Bosco Verticale and What Tree Towers Really Ask of a Building

Roughly 800 trees, around 5,000 shrubs and many thousands of smaller plants, all growing on balconies up to about 110 metres above a Milan street. When the Bosco Verticale opened in 2014, the photographs did most of the talking. A decade on, the more useful story is what it took to keep those plants alive, and what that means for the dozens of planted towers that have been announced since.

I have walked around the two towers in the Porta Nuova district several times, at different seasons, and the building looks different each visit. That is the point, and also the challenge. A tower that changes with the weather asks far more of its structure, its budget and its maintenance crew than a glass box does. This piece looks at the Bosco Verticale as a project, not a postcard.

What the Bosco Verticale Actually Is

The project, designed by Boeri Studio, is a pair of residential towers, one of about 110 metres and one of about 76 metres. Each apartment has deep, staggered balconies with built-in concrete planters. The staggering matters: it gives trees on one floor room to grow up past the slab above, instead of being boxed in.

The planting was chosen to cover the facades in a way that would match, on a single site, the canopy of a small woodland. Species were picked by height on the building, with hardier plants on the higher, windier floors and more delicate ones lower down.

The Engineering Behind Trees in the Sky

Putting a tree on a balcony is not like putting a pot on a terrace. The structural problems are specific.

Weight

Wet soil is heavy, and a mature tree with its planter can weigh several tonnes. The slabs and cantilevers were designed thicker and stronger than a typical residential tower to carry that load, which also added concrete and cost.

Wind

At 100 metres, wind can tear a tree out of shallow soil. The design team ran wind tunnel tests on sample trees, and the larger trees are restrained with steel cables and safety cages around the root balls so they cannot fall even if a branch or trunk fails.

Water

Each planter is fed by an automated irrigation system, with sensors tracking moisture across the facades. Much of the water reportedly comes from filtered groundwater rather than the mains, which cuts running costs.

Growing the Forest Before the Building

One detail often missed in coverage is the nursery stage. The trees were grown off site for a couple of years before installation, in conditions meant to prepare them for life in planters at height. Root systems were trained to suit the limited soil volume.

That lead time shaped the whole construction schedule. Planting could not be squeezed into the final weeks like a landscaping package on a normal project. It had to be planned alongside the structure, with cranes booked to lift trees into place floor by floor.

How the Towers Change Through the Year

Visit in July and the facades are a solid wall of green, with balconies sitting in deep shade. Visit in January and many branches are bare. That shift is deliberate. A large share of the species are deciduous, so they block hard summer sun and let low winter light reach the living rooms behind them.

For residents, that means cooler balconies in a hot Milan August and brighter interiors in the dark months, without blinds doing all the work. It also means leaf fall. Gutters, drains and balcony outlets need clearing every autumn, and a blocked outlet on the 20th floor is a much bigger job than one at ground level.

The Flying Gardeners

Ongoing care is what makes or breaks a project like this. Pruning and checking the trees is done by a specialist team, nicknamed the flying gardeners, who abseil down the facades from the roof a few times a year. They trim growth, check cables and remove dead branches.

Residents do not prune their own balconies. Maintenance is managed centrally and paid for through service charges, which are high. For anyone thinking of applying the idea on a smaller scale, this is the lesson: plants at height need a maintenance contract from the day of handover, not a hopeful note in the building manual. We saw the same pattern in our look at green roofs on homes and what they really cost, where neglected planting quickly turns into a leak risk.

Where I Push Back on the Hype

The Bosco Verticale is often described as a climate solution. I think that overstates it. The extra concrete and steel needed to carry soil and resist wind carry a real embodied carbon cost, and the trees on two towers will take many years to absorb anything close to it.

It is also a luxury product. Apartments in the towers sell at prices most Milan residents cannot reach, and the service charges reflect the cost of rope-access gardening. Calling it a model for affordable green housing ignores the budget it needed.

What it does do well is real, if narrower. The planting provides shade, cuts noise and dust on the balconies, gives birds and insects habitat in a dense district, and makes a tower feel like part of the neighbourhood rather than a mirror over it. Those are good outcomes. They are just not the same as solving urban emissions.

Lessons for Projects Trying It Next

Planted towers have since been proposed or built from Eindhoven to Nanjing to Sydney, with mixed results. A few cases reportedly struggled after handover, with plants dying back because irrigation or maintenance funding fell short. The projects that hold up tend to share a few traits:

• Planting designed with the structure, not added after the frame is fixed.
• Species chosen by height and orientation, with tough plants on exposed corners.
• A funded maintenance plan covering access, pruning and irrigation for decades.
• Realistic claims about shade, comfort and biodiversity instead of carbon promises.

Similar thinking applies at street level. The High Line and other elevated park projects succeeded partly because a dedicated organisation took on long-term planting care.

FAQ

Can the public visit the Bosco Verticale?

The towers are private residences, so you cannot go inside without an invitation. The facades are easy to see from the surrounding streets and park in Porta Nuova, which is the best way to appreciate the planting.

Do residents look after the trees on their balconies?

No. Care is handled by a professional team for the whole building, including rope-access pruning, so residents do not need gardening skills.

Could a vertical forest work on a smaller building?

Yes, at a smaller scale. Mid-rise blocks can use deep balconies and climbing plants, but the same rules apply: a structure designed for wet soil, automatic watering and a paid maintenance plan.

The Practical Takeaway

The Bosco Verticale shows that trees can live on a tower, but only when weight, wind, water and maintenance are designed in from the first sketch and funded for life. Judge any planted building by its care plan, not its renderings. For more case studies of buildings and the decisions behind them, see our projects archive.