Vegetation choices depend on the purpose and type of the green roof, wall or facade. A successful green roof, wall or facade planting will be based on robust, reliable species that are known, or likely, to tolerate the area’s temperatures, winds and rainfall. Look for species that perform well in challenging locations: these may be good candidates.
Ensure that species are not prone to pest infestation or disease. Avoid species that are an irritant or poisonous, or that are prone to nutrient deficiency or toxicity. Species that are weedy or that have weed potential should be avoided.
Plant selection for green roofs and facades is highly related to growing substrate. It is important to consider how deep the substrate will be – which, in turn, is determined by the weight loading capacity of the roof or facade, and the project budget. The depth of substrate influences the size of plants that can be grown and, to some extent, how much water will be available for the plants. Certain types of substrate will hold more or less water. See Substrate Properties for further information on substrate properties that influence plant growth.
Substrate is not such a constraining factor for green walls, as these tend to be engineered to suit the plant species chosen. Epiphytes and lithophytes, plants that do not require soil, are often used on green walls and can grow to mature sizes. Even species that normally do grow in soil can be grown with no substrate through a hydroponic system.
Plant selection must consider maintenance requirements of different plants and their desired appearance; for instance, manicured versus natural. Maintenance needs will be determined by the preferred look and performance of the end result and a willingness to meet the costs involved.
Species that are prone to grazing by possums or damage by birds may not be suitable. Select the most robust species possible, in keeping with aesthetic and other design aims of the project.
Plants can be sourced from retail nurseries, grown at home, or ordered on contract from wholesale nurseries for large projects. Be aware that many retail nurseries do not have experience with green roofs, walls and facades, but requesting plants with particular characteristics, as outlined on the following pages, should assist. For large green roof, wall and facade projects it is important that plant orders are placed early – wholesale nurseries prefer three to six months’ notice when hundreds of plants are required. It is important to insist that weed free ‘sterile’ growing media is used in propagation.
See the following pages for more information on