About 10 years ago, when the Hayward Gallery on London's South Bank was under threat of demolition, I ran a competition asking people to think of what we might do to improve the appearance of this seemingly friendless concrete brute. The design that instantly caught my eye was one that transformed the 1960s art gallery by covering it with trailing plants. It would be a kind of Hanging Gardens of London, a place of sweet-smelling flowers, birds and butterflies, for at least a part of the year. Since then, a number of architects and landscape gardeners have taken up the idea of plants roving behind, before, above, between and below city buildings. No one, however, has done it as effectively or eye-catchingly as Edouard François with the "Flower Tower", a 10-storey apartment block in Paris's 17th arrondissement. François has long observed how, given the chance, Parisians will cultivate the tiniest balcony, nurturing surprising greenery in this tightly packed, densely occupied city. He has formalised this hobby in the design of the Flower Tower - so much so that the entire apartment block appears, from the square it fronts and the new streets around it, to be one giant display of potted plants.
