Sometimes nature is the best teacher
Skyscrapers draped in greenery, roof gardens and planted facades provide shade, store moisture and absorb toxins from the air – architects and city planners are tapping the power of luxuriant greenery to boost the quality of life in urban centers.
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Throughout the year, green and colorful flowering climbers wrap their way around the 117-meter-high facade of the urban oasis that opened in 2014. The project required much more planning and expertise than balcony gardeners can imagine. “Designing a vertical garden is a combination of science and aesthetics,” says French botanist Patrick Blanc, who is considered the modern innovator of the vertical garden. Together with Parisian architect Jean Nouvel, Blanc designed One Central Park, and selected hundreds of suitable plant species, roughly half of which are endemic and therefore unique to Australia.
“The right plant in the right place,” says Blanc, summarizing his botanic concept. Robust grasses and shrubs are more suited to the upper floors exposed to wind and sun. They also provide shade, thereby reducing the strain on power-hungry air conditioning systems. Middle floors afford the plants more protection and serve as a habitat for vines and more sensitive flowering plants. Ferns, rhododendrons and azalea species do best on the lower floors where there is less sunlight.
The ability of planted walls to purify the air has been demonstrated“
Blanc seeks inspiration for his work on numerous expeditions into the plant kingdom. He chooses plants according to his motto: from nature to the city! To this end, his high-rise habitats often feature species that can survive outdoors on cliffs or trees without a conventional plant base of soil. “Soil merely acts as a mechanical foundation anyway,” says Blanc.
Plants only need water, minerals, light and carbon dioxide for growth and photosynthesis. Be it in Tokyo or Paris, Riyadh, São Paulo or New York - Blanc largely does without fertile soil in his more than 300 vertical garden projects. An ingenious system of little hoses supplies water and nutrients automatically to each plant, which puts down roots on a substrate made of basalt or mineral fiber. As well as using this low-maintenance hydroponic system, the plants even fertilize themselves from the city air - a welcome side-effect of the process of filtering particulates and nitrogen oxides that pollute the air in cities.
Bringing more greenery into urban areas is also one of the strategies for making cities more livable, as endorsed by the international community in 2016 at the UN Conference “Habitat III” in Quito, Ecuador. In addition to improving air quality, this can also allow more greenhouse gases to be absorbed and broken down - an urgent priority since urban areas cause more than 70 percent of carbon dioxide emissions. “The ability of planted walls to purify the air has been demonstrated,” says Rob MacKenzie of the School of Geography, Earth and Environmental Sciences at the University of Birmingham. The chemist has already shown in a much-quoted 2012 study that planted facades can reduce the concentration of particulates and toxic nitrogen dioxide by as much as 90 percent.
So it is hardly surprising that Patrick Blanc is not the only one to extol the numerous benefits of strategically planted structures. The Bosco Verticale, a vertical forest planned by Italian architect Stefano Boeri, was constructed in Milan almost in parallel with the One Central Park Sydney. For this project, he designed two residential buildings - 116 and 85 meters high respectively - with expansive balconies on all sides. Covering an accumulated area of 20,000 square meters, they provide space for a total of 700 trees and 5,000 shrubs, securely planted in concrete tubs that are just under one-and-a-half meters deep. Thousands of creepers and flowering shrubs round out the planting of this magnificent green building. In collaboration with botanists from the University of Milan, Boeri sought out twenty different species of deciduous and evergreen trees as well as eighty additional plant species for the plant cover on the facade. The result? The Bosco Verticale changes its appearance with the seasons and never appears bare.
“The vertical forest creates its own microclimate and increases the air humidity,” explains Boeri. Each year, his trees and bushes absorb 20 tons of the greenhouse gas carbon dioxide and release almost the same amount of oxygen back into the city’s air. Dust particles and nitrogen oxides from exhaust gases are also efficiently absorbed by the plants. As well as improving the air quality in the immediate vicinity of the building, the project benefits urban biodiversity. From larks to sparrows, more than 20 species of bird nest in the biotope. A microclimate forms around the building, reducing the air temperature by up to two degrees, particularly during the summer months. In this way, the Bosco Verticale effectively counters the heat island effect that drives summer temperatures in densely built-up urban areas several degrees higher than the surrounding countryside. “Essentially, this is a tower for trees,” explains Boeri, “which is then also inhabited by people.”
The city of the future can only be a green city.“
“The city of the future can only be a green city,” acknowledges Alexandra Quint, urban theorist and expert on sustainable urban development at Karlsruhe Institute of Technology in Germany. She even advocates the use of crop varieties for cooling building facades, fruit and vegetables on balconies and freely accessible bodies of water. With their new building projects ranging from residential towers all the way to the planned city, Stefano Boeri and Patrick Blanc are already getting quite close to these ideals. Yet fully developed cities, too, must not overlook the need to add greenery for a better quality of life.
CityTrees and urban gardening
“In the future, there will be planted areas that we have not yet considered,” predicts Christian Ulrichs, who heads up the Division of Urban Plant Ecophysiology at the Humboldt University of Berlin. He recommends adding plants to urban furniture such as bus stops or advertising columns. Were city dwellers also to become actively involved in this planting movement, better air quality and high levels of biodiversity of flora and fauna could be achieved even more quickly than with the help of ingenious new buildings and smart inventions. For instance, the number of roof gardens in cities around the world is increasing with the support of non-profit organizations such as Green Roofs for Healthy Cities in the U.S. Many city administrations and nature conservation associations offer concepts for sustainable and, above all, insect-friendly balcony planting. These concepts can be used to generate a level of biodiversity that rural communities surrounded by vast fields of rapeseed or corn can only dream about.
Urban gardening - the cultivation of vegetables and herbs in private or communal spaces - has also long ceased to be considered an eccentric pastime of a few enthusiasts, and is becoming a hip trend with a growing following, particularly in sprawling cities. Even the allotment garden - previously regarded as the epitome of bourgeois living - is shedding its stuffy image.