For Barcelona area landscape designer Marc Grañén, the test of his concept was the reaction from his young children. When he told his kids, ages 6 and 9, about his lightweight green roof system for city buses, the boys began drawing pictures, telling their friends, and offering up wildly imaginative suggestions. “They go crazy when they talk about it,” Grañén said about his children’s response.

Grañén’s young son Arnau explores the bus’s rooftop garden.

With his project, PhytoKinetic, Grañén aims to energize drab public buses with vibrant, gardened roofs that he hopes will contribute a bit to improving the urban ecosystem. “Urban green areas are crucial for photosynthesis, vital for purifying the air we breathe,” he said. “But much-needed green areas are not always available.”


Grañén believes cities can use existing spaces–like the roofs of public buses–to create new pockets of greenery. A self-described “landscape artist,” based about an hour north of Barcelona, in Bescanó, Grañén first studied biology before turning to one of his passions, garden design. ”My artistic point of view of life and my intense love of natural landscapes make the perfect combination for what has become my daily occupation. I am a landscape artist, says Grañén. “Nature is my inspiration and my family, my best teacher.”

Grañén planting the PhytoKinetic prototype.

Grañén‘s children offered their input.

When he met the lauded green wall and green roof innovator Alex Puig at a garden event in which they both participated, Grañén was drawn to Puig’s profound yet simple philosophy about greening urban areas in accordance with natural models. Puig’s commitment to biodiversity and multiculturalism resonated for Grañén, who recognized a kindred spirit.


Grañén brought his PhytoKinetic concept to Puig, proposing a mutually agreeable scenario: in exchange for the use of Puig’s Vivers Ter nursery facilities and equipment for PhytoKintetic experimentation and prototyping, Grañén would commit to utilizing Puig’s plants and labor for future projects.

Alex Puig’s Vivers Ter nursery in Girona Spain.

It was the beginning of what Grañén describes as a symbiotic relationship between the two–Grañén bringing the idea and Puig contributing the material and intellectual support in which to implement it. So it comes as no surprise that PhytoKinetic is more than just a magic bus for the 21st century: it’s a practical yet inspiring vision for a greener world.

Urban Gardens Views PhytoKinetic Prototype Bus

Grañén introduces me in June 2013 to the Phyto Kinetic prototype bus near Girona, Spain.

I met Grañén recently when he invited me to Girona to see his prototype PhytoKinetic bus, five months after he reached out to me about it via this blog. We climbed a ladder to the bus’s planted roof, where I was able to experience first hand the living mobile garden that I’d learned so much about since we began communicating in January 2013.



The bus is on the road these days transporting tourists to and from a nature and camping facility in Estartit near Girona. But Grañén is in discussions with a major auto company who has expressed interest in sponsoring a fleet in Barcelona.

In the meantime, Grañén’s received approval to plant the vehicle roofs of a Barcelona landscape design company and another in Girona which he’ll be unveiling in a few days. In September, Grañén will take one of those vans on the road to the World Green Infrastructure Congress, an international event in Nantes, France about developing green infrastructures.


Scientific Community Offers Their Support
An impressive cadre of scientists and engineers have consulted with Grañén in support of PhytoKinetic. The collaborative team has included mechanical engineer Xavier Castellano, a former classmate who works for a major automotive company, who conducted numerous structural tests. Jordi Sargatal, a recognized naturalist, ornithologist and former director of the Fundació Territori i Paisatge, a conservation and environmental education foundation, has advised Grañén about biodiversity. Enrique Figueroa, who teaches ecology at the University of Seville, assisted Grañén in analyzing Co2 capture rates, as did Dr. José Mª Durán and Dr. Julián Briz, agronomic engineers at the Technical University of Madrid and members of Pronatur, a Spanish non-profit that supports green roofs and urban agriculture.


“All these people have worked with me gratis because they trust and believe in the project,” said Grañén.


Up to Scrutiny
Still, the notion of putting plants atop a moving vehicle raises questions. Will the added weight reduce gas mileage? Will maintaining the plants require excessive water use? What will happen to the plants if the bus is in an accident? A similar project, Bus Roots, developed by NYU graduate student Marco Antonio Castro Cosio which we covered two years ago, drew skepticism for not fully addressing such practical concerns. And although Cosio has produced two Bus Roots prototypes, his project remains more conceptual, while Grañén ’s well-researched design is ready for wider implementation.

How PhytoKinetic Works


Plants and Weight
Grañén utilizes a lightweight, 7-centimeter thick hydroponic foam which is much lighter than soil, thereby significantly reducing the overall weight of the PhytoKinetic roof. The foam retains humidity and is extremely flexible, making it easy to install regardless of the shape of the bus roof.



Variously hued sedum plants carpet the surface to add color, changing with the seasons, and absorbing sunlight to protect the hydroponic substrate and regulate the rooftop’s temperature. Small shrubs add visual interest. Grañén foresees each city bus line cultivating its own unique landscape of aromatic herbs, ornamental plants, ivy or grasses. “These types of plants can be found everywhere in the world, but it is important to consider each city’s weather in determining which varieties to use,” Grañén said.


Water and Waterproofing
A perforated stainless steel grid keeps water moving to prevent stagnation. The design employs a polyuria waterproofing system, AquaPro, which dries in ten seconds and permanently seals the roof to prevent leaks.


PhytoKinetic’s closed perimeter boundary design is flexible and adaptable to any roof shape and does not interfere with emergency exits, antennas and other mechanical elements such as air conditioning, filters, etc. that may be located on the roof.



Condensation from the bus’s air conditioning system, which is typically wasted, is captured and recycled to irrigate the roof. The hotter it gets, the more water the plants need and receive. In cooler weather, when the air conditioner is not in use, the garden can be manually watered or buses can drive through special car washes capable of withholding soap and without the overhead mechanical brushes that could damage the garden.


Micro-perforated stainless steel bands fixed in place with ultra-light protective mesh anchor the planted surface should an accident or sudden braking occur. Grañén said he has tested the mesh with a mechanical engineer, finding that the material holds plants in place even in the event of an accident causing the bus to flip over.


Energy Savings
When tested in the heat of summer, a PhytoKinetic bus was 3.5ºC cooler than a regular bus. “Madrid, for example, has more than 2.500 buses. Imagine how many more are on the streets of New York City streets.” says Grañén . Calculating that the average bus roof size is 20 square meters, Grañén figures this amount to approximate more than 100,000 square meters of green roof in New York City.


All practical aspects aside, Grañén believes that his buses have the power to change our relationship with the earth– to integrate urban and natural spaces. Instead of feeling separate from nature, he says, urbanites can feel closer to living, breathing plants. The notion of buses as dirty, fuel-guzzling contaminants would change: Just seeing plants hanging from a bus roof, or arriving at work in a moving garden, hopes Grañén, would begin to alter preconceptions and generate more public interest in greening our concrete jungles. “People have to think beyond these prototypes,” says Grañén . “They have to imagine a city with more green walls, roofs, buses, public buildings, even in the interiors of buildings.” Grañén is not alone in his point of view.


Jaume Terradas Serra, Professor Emeritus of Ecology at the Universitat Autònoma de Barcelona, has endorsed PhytoKintetic, commenting that he believes “this idea is interesting and worth considering: the techniques for creating green roofs and vertical gardens in cities exist. They must be publicized so that people are able to see that they are viable. If the project is successful, it will represent a new economic activity within the framework of greater integration of urban and natural systems. When applied as standard practice, it can help contribute to improved sustainability in cities.”

Julian Briz, Founder/President of Pronatur, believes Granen’s project can steer people beyond the obvious, encouraging them to think outside the box for other innovative green solutions.

“As we continue to solve traditional environmental problems with technologies like green roofs and green walls,” explains Briz, “these innovative solutions can lead us to new methods, opportunities, and places for greening our world–including the roofs of urban buses, trucks and vans, trains and trams, and even ships.”


Looking forward, Grañén imagines offering branded PhytoKinetic green roofs with sponsor logos created from plants. Advertising on buses and other vehicles is not new, but this application would not obstruct riders’ views, while have an environmental benefit while x and could help subsidize city transportation costs. He figures with the efficient production of several buses planted at once, the cost of this “greenvertising” could be greatly reduced.

Grañén’s numerous brand collaborator logos on display. Photo: Robin Plaskoff Horton, Urban Gardens

For now, Grañén sees himself as a sort of green pioneer. As for critics and skeptics, he has no problem conceding that his project is not perfect, but a starting point for better and better versions.  “Mistakes offer opportunities for solutions,” explains Grañén. “Edison performed a thousand failed experiments before developing the light bulb. And today, our critics use them everyday.” The point, believes Grañén, is to keep trying, to keep imagining a better, greener world.


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