftops.

“In the built environment this can lead to very significant reductions in energy demand for air conditioners.
“The technology used to grow the plants is widely adopted in Europe, particularly Germany, and is becoming more popular in the USA and Singapore.”

The research project identified six native plant species for green roofs and seven for green walls that displayed traits suited to Australia’s harsh sub-tropical environment.

“To be suitable the plants need to have a strong, shallow root system, provide good vegetation cover, be pest and disease hardy, and be tolerant of wind, drought and high temperatures,” Dr Perkins said.

“On the other hand, species prone to become a weed problem or which display aggressive growth rates should be avoided.  Also, where sites are accessible to the public, plants with thorns or which are poisonous to humans are potentially unsuitable.”

Perennial species - those that do not have to be replanted every year - that form a mat or clumps were shown to be the best for long term coverage.

In terms of performance, the natives ‘Creeping Myoporum’ and ‘Winter Apple’, and the exotic ‘Tasteless Stonecrop’ displayed good survival and coverage as an extensive green roof species. For green walls, ‘Bulbine Lily’, ‘Cockspur Flower’ and ‘Silver Plectranthus’ performed well in terms of their growth and survival.

Future research could look into how green roofs and walls could be included in building sustainability incentive schemes, such as the Green Building Council’s ‘Green Star’ rating. The report ‘Living Wall and Green Roof Plants’ is available for free from www.rirdc.gov.au

Media enquiries:
Damon Whittock – RIRDC Public Affairs Manager – 02 6271 4175 or 0458 215 604