Green Mansions

The title here comes not from any connection to W.H. Hudson’s old book Green Mansions, but rather from its fitting reference to the beauty of rampant green in nature. More than thirty years ago the French botanist and artist Patrick Blanc brought a jungle of sorts into the city of Paris by literally turning gardening on its side and inventing what some people call ‘living walls.’ Blanc’s is a type of urban gardening designed as an art form to decorate city buildings while creating something spectacularly beautiful that also helps enliven a space, humidify the air and moderate indoor and outdoor building temperature. These living walls and green roofs provide relief from excess heat in urban environments due in part to heat absorption from surrounding concrete or asphalt.

The Caixa Forum Museum in Madrid

No doubting the natural beauty of these vertical gardens or the benefits they bring to urban ecology, but the next thought is of what it must do to the structural integrity of a building. Any weekend gardener can tell you that attaching plants to a wall, be it wood, stone or brick will over time damage the wall. Roots open cracks admitting water that can freeze and open fractures, insects follow root tendrils and bring a deterioration of their own. The ivy covered walls on an old church or university are splendid to look at, but the pretty picture has its cost. Patrick Blanc and his followers have solved that problem.

The Musee du Quai Branly in Paris designed and executed by Patrick Blanc

Vertical gardens are attached to the exterior (or interior) of a building so that the plants root in a structural support which is fastened to the wall itself. The frame is built in front of a pre-existing wall and attached at various points. No damage is done to the building. Rigid waterproof panels are mounted to the frame providing structural support. A cushion of air remains between the building and the panels, enabling the building to breathe. This adds beneficial insulating properties which become a rain-screen protecting the building’s original wall. Because the vertical garden is hydroponic (using no soil) it is very clean and eliminates the possibility of soil borne pathogens. A lightweight porous material takes the place of soil making the walls very light. The plants receive water and nutrients from within the vertical support instead of from the ground.

Building in the town square of San Vincente del Raspeig, southeast Spain

Diversity is the key and by utilizing hundreds of different types of plants, striking patterns and unique designs can be created. The gardeners achieve this by utilizing a multitude of colors, textures and sizes. The plants create a garden that filters air and water, soaks up carbon dioxide and helps lessen the “heat island” effect in urban areas, reducing air conditioning costs in the host building.

Unidentified Building in Madrid

While these large vertical gardens are impressive, critics question their sustainability, considering the energy input needed to run pumps and other equipment used to maintain proper nutrient and air flow. Some critics also question the emissions caused by the manufacture and transport of specialized materials. And since larger green walls need more water than rain alone can provide they don’t necessarily save water. Proponents of these large urban vertical gardens assure critics that as the science matures, practitioners are finding wider varieties of plants to choose from, species that are better at taking care of themselves. There is also a move toward scaling back on inputs and supporting machinery with the hope that one day many of the walls will be self-sustaining gardens that cleanse our dirty air as well as impure storm water.