Green walls are most often made by fixing panels directly to a wall or to a framework which supports them. They are therefore either attached to existing walls or built as freestanding structures. Often, but not always, freestanding types are anchored to walls in various places to provide additional stability and strength. Green walls can be made using different types of media and planting modules.
Loose media
Green walls can be constructed using loose media in which the plants grow. The media used is usually a lightweight mix including some less dense materials such as perlite or vermiculite. These systems can comprise pot-type containers suspended in frameworks or shelf-like units, or they can be a series of planting bags or pockets made into a single panel. Pocket-type systems are usually constructed of woven fabrics or polyurethane.
Mat media
Felt and coir fibre are most often used to create substrates for mat media. They are thin panels which can be used in layers.
Sheet media
Sheets are usually made of polyurethane which unlike other substrates does not biodegrade. In a typical assembly two sheets are used with a space in between through which irrigation lines are placed. A waterproof membrane is fixed to the side which abuts the wall and the whole panel is fixed to the wall by attaching to wire mesh or brackets. Pockets may be cut into the surface and bare-rooted plants inserted.
Block media
These are manufactured media blocks in various sizes. A range of different types of compressed media may be used. Also called structural media, they can be made to fit a wide range of installations.
Different manufacturers produce a range of offerings based on all of the above. Some have elements of each type of arrangement. Many of these are modular systems and others are produced as prefabricated panels that are custom-built to fit specific locations.
In systems using fixed media substrates, an irrigation system may be set up at the top of the panels so that water is dripped down onto the plants. With systems that incorporate loose media it is more usual for irrigation drippers to be fed to each pocket or container. However, irrigation is often designed in situ to optimise efficient water usage.
Design Considerations
Green wall gardens pose a variety of challenges for the garden builder:
The higher the plants on a wall, the more weight and downward pressure exerted on the bottom of the garden, or the structure holding it.
Water which must be provided to grow the plants will increase the overall weight when it is applied.
Water run-off will gather at the base of walls so adequate ground drainage is needed, such as a gravel-filled spoon drain to channel water away from the foundations of buildings.
It is important to avoid damage to any structure that plants are attached or adjacent to. Buildings that are designed without a green wall in mind may need structural reinforcement to compensate for the added weight and associated stresses if a green wall is built as an afterthought.
Similarly, any surface used to support plants will need to be waterproof. Whilst buildings are designed to be waterproof some walls will not withstand continual water dripping down them. Interior walls are not usually made to withstand continuous exposure to water and so may need closer scrutiny and preparation. It may be better to use freestanding green walls in these situations.
Green walls must not pose a threat to people below. They must be structurally sound so they do not collapse.
Plants used must not produce heavy fruits or branches if there is a risk of these falling onto people passing at ground level.