London is a city of parks and trees. It has just acquired another burst of greenery in the shape of a vertical garden climbing up the Athenaeum Hotel on Piccadilly. As the Athenaeum is opposite Green Park, there is a rightness to it.

Like most of London’s 1970s architecture, the hotel, designed as offices, is the kind of building that almost anything, including demolition, would improve. But the vertical garden goes further; not only is it spectacular in itself, but it introduces a new idea. As cities become denser, space for gardening is at a premium. Why not use walls?

It took a Frenchman, Patrick Blanc, to come up with the concept. With his green hair and floral shirt, he looks rather like a vertical garden himself. Not merely a designer, however, he is also a botanist, who personally hunted for some of the plants used in London. The theory is that a wall garden is like the rainforest, its vegetation changing from canopy to dense shade as it descends the building.

Each plant is grown in a pocket of what looks like felt, and has, indeed, been made from recycled clothes. I’m assured that it won’t degrade; the nature of a vertical garden is that maintenance is limited. To some home gardeners, that may be another plus. My suspicion is that we’ll all be doing it soon.