One Central Park: what we ask of a green wall

Near the top of the taller of One Central Park’s two towers, in Sydney, a cantilever houses a motorised heliostat, a set of mirrors that sends sunlight down into the neighbouring park. Below it, twenty-three green walls, 1,200 m² in all, clothe the façades. Jean Nouvel designed the scheme, completed in 2014 in the Chippendale district, with the botanist Patrick Blanc. In his walls, plants grow on felt, without soil. Climbers trained on steel cables add to them, so that greenery covers about half of the façades.

The choice of plants is the most remarkable thing about the project: 350 species, 250 of them native to Australia, according to the Australian research centre for water sensitive cities. Irrigation comes from a plant in the basement that treats the building’s wastewater. The walls live on water the residents have already used.

Nowhere did we find what these walls were meant to do, written down before planting and checked since. Yet this takes neither a laboratory nor a large budget, and any client can do it. A school planting its playground can set out in its brief what it expects: shade at break time, a few degrees less in the classrooms in June, blue tits in spring. A summer or two later, a thermometer and a notebook are enough to know whether it worked. For a house, one sentence will do: what the hedge should shelter, what the vine should shade. Without a written aim, planting is judged only on its photograph.

For One Central Park, three answers are missing. How many degrees do the walls take off the flats they shade? How many plants have had to be replaced since completion? Which birds and insects live there? The answers may exist with the building’s managers. Published, they would let other clients make use of them.