Nowadays, every human activity involves energy consumption. Consequently, it is becoming increasingly important to consider the short and long term effects of our activities on nature.
Today urbanisation is rampant1; nevertheless there are many empty dwellings, and cities are still growing in size. The architectural sector (especially dwellings) is thought to be responsible for up to 33% of the world’s total CO2 emissions2. Cooling down, heating and lighting domestic and working environments involve an enormous expenditure of energy, which is causing serious pollution issues around the world. Therefore, it is clear how important it is to consider energy saving techniques in the design process of developments.
Plants can be involved in this process1 but not just as green playing areas or gardens. In our metropolis vertical surfaces are more numerous than horizontal ones. Why don’t we use these, transforming grey concrete walls into eco-green colourful vertical gardens?
We can distinguish the vertical gardens in two main types: The first type is simpler and based on rampant plants planted at the floor level and directed on the walls as wanted. In the second type plants are installed vertically on the wall, sustained by metal grating, or hung on walls in felt pockets.
The latter idea is commonly thought to be coined by by the French botanist Patrick Blanc, considered as the father of vertical gardens since the 80s3. Patrick Blanc patented his structure of mur végetal in 1988, composed by a metal frame, PVC layer and felt. He merged his architectural and scientific knowledge to create living walls perfectly integrated in the landscape. Blanc’s gardens have an automatic system of watering, in addition to a species specific spatial arrangement in relation to vertical variation of moisture and temperature3. Blanc seemed to be getting his inspiration from rainforest plant organisation, but there is no didactic or ecological intent in his green art. However, his green facades are created to be self-sustainable as possible with minimal energy expenditure.
Here again, sustainability plays a key role. Are vertical gardens sustainable and eco-friendly?
Generally, if not perfectly designed, a green wall needs constant large-scale maintenance, in addition to professional figures (for instance, agronomists or botanists) who are able to monitor the plants’ health. Furthermore, if not well located, plants could be inclined to stand above each other to obtain more sun, at the same time root competition for hydric resources could occur. Stronger plants will slowly kill the weaker or less competitive ones, requiring replacement and further maintenance and extra costs. Furthermore, it is often necessary to use fertilizer to compensate for the lack of biological soil.
However, the number of studies about the positive benefits of green facades implemented in urban designs is increasing4. Vertical gardens seem to have clear insulation capacity, protecting the property’s wall from direct sun light and maintaining warmth during the winter1.The green barriers also provide noise reduction, and extra absorption of pollutants, dusts and fuel emissions3.
So, are they bad or good? It depends, as usual. They are still considered a luxurious extra in an architectural project5. Vertical gardens should have a strictly defined design, in order to maintain plants and their benefits without extra costs. They should promote biodiversity and recreate local environments, in order to be used as green spots in cities for wildlife (eg. birds and insects). Furthermore, they should be created in accordance with the local weather and environment in order to further reduce the maintenance costs.
Essentially, we are still working on it. There is a lot of potential in the wide field of urban botany, and there are many more applications yet to be discovered for it.