In addition to shading, leaf transpiration can create a cool microclimate against the wall surface and plant foliage can ensnare airborne particulates to improve air quality. With all of these benefits it’s no wonder so many of us are inspired to get digging.
How they differ from green walls
Green walls are increasingly being installed on commercial and apartment buildings to introduce much-needed greenery to sites where there is limited access to soil. Green walls, especially the highly decorative ones, require regular maintenance and commonly use a broad range of plants, each supported by a small pocket of stable growing media (e.g. potting mix). They are irrigated and generally highly dependent on this irrigation for survival – small quantities of growing media can be insufficient to buffer the roots from heat, for example.
Green facades are inexpensive, easier to maintain and far less dependent on irrigation. The roots of climbing vines used for green facades are commonly planted directly into the garden soil with access to rainwater. And one to two plants can sufficiently cover a house facade or wall.
If you are considering establishing a green facade, then the very best place to start is by planting your west-facing wall: the late afternoon sun with its perpendicular angle makes overhead shading of walls ineffective. Any wall exposed to direct sunlight will benefit from the shading and microclimate a climbing plant can provide.
It is always important to improve existing garden soils in urban areas as they are often low in organic matter. With the addition of plenty of compost and a thick layer of mulch your plants will get off to a good start, especially if planting in summer. Winter planting requires a light sprinkling of mulch to protect the soil from the harsh battering of heavy rains.
Once you have decided on a climber, investigate its mode and method for climbing – is it self-clinging or will it need a supporting structure? Take note of its growing height and spread as this will determine how many plants you will use and how close to plant them, then be patient and focus on what will be. While the west face might be your starting point and your top priority, don’t hesitate to find suitable plants for walls with other orientions. The internet makes searching for plants extremely easy. I find the Royal Horticultural Society website very useful, and by searching for ‘climbing plants’ a broad range of other sites will appear, to help you sort through various species and cultivars.
Self-clinging vines, such as Parthenocissus tricuspidata (Boston ivy) and Parthenocissus quinquefolia (Virginia creeper*) are common plants to use as they require no structure to support them. They are popular because they produce thick growth and attach directly to masonry walls via specialised adhesive pads. They create a painterly display of blazing colour in autumn and shed their foliage in winter.
There are a number of other recommended plants that can be selected to provide self-supporting green facades. Ficus pumila (climbing fig) has dimorphic leaves where the juvenile leaves differ to the adult leaves (juvenile leaves can be retained with regular pruning). For shady areas the autumn yellowing Hydrangea petiolaris (climbing hydrangea) could be used. It has a mass of lacecap-style flowers and is dependent on moist soils – even in shaded areas it will need heavy mulching and frequent watering during summer months.
The choice of climbing vines vastly expands once you forgo the self-clinging variety and move onto species that use structural support to help them climb. One of the downsides of using climbers that need structural support is that the framework adds cost and installation time. On the upside, vines grown on a framework can often provide extra thermal protection by creating an air pocket between the plant and the wall, especially if the frame is installed to sit off the wall.
When using structural support it is essential to ensure it will last the distance. Once the climber has matured, its weight will be significant. It can take climbers many years to cover the facade of your walls, and it is very disheartening to see it fall off if its support structure is not built for longevity.
There are a variety of products on the market that are very durable. Some of these are commonly used to reinforce concrete slabs, such as steel mesh which can be bought in a galvanised or non-galvanised form.
Native Hardenbergia violacea, has deep green arrowhead-shaped leaves and bright pea-shaped purple flowers produces thick, evergreen growth that will cover a two to three metre wall all year round. Pandorea jasminoides, an evergreen warm temperate plant with trumpet-shaped flowers, will do equally well in a sheltered frost-free site in southern Australia.
There are about 400 native climbing species to choose from, although this number reduces once climate is accounted for. Other native climbers include Pandorea pandorana (tropical to cool climate), Tecomanthe hillii (tropical), Hibbertia scandens (sub-tropical, warm temperate, cool temperate, Mediterranean), Passiflora cinnabarina (temperate to tropical).
Muehlenbeckia complexa, a non-native climber with small pretty heart-shaped leaves, is also an excellent choice with its wiry interlaced stems able to reach a height of four metres.
Do plants damage walls?
While some people have expressed concerns about climbers damaging masonry walls, this is rarely the case. Walls are primarily damaged by weathering from extreme climate fluctuations. Plants will then make their way inside if the damage is not repaired. The benefits of using green facades are far greater than the risks, and when combined with trees, shrubs and grasses, green facades are a far cheaper and more beautiful way to cool your home than air-conditioning.
And it’s not just households that are embracing nature to mitigate heatwaves. Local governments are reassembling their ecological skin and now employ green infrastructure officers whose job it is to design ‘ecosystem’ services to provide clean drinking water, clean air and shade. The direction we are taking is extremely inspiring – by re-employing nature we will be better positioned to mitigate heat waves in our thermally comfortable and visually stunning homes.
* The berries from Parthenocissus quinquefolia contain oxalic acid, which is moderately toxic to mammals.
Mara Ripani of Village Dreaming is a sustainability advocate with qualifications in horticulture and environmental policy.