NOW THAT WE'VE FIRMLY established the importance of green roofs... what about green walls? There's no reason that plants have to be relegated to horizontal surfaces -- that's inflexible human thinking. Vegetation can't get up and walk around, but it can sure climb... the tallest tree that's still standing on Earth reaches over 112 metres -- five stories higher than the Statue of Liberty! To dispel our preconceptions about the possibilities for plant life on the Y-axis, let's begin this trilogy of blogs about bio-walls with the work and words of the world's best designer / builder of "vegitecture", Patrick Blanc:
IN THE WILD, plants grow on vertical surfaces. Whenever water is available all year long, as in tropical forests or in temperate mountain forests, plants can grow on rocks, tree trunks and soil-less slopes. In Malaysia, for instance, out of the 8,000 known species, about 2,500 are growing without any soil. Even in temperate parts of the world, many plants are growing on cliffs, cave entrances, or fallen rocks. Many Berberis, Spirea and Cotoneaster species grow in such very steep places. Their naturally curved branches indicate that they originate from naturally steep biotopes and not from flat areas like the gardens where people usually grow them. Thus, as seen from nature, it is possible for plants to grow on nearly soil-less vertical surfaces as long as there is no permanent water shortage.
WHENEVER ROOTS ARE ALLOWED to grow deep inside a wall, they can easily damage the wall and cause its destruction. That is precisely what happened to the Angkor temples. This root-related damage can be prevented if water is regularly given to plants. Roots are then only spreading on the surface, leaving the inner wall unaffected. From these observations, and aiming at setting up permanent plant cover on walls with a minimum of maintenance, Patrick Blanc conceived the Vertical Garden.
THE CORE INNOVATION is to use the root ability to grow not only in a volume (of soil, of water, of sand, etc.), but also on a surface. Without any soil, the plant-supporting system is very light and thus can be implmented on any wall, whatever its size. The Vertical Garden can also be set up indoors. Artificial lighting is then usually required. It's even possible to set it up in fully closed places without any natural light such as underground parking lots. The plant species selection is mainly set according to the prevailing climactic conditions.
THE VERTICAL GARDEN is composed of 3 parts: a metal frame, a PVC layer, and a layer of felt. The metal frame is hung on a wall or can be self-standing. It provides an air layer acting as a very efficient thermic and phoric isolation system. A 1 cm -thickPVC sheet is riveted to the metal frame. This later brings rigidity to the whole structure and makes it waterproof. A felt layer, made of polyamide, is stapled on the PVC. This felt is rot-proof and its high capillarity allow a homogeneous water distribution. The roots grow on this felt.
PLANTS ARE INSTALLED on this felt layer as seeds, cuttings, or already grown plants. The density is about 30 plants per square metre. The watering is provided from the top. Tap water must be supplemented with nutrients. Watering and fertilization are automated. The whole weight of the Vertical Garden, including plants and metal frame, is lower than 30 kg per square metre. Thus, the Vertical Garden can be implemented on any wall, without any size or height limitation.
THE VERTICAL GARDEN ALLOWS people to re-create a living system very similar to natural environments. It's a way to add nature to places where man once removed it. Thanks to botanical knowledge, it's possible to display natural-looking plant landscapes even though they are human-made. In any city, all over the world, a naked wall can be turned into a Vertical Garden and thus be a valuable shelter for biodiversity. It's also a way to add nature to the daily life of city inhabitants. Besides, thanks to its thermic isolation effect, the Vertical Garden is very efficient and aids in lowering energy consumption, both in winter (by protecting the building from the cold) and in summer (by providing a natural cooling system).
THE VERTICAL GARDEN IS ALSO an efficient way to clean up the air. In addition to leaves and their well-known air-improving effect, the roots and all the micro-organisms related to them are acting as a wide air-cleaning surface with the highest weight to size efficiency. On the felt, polluting particles are taken in from the air and are slowly decomposed and mineralized before ending up as plant fertilizer. The Vertical Garden is thus an efficient tool for air and water remediation wherever flat surfaces are already extensively used for human activities.
