This planted wall on a Tokyo boulevard elevates a simple site hoarding into an extraordinary living work of art intended to engage with and stimulate the senses.

By definition, building site hoardings are rarely things of beauty. But here on Tokyo's Omotesando Avenue, the humble hoarding is transformed into a living, growing, green entity. Behind the 274m-long fence a huge mixed development by Tadao Ando is slowly taking shape, but construction work will take three years. In the meantime, shoppers, strollers and office workers are distracted and charmed by an evolving curtain of foliage, a rare flash of greenery in a city with few parks and limited public open space. Conceived by architectural funsters Klein Dytham, it follows on from the practice's earlier site hoarding experiments, most memorably a shimmering inflatable wall made of silver balloon fabric (AR June 2000). Here the theme of planting is energetically explored, taking its cue from the ivy-clad apartment block that used to occupy the site and the tree-lined boulevard of Omotesando, Tokyo's Champs Elysees. The client's name, Mori, also means forest in Japanese.

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Klein Dytham needed something that would improve over time and react to changing seasons, but an all-planted hoarding would have been prohibitively expensive. Instead they designed a bar code style pattern of alternating strips of foliage and panels of graphic greenery. Over time, the planting will grow and fill out to cover the hoarding. Thirteen different types of evergreens were selected, including ivy and blue grass, and aromatics such as mint and rosemary. The main challenge was to find a simple way to irrigate the planting without resorting to spraying from the front, which the Tokyo authorities would not permit. So, instead, plants are contained in felt cups that make contact with a thin felt backing panel. Water is dribbled in from the top of each panel to moisten the backing felt and then seeps through to the felt cups, keeping the plant roots moist. The organic part of the fence also needed to be fairly lightweight, as earth panels would have required a very heavy, and expensive, support system.

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In its busy urban context, the scale and relationship of alternating plants and graphics works well for pedestrians at walking speed. People, especially children, are fascinated by it, touching and stroking the grass and plants. In the heat of the summer, the green hoarding is an especially welcome sensuous, cooling presence that animates and enriches everyday city life.