Are Architects Going Overboard With the Trees on Buildings?

Bosco Verticale
©. Stefano Boeri

© Stefano Boeri

It's the rendering that launched a thousand blog posts, Stefano Boeri's Vertical Forest, with planters and trees on balconies and the roof, so green that you can barely see the building. Tim De Chant notes that it is just one of many that architects are drawing these days.

Want to make a skyscraper look trendy and sustainable? Put a tree on it. Or better yet, dozens. Many high-concept skyscraper proposals are festooned with trees. On the rooftop, on terraces, in nooks and crannies, on absurdly large balconies. Basically anywhere horizontal and high off the ground. Now, I should be saying architects are drawing dozens, because I have yet to see one of these “green” skyscrapers in real life.
Besides knowing a lot about urban design, Tim evidently knows something about trees, and wonders if they belong at such heights.
There are plenty of scientific reasons why skyscrapers don’t—and probably won’t—have trees, at least not to the heights which many architects propose. Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It’s hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity. Life for city trees is hard enough on the ground. I can’t imagine what it’s like at 500 feet, where nearly every climate variable is more extreme than at street level.

© Stefano Boeri

Tim doesn't mention what I think is a bigger problem: the size of the planter. City trees have enough trouble finding enough space for their roots at ground level in sidewalk planters, and even if they survive, they rarely grow much bigger than they were when they were planted. The American Standard for Nursery Stock suggests that a 36" planter can hold a tree with a maximum caliper of 3.5 inches. So are the trees on this building ever going to look like they do in that rendering?

Milano Santamonica

Studio Nicoletti/Promo image

Sometimes they are just unrealistic and impossible, even as renderings. As I noted about this dead project at the time,

One really cannot tell if there are planters in front of the handrails or if it is just sorta stuck there like Christmas decorations. Nor do you know who maintains them, whether each owner is responsible, whether gardeners have rights of entry, or whether they rappel down the exterior of the building.
Flower tower

© Paris Invisible

Édouard François tried this back in 2004 with his Flower Tower, putting bamboo in large planters. Visiting it in 2011, Invisible Paris found that the "The bamboo is not in perfect condition, but certainly in a better state than could have been expected". It has grown out to look quite different from when it was first planted, and it appears that some of it is struggling. And this is bamboo, not big trees.

De Chant concludes that it is all futile.

Trees just weren’t made for such conditions. Now if someone want to gin up a tree that can survive on top of a skyscraper, go ahead, I guess. But I can think of far better things we should be putting our time and effort into, like preserving places that already have trees growing on them or planting more on streets that need them.

I conclude that it is all greenwrapping:

Architects use all kinds of tricks to make their buildings look better in renderings; mirrored glass used to be a favourite, with renderings of buildings showing reflections of sky and clouds as the building just blended into the landscape. As we have noted before, green roofs are the new mirrored glass, as architects bring roofs down to ground level and blur the line between landscape and building.

Perhaps a landscape architect should have to approve the perspectives, declaring that yes, the building will look like the rendering in five years. Otherwise we are probably going to be seeing a lot of really scrawny or dead trees on our buildings.