Height, floor space, and the number of units are the usual key figures in investor-financed high-rise construction. But 800 trees, 4,500 shrubs, and 15,000 other plants are the key figures Stefano Boeri cites for his Bosco Verticale (vertical forest) in Porta Garibaldi, Milan. With the two green residential towers, 110 and 76 m high, the Italian architect and his team...