Green Walls and Roofs

Course CodeBHT256
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment

Vertical and Roof Gardens are Increasingly Popular

This is particularly so in urban, industrial and commercial areas, where space is often at a premium, and air pollution can be a problem.

There are lots of different reasons for creating a vertical garden or roof garden, and the way you develop the garden may be affected by the reason you create it. Common reasons might be:

  • Lack of space for a more extensive garden
  • Improve aesthetics of an ugly place (wall or roof)
  • Improve physical environment (eg. Reduce glare, modify temperature, filter air pollutants, reduce water run off and mitigate flood problems)
  • Urban farming – growing crops in an urban area

Lesson Structure

There are 9 lessons in this course:

  1. Scope & Nature of Roof and Vertical Gardens
  2. Construction Functional and Appropriate Vertical and Roof Gardens
  3. Climbing Plants and Structures for climbing
  4. Plants Suited to Roof and Vertical Gardens
  5. Adaptations for Other Plants in Roof and Vertical Gardens
  6. Container Growing
  7. Maintenance –watering, pest control
  8. Applications/Landscaping –Roof Gardens
  9. Applications/Landscaping –Vertical gardens


  • Discuss the nature and scope of vertical gardens and roof gardens in horticulture today.
  • Explain engineering considerations involved with the building of vertical and roof gardens, both on small and large scale projects.
  • Select appropriate materials and plan the way in which the non living components of the garden is created, in order to achieve an appropriate and sustainable installation.
  • Select appropriate climbing plants for creating vertical or roof gardens, and determine appropriate strategies to cultivate those plants, in a variety if different situations.
  • Select appropriate plants for use in vertical or roof gardens, which are tolerant of the adverse growing conditions, having natural adaptations to growing under conditions that are encountered in these gardens.
  • Select and plan the cultivation of plants that lack natural adaptations to growing on roofs or vertical gardens; but which are none the less required to grow in these adverse conditions
  • Explain a range of container growing techniques, in a range of different roof and vertical gardens, that may be used with a selection of different types of plants.
  • Identify and evaluate problems with vertical and roof gardens, and compare options for solving those problems
  • Plan the development of roof gardens for both small and large scale applications.
  • Plan the development of vertical gardens for both small and large scale applications.

What is a Vertical Garden?

A vertical garden is a garden where the plants are growing and thriving on the vertical rather than the horizontal plane. There are a range of variations on this concept. 

For instance, a climber on a fence or wall or a series of containers supported one above another, growing plants to create a vertical layer or wall or curtain of vegetation which may be several metres tall. Historically, the earliest example, if indeed it did exist would have been the Hanging Gardens of Babylon which were reportedly built by Nebuchadnezzar II for his wife Amytis at a site near Al Hillah in Iraq. They were thought to be a series of steep terraces adorning their palace incorporating a wide variety of trees and plants to replicate the appearance of a naturally vegetated mountainside.  

Examples of vertical gardens are:

  • A screen of growth tumbling or climbing over a wall or embankment, where most of the growing medium and feeding/watering apparatus is located at the top of the wall, or on terraces part way down that are invisible to the observer.
  • A vertical and/or retaining wall with plants embedded into the structure to give support and aesthetic appeal.
  • Terraced gardens up a steep slope or incline where the terraces are close together, so that when planted, the plants grow as in one wall of colour or foliage.
  • A series of hanging baskets and pots located to produce a vertical screen. A purposefully designed and constructed sophisticated system of walling and growing material complete with automated irrigation.
  • A wall mounted hydroponic system, using NFT (Nutrient Flow Technique). Climbers on a trellis attached to a wall or fence, trained to grow up or hang downwards.
  • Custom-built frame supporting containerized plants in a vertical plane.
  • Espaliers.

What is a Roof Garden?

  1. Roof gardens seem to fall into three types
  2. Ones designed to cover a garden shed or relatively small area of roofing.
  3. Gardens designed to cover a complete building, or most of its roof.

Gardens to be used, located on a roof because it is accessible and functional space.

Small Scale Roof Cover
These gardens may be created to soften the aesthetics, hide an ugly construction, create a more environmentally friendly space; or perhaps a combination of all three. They are rarely intended as a place to be visited and used by people. They are too small for that. Birds and other animals (even cats), may however visit this type of roof garden. These gardens may be nothing more than a cover of sedum or some other low growing plants, spreading out across the roof.

Large Scale Roof Cover

These are gardens created for the same reason as the previous type; but on a more extensive scale. In extremely hot or cold climates; this type of roof garden can contribute greatly to reducing heating or cooling costs within the building.

Sometimes a building might be created by constructing it against an embankment, and then covering the roof with garden, leaving access to the building through only a limited number of places. This type of building may appear largely concealed on a property; and being adjoined to an embankment, the thermal mass effect of the ground that encases the building may vastly reduce heating and cooling requirements.

Functional Roof Gardens
These may be found in commercial buildings or residential high rise accommodation, where the availability to ground level open green space is limited; but the possibility for a rooftop garden area has been identified and exploited.

This type of roof garden can be small or large; even akin to a park on a roof. It may have shrubs and even small trees, pathways, seating and any other garden features you might find in a ground level garden.  The one thing that is different though is that there is a building below the growing plants; and that fact is going to pose limitations to what might be done and the expense of doing it.

What Plant for What Roof?
Choosing the right plant for the roof is critical.

Every roof has unique and different characteristics and your choice of plant should depend upon an intimate understanding of the growing environment in which it is to be grown. Consider the following:

  • Depth of growing substrate may be one of the most limiting factors.
  • Roofs are often hotter than surrounding ground surfaces, because they may not have any shade eg. Even though the ground surface alongside a building may be in the open, it will still often be shaded part of the day by the building.
  • Tall trees can shade the walls of a building but may have no impact on the roof.
  • Exposure to wind, storms, hail, etc. can be stronger on a roof than on the ground, and this can uproot plants and tear foliage.
  • Dryness is a greater threat on a roof. Wind and heat can both dry the plant tissues and the growing media.


Opportunities on the Increase

The opportunities for green walls and roofs will only increase as our cities continue to grow.
This is a solution to environmental and commercial problems on so many levels.
Opportunities abound, whether to enhance your existing career, take your career in a different direction, start a new business or simply grow more on a property that has run out of space. 

Who Will Benefit From This Course?

  • Plantscapers and contractors in this field
  • Planting designers
  • Interior designers
  • Garden designers