Enchanted by a billabong

Melbourne-based landscape designer Phillip Johnson is in northern Scotland, rugged up against the icy wind.

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IT'S an unlikely scenario. Melbourne-based landscape designer Phillip Johnson is in northern Scotland, rugged up against the icy wind, sleet in his eyes, as a six-tonne rock dangles overhead from a crane. He's rehearsing building a very special, very large water feature, a billabong inspired by an Australian gorge, and precision is everything. It's all part of the meticulous planning that goes into building a show garden at London's world famous Royal Horticultural Society Chelsea Flower Show. Next month, Johnson is set to take his mission - and his billabong - to the heart of Britain's gardening establishment - and to the world.

"We shouldn't be using precious mains water for anything other than drinking," Johnson says. He has already built a strong name for himself locally as one of the leading exponents of sustainable landscaping. In his late 30s, he still exudes boyish enthusiasm for his work and is eager to spread the word, operating his landscape business with a creed to educate and inspire change in how we coexist with nature. Despite the grand scale of his vision, Johnson insists we can all make a difference, starting with small steps. "I'd love to inspire everyone to tackle even a little garden project to help make their garden more sustainable," he says. "It can be making a frog pond or starting a vegie garden or swapping the motor mower for a push mower."

He has inspired visitors to the annual Melbourne International Flower and Garden Show, winning the Ford Sustainability Award two years running and best in show in 2009. His gardens are all about tackling big issues: water management, biodiversity, habitat, resources and organic principles, but on an individual scale.

Billabongs are at the core of Johnson's designs - he has already created more than 1200 around Australia and they are key to his water management strategy. All water falling on a site is captured and channelled either to the billabong or to rainwater tanks, which then overflow to the billabong. Aquatic plants on the margins absorb nutrients, cleaning the water, and provide habitat for frogs, birds, insects and micro-organisms. These plants are adapted to periodic flooding and drying cycles, enabling the system to manage peak stormwater flows and long periods without rain. The billabong provides the water source for irrigating vegetable and fruit beds, bushfire defence and evaporative cooling. It can also serve as a chemical-free, natural pool for swimming or fishing, while the addition of rock waterfalls increases both the aesthetic and functional benefits. Johnson sources raw materials from within 100km of a site, favouring reclaimed and recycled materials. He uses native and indigenous plants, and creates mulches from existing site waste. Compost bins, solar power and chook sheds are also on the checklist.

Importantly, he creates gardens that are also beautiful and family friendly. Visiting his home in the Dandenong Ranges, it's apparent he lives true to his word, having created a magical garden that is both research lab and sustainable show property. It is solar powered and not connected to mains water; yet the excess water on site is stored in a series of tanks and Johnson's trademark billabongs so he can live comfortably in an area that is both drought affected and fire prone.

Next month, Johnson will showcase these ideas on the world stage in London. The stakes are high, as this year is the Royal Horticultural Society's 100th Chelsea Flower Show, an anniversary that will attract the best of British fanfare. But Johnson's triumph may well be Australia's swansong at Chelsea. Wes Fleming, of Flemings Nurseries, who sponsored eight years of show gardens, has announced this will be his last and no other sponsor has yet stepped forward.

But in a rare compliment, the organisers have offered Johnson the highest-profile site of the show. "It's an awesome sloping embankment on the main corner. At 24m x 12m, it's 50 per cent bigger than the normal flat sites, but we still only have the same build time of 17 days. The billabong is the soul of our design, inspired by water holes in the Kimberley Gorges, Grampians or Blue Mountains. This one makes mine at home look like a puddle."

And that's why Johnson did a mock build of his rocky gorge in Scotland, moving more than 300 tonnes of rocks into their perfect positions, testing how the water flows to a variance of 10mm, timing how long it takes to construct. Johnson was thrilled to source the glacial rocks, which came from a landslip and lay stockpiled for 15 years, gathering moss. They're as recycled and as local as he can get.

"We will be talked about," he predicts. "This is my dream come true and an opportunity to really push the boundaries and inspire the world about sustainable landscape design." But will the Brits "get it"? There's a certain traditional Chelsea style and Johnson's design may be viewed as too radical a departure. "I think they'll get the concept straight away," he says confidently. "They've had some years now of drought and water restrictions and their thinking is changing in response."

Perched on top of the gorge will be a studio building with a shape inspired by a waratah, designed by Dylan Brady, of Melbourne's Studio 505. Amid hopes that the Queen, a Chelsea fanatic, will visit the garden, the timber blades are optimised to her eye height, so she can have an uninterrupted view of all the garden elements. Constructed in Australia using reclaimed steel offcuts, it's ingeniously designed to break down to pack inside itself, minimising shipping space. A curved timber boardwalk uses certified sustainably sourced timbers and the site will be powered using Australian solar panels. Johnson also aims to only use water collected on site, including the roof of the adjacent BBC media facilities. The planting palette of waterwise Australian plants includes a twist on a native wildflower meadow, and features the sculptural forms of Queensland bottle trees (Brachychiton rupestris). "It's the most amazing thing I've ever built in my life," says Johnson, grinning.

Helen Young writes the Twig and Flora columns for Weekend A Plus. To join her 2013 garden tour of Italy and the Chelsea Flower Show for The Australian, departing May 5, see travelrite.com.au

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HOW TO BUILD A FROG POND THE PHILLIP JOHNSON WAY

1. Choose a spot with both sun and shade, but not directly under a tree as some leaves can poison water.

2. Dig a hole with gently sloping sides. A flat bottom will allow for potted water plants. Surround the pond with a shallow mound.

3. Use damp sand to line the hole, then lay pond liner, enough to cover the surrounding mound.

4. Use rocks to anchor the liner and dress the edge, leaving spaces for frogs to get in and out.

5. Add local native water plants. A circulating pond helps control mosquitoes or use tadpole-friendly native fish.