Basic types of green wall
The easiest way to introduce a green wall is to mimic Mother Nature and use simple climbing (or trailing) plants. Plants are established in the ground or in suitable troughs at the base of the wall to be covered. A framework is then attached to the wall for the plants to ‘climb-up’ to provide the wall with its green covering. In the wild this is often how such plants establish themselves by using other plants or naturally formed rocks as their ‘climbing-frame’.
To aid the climbing process on buildings a number of systems exist including wire mesh frames, trellises and steel cables. The use of each frame is guided by the individual application, for example ivy plants grow easily and can attach themselves to walls and the side of building with minimal additional intervention. Often frames will be used to encourage the direction of growth or to support different species of plant growing on the wall.
Another easy way to introduce a living green cover on a wall is to plant on the top and allow growth to trail down. This is particularly effective in small enclosed areas (and even on internal walls).
Modular living walls
Though the systems used for this type of green wall are usually more sophisticated than for climbing façades, the final installation generally offers a more flexible solution in terms of aesthetics and functionality. The techniques are based around two main groups (though hybrid solutions do exist).
This technique takes advantage of the fact that plants do not require soil to grow. Soil simply provides mechanic root support for the plant and it is only water (along with the minerals stored in the soil) that is required (in addition to light and carbon dioxide from the air).
Hydroponic systems are generally grown on pre-constructed panels prior to vertical installation using a specialist growing medium as root support. When ready the panels are transported to site and attached to a framework on the side of the wall/structure to be covered. Once installed plants will continue to grow and further cover the structure.
These systems typically use moulded troughs or containers that are built on or attached to existing walls (or similar structures). Planting is supported by soil-based substrates similar to those used in green roof installations; utilising a lightweight combination of recycled materials containing the right balance of nutrients with a free-draining medium.
The natural water retention properties of most substrates allow irrigation systems to be simple in design and construction, thus lowering installation and maintenance costs. However, an associated disadvantage of substrate-based systems is their weight relative to other solutions. Newer lightweight materials are increasingly becoming available to address this issue.
There are a number of different systems available supporting many applications and budgets. Most garden centres will supply soil-based systems for vertical allotments and domestic green wall installations. A range of more sophisticated solutions exist for larger commercial green wall applications, together with a variety of irrigation solutions to suit.