The medal-winning RBC Blue Water Roof Garden: rainwater for a living roof

A gold medal-winning garden at this year's Chelsea Flower Show makes full use of our greatest natural asset - rain.
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Here is the blueprint for turning London’s skyline green: a roof garden that combines a beautiful living space with innovative biodiversity, bringing trees, meadows and wetlands into the heart of the city. Not surprisingly, it bagged a gold medal at last week’s Chelsea Flower Show.

Roof-top gardens
© Photograps by Marianne Majerus
A bird hide with wildlife habitats on the walls can double as a high-rise workspace

It’s a modern take on the famous roof gardens of Kensington High Street first laid out in the Thirties, says designer Professor Nigel Dunnett, lead horticultural and planting design consultant for the London 2012 Olympic park, together with The Landscape Agency.

Roof-top gardens
A living wall and wetland plants collect every drop of rain
“The Kensington gardens have always had different areas such as woodland and a flamingo lake — but I’ve taken that idea and used it in an environmentally positive way,” he explains.

“With limited space at street level, we need to look skywards to find the green spaces that will allow people in cities to maximise their contact with nature. We’ve created a ‘living roof’ that is able to collect and filter rainwater, allowing plants to flourish on top of skyrise buildings all year round.”

The central wetland area of his medal-winning RBC Blue Water Roof Garden comprises moisture-loving plants that take up rainwater so that it doesn’t simply run away into drains. This makes a grand excuse to grow irises, rushes and equisetum grass in islands of concrete drainpipe slices, within a pebble pond, that has, depending on the elements, a variable water table.

Taste of the high life
A winding boardwalk of sweet chestnut leads to a dynamic contemporary building that Dunnett says is a bird hide — but there’s nothing to stop the city dweller from settling in with a laptop instead of binoculars. There is, of course, a green roof to absorb water on top of the structure — Dunnett is the pioneer of eco-friendly green roofs — that, as well as cerise-flowered trailing ice plant Delosperma cooperi, has piles of logs and small stones as refuge for insects and butterflies.

There are further opportunities for wildlife in high-style habitats on the bird hide’s walls that could pass as rather fabulous modern sculptures. “I don’t see why bug hotels shouldn’t look as beautiful as anything else you might have in a garden,” says Dunnett.

Roof-top gardens
Alpine gentians grow beneath the grille walkways
Instead of the usual fencing or trellis to separate the space from the neighbouring rooftop, Dunnett created a low-irrigation living wall. Usually, living walls need complex and costly irrigation systems to thrive, but this one has individual terracotta planting units made from slices of agricultural field drains, cleverly angled so they catch rainwater. And should there be a period of drought, the plants selected — sedums, thymes and succulents — can survive without water for long periods.

Whereas planting in a roof garden is often formal or minimalist, Dunnett’s is naturalistic, so that in a hot, dry area, from which rainwater drains away, a mini-prairie of purple Verbascum phoeniceum Violetta thrives; at the front of the garden, a luscious glade of ferns and Himalayan blue poppies flourishes beneath a white-flowered dogwood, Cornus kousa chinensis. And, beneath the pathways of metal grilles designed for visitors to make minimal impact to wildlife, grow glorious cobalt-blue gentians: a heavenly touch, fitting to this exceptional garden in the sky.

The RBC Blue Water Roof Garden echoes the work of the 10-year RBC Blue Water Project, helping protect the world’s fresh water resources. Visit for more details.

Pictures by Marianne Majerus

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