How to Build a Green Wall

Vertical gardens are often used in city environments, to both improve the aesthetics and environmental characteristics of tall buildings; both in exterior and interior situations.

Types of Green Walls
There is no universally accepted way of classifying different types of living walls. The differences between different walls can sometimes be blurred; but it may be helpful to consider the following different types of vertical gardens.

Free Standing Living Walls
Here the vegetation is growing independent to any wall behind it. This could be either:

  • A series of container grown plants where the containers are arranged vertically on a frame, or
  • Climbing plants growing up a trellis or framework which is attached to posts, pillars or poles.

Attached Living Walls
Vegetation is growing attached to the wall of a building, a free standing wall or a fence.

Retaining Walls
These may be built into a mound slope. They could be the walls of a raised garden bed.

  • Plant roots could be penetrating through the face of the wall, into the earth or media behind the wall, or
  • Roots might be contained within pockets created in the wall itself, or
  • Plants may be rooted into soil at the top of the wall, then hang over the top, sprawling below to cover the wall, or
  • Plants might be climbers rooted into the ground at the bottom of the wall, growing up to cover the wall.

Living Facades
Here the living plant provides a green façade to a structure (usually a building).
Examples might include:

  • Climbers that attach themselves to a wall (eg. Ivy, Ficus pumila, Virginia creeper).
  • Other plants that are trained to grow in a vertical plane against a wall. (eg. espaliers)

Narrow Profile Green Lines
Wires or other supports can be arranged in various types of patterns in front of a wall (eg. To create a series of large triangles or parallel 45 degree lines from bottom to top. If these wires are arranged far enough apart and an appropriate plant is grown along them, it is possible to create attractive geometric lines of living greenery against the backdrop of a wall. This type of green wall may or may not need routine clipping (depending upon closeness of wires, and species used).
 

Design Considerations

There are two main purposes that can be fulfilled by using green walls, and the designer needs to consider both and the relative reasons for creating the green wall. These reasons are broadly:  

  1. Aesthetic
  2. Functionality


Aesthetics

Aesthetics is improved by obscuring or decorating ugly or undesirable views. A very large wall can be stark; some types of building materials can appear overpowering or undesirable in some way.
Even using small amounts of vegetation (that only partially obscure the view) can soften a harsh image or improve the visual appearance in some other way.

Functionality
Vegetation can contribute toward improving the temperature and air quality inside a building. It can reduce glare and noise, and slow the movement of wind and water.


Considerations

Consider the following when considering a vertical garden:

  • Height - how high do you want it to be? If you want it to provide privacy it will need to be at least 1.8m tall. If you want it simply to define parts of a garden, without impeding views then it might only be 30cm or so high.

  • Structural materials – are you attaching it to an existing structure or creating a new structure? How capable is the structure to support the plants? What is the load and will reinforcement of the structure be needed? Different materials will vary in strength, appearance, cost, lifespan, construction methods, and maintenance requirements. How much time, effort and money are you prepared to spend?

  • Aesthetics - will it visually suit (fit in) with its surrounds?

  • Density - will the vegetation be solid or see through. Can air flow through (ventilation can help plant health, and may reduce structural load) A more solid blanket of ventilation can subject a structure to greater forces in windy weather.

  • Thickness – how thick will the green wall be?  Some types of vegetation can hug a wall without encroaching on the ground space below; while others may be thicker (which can be a problem if there is limited space –for example, installing a green wall in an alley way can restrict vehicle or pedestrian access) This will often depend on the types of materials being used in the walls construction, and to what use you are putting the wall too (e.g. freestanding wall versus retaining wall).

  • Drainage will be an important factor for some types of walls, particularly indoors, where any water runoff can become a safety issue if it creates wet and slippery floors. Will you need to install drainage systems behind retaining walls, and may need to install drains at the base of any larger vertical garden.

  • Changes that may occur over time to the microclimate of the green wall. Shade from existing or proposed buildings, reflection off or through windows at certain times of the day, moist area created as plants grow (e.g. which may cause mould to grow), nearby trees that could change the wall environment as they get bigger, etc.

  • Don’t use plants with heavy weight or thick growth habits on wooden structures that can be less capable of supporting heavy weights.

  • When the height of a green wall façade is higher than 18metres, there can be a tendency for the growth at the bottom to widen more than the growth at the top.
  • Shading the walls of a building can decrease the temperature fluctuations inside the building by as much as 50%.

  • Research from NASA shows that plants can remove significant quantities of organic pollutants from the air, and that Hedera helix is one of the most effective species at doing this.

  • Some plants may attract birds to nest, which can become a pest problem. Narrow profile climbers are less likely to create this problem than dense intertwining plants.

Problems to Avoid

  • Using supports that are not sturdy enough for the plant species selected.

  • Not allowing for long term growth such as thickening of stems, which can eventually become ugly and heavy.

  • Not installing appropriate or sufficient number of attachments to a wall (e.g. Dyna bolts holding wires).

  • Not maintaining either the building or the plants properly.