Vertical green walls have many of the benefits of green roof structures, but with the advantage that there are many more vertical spaces that can be covered. They are also generally more visible, enhancing the environment for more people.
Green walls can be divided into two broad categories: ‘natural’ and ‘artificial’. Natural green walls use plants that would naturally climb, such as Virginia creeper or climbers. Trellis or wires can be used to assist the plants in covering the walls. Irrigation is desirable but not essential. Generally, a drip irrigation system at the root zone will speed up coverage of the wall and reduce growth problems during drought.
For artificial green walls, irrigation is essential, as is a method of supplying nutrients. It is vitally important that the wall irrigation system is an integral part of the design, not an afterthought. Artificial systems generally have their root zones packed into frameworks hung onto the wall, with little chance of the plants obtaining a natural source of water. For these systems, such as the G-Sky green wall pictured above, irrigation and nutrients must be supplied using drip pipes built into the structure.
Irrigation control systems need to take account of the changing weather conditions, as water requirements for green walls will vary enormously depending on aspect and weather.