Have you ever noticed how some things emerge, seemingly from nowhere, to capture the zeitgeist, representing for a very brief moment, the very acme of "now"? Last year's craze for all things "pop-up" is a case in point. For a brief period it was difficult to leave the house without being subjected to pop-up cinemas, pop-up restaurants and pop-up boutiques. Even this newspaper ran an issue entitled "Pop-up Abu Dhabi". Such trends normally bubble up from the world of music and youth culture or trickle down from the gallery and catwalk, but not since the 18th century has a similarly contemporary and fashionable impulse emerged from the world of gardening and plants. With vertical gardens, however, that might all be about to change.
Unlike the pop-up, vertical gardens can hardly be described as a flash in the pan. Gardeners have been clothing facades in vines, climbers and creepers ever since the hanging gardens of Babylon. Even in their more contemporary form (where carefully composed combinations of normally ground-based plants are used rather than climbers or vines), vertical gardens have a pedigree that can be measured in decades rather than months; however, the scale and ambition of several recent installations like those created by the French academic and botanist Patrick Blanc have raised their profile and succeeded in introducing them to a wider, more fashionable audience.
Architects Herzog & de Meuron's Caixa Forum contemporary art museum in Madrid, and Jean Nouvel's Quai Branly Museum in Paris, both boast what Blanc describes as murs végétaux. At Branly, Blanc has covered the north facade of the museum's administrative block with an installation that uses more than 15,000 plants from 150 different species to create a vertical garden of almost 1,000 square metres; his wall at the Caixa Forum is equally gargantuan. In creating these, Blanc has not only succeeded in fashioning installations that approach the level of haute couture or fine art, he has also created gardens that are more photographed and famous than the buildings that they clothe.
All of this would be of little more than academic interest if it were not for the fact that prefabricated, off-the-peg "green" or living wall systems are now being manufactured that allow the installation of more modestly sized vertical gardens in the home, office or classroom. Many of these systems come from Canada, the country that has more living walls than any other, and most are used inside buildings, where they are sheltered from the harsh conditions of the North American winter. As well as bringing nature indoors, there are practical reasons for installing large-scale living walls. Externally, they provide food and habitat for wildlife, help to lower urban temperatures, protect building facades, and can even be used to teach children about gardening and growing food. Indoors, living walls can help combat sick-building syndrome and, when connected to fans that pull air up through the blanket of vegetation, can clean, cool and refresh the air, something that's particularly useful in spaces such as atria that are prone to stale, dry air and overheating.
On a recent visit to London I was delighted to see some wonderful vertical gardens in commercial buildings, shopping centres and even in small cafe courtyards. Even more surprising was the one used on a temporary construction hoarding directly opposite Buckingham Palace; it was beautifully planted with a cascading mixture of plants that included helixine (Soleirolia soleirolii), lily turf (Liriope muscari) and alumroot (Heuchera micrantha), all well-suited to the English climate. Though temporary, the garden has been designed to last for at least three years, and like Blanc's work, it shows the dynamic, painterly qualities that can be achieved in vertical gardens by some who understands plants and how they will behave in this most unusual, vertical alignment.
Unfortunately, the same cannot be said for the vast majority of vertical gardens that are starting to appear; smaller examples in particular look set to join the lava lamp in that category of interior decoration designated "novelty".
Often under-planted with spiky, tropical plants that are designed to look contemporary and "edgy", these doormat-sized units have none of the environmental benefits of their larger cousins and all the aesthetic merit of a fibre-optic table decoration.
Even when living walls are big enough and a suitable selection of plants is used, they still offer one of the most unforgiving canvases for planting design - all of those mistakes that can normally be covered up in a horizontal planting bed are exposed for all to see.
So unless you have 1,000 square metres to spare, I'd use my plants to grow up rather than "pop-up" by avoiding the novelty living wall and investing in some naturally climbing and cascading plants instead.