Living walls, or green walls, are self-sufficient vertical gardens that are attached to the exterior or interior of a building. They differ from green façades in that the plants roots are in a structural support fastened to the wall itself; the plants receive water and nutrients from within the vertical support instead of the ground. The vegetation can partially or completely cover the wall; these green walls may be indoors or outdoors, freestanding or attached to an existing wall, and come in a great variety of sizes.
Green walls are often constructed of modular panels that hold a growing medium and can be categorized according to the type of growth media used: loose media, mat media, and structural media.
Loose medium walls tend to be “soil-on-a-shelf” or “soil-in-a-bag” type systems; they have their soil packed into a shelf or bag, and are then installed onto the wall. These systems require their media to be replaced at least once a year on exteriors, and approximately every two years on interiors. Loose soil systems are not well suited for areas with any seismic activity, because these systems can easily have their medium blown away by wind-driven rain or heavy winds. These systems are best suited for the home gardener without physical media erosion systems, where occasional replanting is desired from season to season or year to year.
The second type is mat type systems, which tend to be either coir fiber or felt mats. Mat media are quite thin, even in multiple layers; as such, they cannot support vibrant root systems of mature plants for more than three to five years before the roots overtake the mat, and water is not able to adequately wick through the mats. Reparation of these systems is through replacing large sections of the system at a time by cutting the mat out of the wall and replacing it with a new mat. This process compromises the root structures of the neighboring plants on the wall and often kills many surrounding plants in the reparation process.
These systems are best used on the interior of a building and are a good choice in areas with low seismic activity. It is important to note that mat systems are particularly water inefficient and often require constant irrigation due to the thin nature of the medium and its inability to hold water and provide a buffer for the plant roots. This inefficiency often requires water re-circulation system to be put into place at an additional cost. Mat media are better suited for small installations no more than 2.5 m high where repairs are easily completed.
Finally, structural media are growth medium “blocks” that are neither loose, nor mats, but incorporate the best features of both into a block that can be manufactured into various sizes, shapes, and thicknesses. These media have the advantage of not breaking down for 10 to 15 years, can be made to have a higher or lower water holding capacity depending on the plant selection for the wall, can have their pH and EC (Electrical Conductivity) customized to suit the plants, and are easily handled for maintenance and replacement.
References
greenovergrey.com
ambius.com