sewerage and manage stormwater. The Royal Botanic Gardens Victoria has used them in their Rain Garden to filter and make use of urban stormwater runoff. In filtration wetland projects, cannas have been shown to be more effective than the traditionally used Australian native plants such as Carex and Juncus species because of their unique range of functional attributes. Cannas: • are tolerant of drought and dry soils, • are tolerant of water logged and saturated soils, • are tolerant of most soil types from well draining sand to boggy clays, • are adaptable to low and high nutrient loads, • can remove high levels of nutrients by harvesting and removing the leaves each year at pruning time, • can reduce total suspended solids and nitrogen in wastewater including sewerage, and • have fast growth rates One of the keys to their success in waste water treatment systems is that they provide an ornamental quality to the landscape which native plants often can’t match. For those who prefer form over function, this often makes them more popular with locals and even politicians
The Floating Canna Island in the Ornamental Lake at the Royal Botanic Gardens Melbourne.
because they look good while doing their job. This is important when trying to sell and promote a new residential development site, high profile industrial site or a public recreational lake treatment system. Never underestimate the political value of a good photo opportunity in front of colourful plants when trying to promote a potentially boring water filtration project. The Floating Canna Island was a trial to reduce nutrient levels and reduce the incidence of blue‑green algae outbreaks while providing an ornamental and heritage landscape feature that’s very popular with visitors. It’s mostly made of recycled materials including a floating bamboo frame which has netting underneath with coir matting mulch to protect the rhizomes and provide support. Someone once said that good design is a fusion of form and function which the canna island design certainly has. Perhaps we’ll see this solution in Bendigo’s recreational lakes and billabongs in the future.
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the botanic gardener | ISS 46 November 2016