Chelsea Flower Show: garden designers in balancing act

One of the great challenges for show garden designers at Chelsea Flower Show is to tread the line between producing a garden that withstands the scrutiny of the judges, the public and the television cameras while, at the same time, delivering the sponsor’s message.

When there is no message to promote, the designer can revel in the freedom of making a garden that simply (and loosely) reflects the sponsor’s aspirations. But when a backer gets a little too enthusiastically involved, the results can be disastrous. A few years ago one sponsor insisted that its garden should drip from top to tail with its corporate colour scheme. The result – a garden in which the planting, hard landscaping and even the garden building were colour-themed – undermined the design, which fared poorly in the contest for medals, picking up only a bronze.

On other occasions, the best efforts to promote a specific message are undone by happenstance. The Royal Society for the Protection of Birds exhibited a wildlife garden specifically designed to attract birds, complete with habitats, feeders and fruit- and nut-bearing trees. As the show ended and the gardens were dismantled, a pair of nesting blackbirds with a brood of chicks was discovered in a hedge, resulting in it being left in situ until the chicks fledged. The whole affair attracted considerable media attention but, with horrible inevitability, the hedge was not in the RSPB garden at all but the one next door.

For the 2013 centenary Chelsea Flower Show, the Royal Bank of Canada, Professor Nigel Dunnett and The Landscape Agency (TLA) are embarking on a third successive garden together, the previous two having been awarded silver-gilt medals. RBC has had a strong message to promote through its previous two gardens, and it is the same this year. Since 2007, the bank has pledged, through its Blue Water Project, more than C$33m (£21m) to about 450 not-for-profit organisations that provide access to water that is drinkable and where you can swim and fish. I saw one of these schemes a couple of years ago near Hamilton, Ontario. In a lake infested with invasive non-native carp – which were eating anything and destroying the fragile lake ecosystem – Blue Water funds had been used to implement an ingenious “fish lift” system, enabling native and non-native fish to be separated out, so the non-natives could be eliminated.

RBC has used Chelsea as a platform to promote the Blue Water project and to highlight innovative water management technology in gardens, an area in which Prof Dunnett specialises. Dunnett, professor of planting design and vegetation technology at Sheffield university, was one of the consultants involved in the planting design at the Olympic Park last year. TLA, a landscape architecture practice, has collaborated with Dunnett for several years, most recently on the first London street-side rain garden, planned for retailer John Lewis’s London head office. The two previous RBC Chelsea gardens explored water saving and water management techniques, ecological ideas and environmental principles, while trying to balance those heavyweight themes with attractive planting and landscape design. While it is not as invidious as having to design a planting palette in corporate colours, it is a challenge nonetheless.

The 2013 garden is designed as an urban rooftop, complete with air conditioning units, cooling vents and ducts. In one corner is an interactive garden building, described as a contemporary bird hide, featuring the kind of one-way glass used in criminal identity parades. The idea is to enable wildlife to be watched without the need for the watcher to stay still. The building has a green roof and habitat panels (which encourage beneficial insects to breed), with nest boxes for house sparrows, once a common species in the UK but now in decline.

Habitat panels to promote biodiversity

The design demonstrates rain garden techniques, an area that has been gaining profile for some time in the US but is still under the radar in the UK. The basic principles are simple: every drop of rain that falls on the garden and the structures within it is captured and either recycled or, through use of permeable materials and planting, allowed to percolate slowly and evaporate, or be taken up by living plants. The benefits of this are obvious: urban drainage systems are often at or near capacity, unable to take the increased inputs that come with development. In London, for example, a rise in on-street parking charges and restrictions has led to more front gardens being paved over to accommodate off-street parking. It is not solely an issue in the capital. About one-third of the 21m homes in the UK with a front garden have been turned into paved parking spaces in the past 20 years. That is 14,200 hectares of green space, equivalent to two-and-a-half Manhattans, that would have allowed storm water to dissipate rather than head for the nearest drain.

As well as storm water run-off, Dunnett and TLA have included open water rooftop wetland as a means of cleaning and purifying grey water for domestic use. Using recycled grey water for garden irrigation is not new, and the thinking behind it – that the use of drinking water for garden irrigation is ultimately unsustainable – is well established.

What the RBC garden sets out to demonstrate is that a rooftop is an ideal place to locate the reed bed and wetland system needed to clean the grey water, before use for irrigation or toilet flushing. This is planted with architectural water plants such as the barred horsetail, Equisetum ramosissimum var japonicum and Phragmites variegatus, the variegated Norfolk reed. The use of Cyperus eragrostis, the pale galingale, demonstrates the minefield facing any design where ecological principles are promoted. It is a striking and elegant native of the western US but also one that has become an invasive pest in many countries where it has been introduced. That is the trouble with plants; they can be a godsend in one continent and a hound of hell in another. Next to the reed bed is a wetland marginal planting, with desirable specimens including a mass of blue Meconopsis, a plant coveted by many and not at all easy to grow. In a rooftop garden, it should be free from the slugs that love to chew it at ground level but would it cope with the exposure?

The concept of “sky-rise greening” is gaining ground in many urban environments as land values in prime locations drive architecture increasingly upward, and the design bears that in mind, integrating habitat features with recreational living space. Plants with exposure- and drought-tolerance feature heavily in the open, sunny part of the roof garden. Dianthus carthusianorum, a species pink with vibrant cerise flowers, was a star of the show in 2011 and is used here with the greenish yellow species grass Festuca amethystina and tiny-flowered Gypsophila repens “Rosea”. The result should be colourful and airy, and require the minimum amount of irrigation.

A low-tech living wall using drought-tolerant plants placed in land drains

The garden also takes a critical look at living walls, which have gone from experimental and often unreliable technology to ubiquity, with prominent examples in public landscapes as well as domestic designs. Dunnett and TLA argue that the volume of water required to keep high-tech living walls thriving renders them unsustainable. Instead, they have reverted to low-tech living walls, using drought-tolerant plants such as Sempervirens and Sedum, planted into recycled terracotta land drains and stacked roof tiles packed with the gritty, fast draining soil they thrive in.

This is a garden that poses plenty of questions via the use of new techniques and technologies. Whether the team has managed once more to tread the line between those messages and the overall cohesion and attractiveness of the design will be clear when the 100th Chelsea Flower Show opens.

Matthew Wilson is managing director of Clifton Nurseries in London

The Chelsea Flower show runs from Tuesday May 21 to Saturday May 25, 8am to 8pm. Tickets numbers are capped,

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