Trees take root in unlikely places, wherever a seed lands in a pocket of soil with a supply of water.  A rowan tree lodged in a crack halfway up a cliff face or a buddleia in the chimney of a derelict building may not thrive but it hangs on to life and grows to the limit of the resources available to it.  Trees planted by humans in unlikely places often don’t do so well.  Grown lush in the ideal conditions of a tree nursery then transplanted to a container on a windswept balcony a tree may be stunted by lack of water and nutrients, vulnerable to pests and diseases and unstable due to lack of proper anchoring.  Four years after the inauguration of Milan’s Bosco Verticale (or vertical forest) the 700 trees planted on the two tower blocks seem to be thriving against the odds.  Their survival wasn’t left to chance.


I’m wary of artists’ impressions of futuristic buildings covered in vaguely rendered vegetation. It’s too easy for an architect to add an optimistic green haze to a computer generated image and much more difficult to ensure that real plants can grow and thrive in an artificial environment where they are dependant on human intervention for all their needs.

Trees were integral to Stefano Boeri’s design for the Bosco Verticale rather than an ecologically minded afterthought.  The choice of species and their placement was planned by botanists and horticulturalists over three years, taking into account the aspect and microclimate of different parts of the buildings and the specific requirements of each plant species.  A number of different systems for anchoring the trees were devised, adapted to different locations. The trees themselves were accustomed to appropriate conditions while still in the nursery. Irrigation systems, using recycled grey water, were built in to the water management of the buildings.  A telescopic crane mounted on the roof of each building allows abseiling arborists and gardeners to make regular maintenance visits to all the balconies without disturbing the human residents.  Impeccable planning paid off.  The trees, shrubs and herbaceous plants are thriving, birds are nesting, the innovative buildings have received international acclaim and Boeri Studios now have projects in the pipeline for vertical forests in Germany and China.

The vegetation of the Bosco Verticale is said to be equivalent to a hectare of forest land.  The trees cool the buildings, filter the air reaching the apartments and support varied wildlife.  As part of the regeneration of an inner city area the buildings are a wonderful innovation and yet I still can’t like them unreservedly.  I think my reservations come from the niggling concern that a high tech, human-dependent vertical forest might come to be seen as equal to a natural forest.  If we can recreate a forest on a tower block, conveniently situated next to a major railway station, why bother about conserving the last remnants of ancient woodland on a city’s outer fringe?

The architect who dreamt up the vertical forest must have considered similar reservations. In a summary of lessons learned from the first Bosco Verticale Stefano Boeri makes it clear that his concept is intended to be an ‘anti-sprawl’ devise, offering inner city dwellers the green views previously only available in leafy suburbs.   Here’s his manifesto.