For its unpredictable weather, Melbourne is known as the Australian city that can experience four seasons in one day: hot and blustery one minute, chilly the next. It is a punishing and therefore perfect environment for ecological artist Lloyd Godman to test his theories on beautifying cities with so-called living building materials. Suspended above Melbourne's central business district are Godman's super-sustainable sculptures. The product of 10 years of experimentation in his North Melbourne home, they are living, rotating artworks created by entwining bromeliad plants around shapely steel structures (which are usually salvaged pieces such as old woks or bicycle parts). The eight sculptures in Airborne, unveiled at the Sustainable Living Festival this year and on display at least until April, demonstrate what Godman believes is the next generation of green building design. Unlike vertical gardens and green roofs, which use conventional soil-rooted plants, these require no artificial life-support system. Bromeliads survive without the need for soil or irrigation by taking nutrients and moisture from the air. Apart from a biannual trim, they require no maintenance and are among the hardiest plants on the planet. Another advantage is their weight. They weigh just 2kg to 3kg per square metre compared to 50kg to 60kg per square metre for soil-based or vertical and roof gardens. "Air plants are [also] perfect in terms of their ESD [environmentally sustainable design] qualities," says Stuart Jones, a structural engineer from Point 5 Consulting. And yet they bring many of the benefits of conventional urban greening: providing screening, beautifying streetscapes, filtering the air and cooling buildings. They are also cost-effective. "The Tillandsia [the genus used in Airborne] replicate asexually, so air gardens can actually generate a return whereby the plants are harvested to place on another building," Godman says. He envisages his suspended works providing shade for hot, exposed plazas. They are also visually appealing. "When the air gardens rotate they create intricate animated shadows on the ground," he says. He is also experimenting with what he calls air curtains. This utilises the concept of a vertical plant wall where sections fixed to a sliding track can be moved to provide shade or privacy as needed. "Unlike vertical gardens, which are opaque, these screens are like lace, and you can still see outside through them. When they are in flower, the screen is very beautiful." Godman is also developing a proposal for a design that will harness the tides. This concept, which he sees as ideal for a harbour city such as Hong Kong, uses a float and lever system to move an air curtain up and down the facade of a building with each change of tide. "We worked out how to take one metre of tide and move the garden by five metres - all you need is access to the sea," he says. Another idea is to design the plantings as a QR code, which could take the viewer directly to a business owner's website. Godman has been described as one of a new breed of environmental artists whose work is directly influencing green building design. His experiments demonstrate how, by removing the constraints of life-support reliance, new possibilities can emerge. Jones believes that the sky's the limit for Godman's air gardens. They can survive and thrive in Melbourne's hostile climate (remaining safely tethered during recent winds of more than 140km/h), span great distances without the need of base support and take sustainability to new heights. As these models can hang like a banner, he is also excited about their potential to be used as staggered layers, adding texture to building facades and thus beautifying cities. "Planter boxes on balconies are not green or sustainable, as they require structural elements to support them, thus adding to the greenhouse cost of a building," Jones says. "We should be trying to create a carbon sink, not a carbon footprint - and these designs achieve that."