Are Green Walls On The Up?

Do the benefits of putting plants on outdoor walls outweigh the cost of installation and maintenance? Carolyn De Kock reports.

An eye-catching splash of colour along the Keyes Avenue Art Mile in Rosebank, Johannesburg is the latest addition to Johannesburg’s growing collection of “green walls”. Unlike many vertical gardens that feature lush decorative plants, the Keyes’ wall is planted with veld flora, from the Egoli Granite Grassland around Gauteng’s mine belt.

Before urbanisation, Rosebank would have been covered in these types of grasses and perennials.

“Keyes Avenue is the epitome of what we’re trying to achieve. We’ve bent the rules,” says Oscar Lockwood, director of Life Landscapes, who led the installation of the project. The wall itself forms part of the exterior of St Teresa’s school.

Lockwood says that green wall technology has come a long way over the years. Early systems were made from plastic with holes cut into it, now they are scalable modular units using sophisticated engineering.

Modern green walls include automated drip irrigation and need to be maintained at grand heights, sometimes requiring machinery to enable staff to access plants right at the top. However, the long-term result is worth it, according to Lockwood.

“The amount of water used is less than if you had planted that same garden on the ground,” he says, “thanks to a drip irrigation system, which is gravity fed and runs through each planter. This ensures that water penetrates the roots, and reduces loss to evaporation.

“The Keyes Art Mile wall requires watering for two minutes every day. Any excess is collected in a drip tray at the bottom and can be reused,” Lockwood says.

Such a sophisticated system doesn’t come cheap, however.

“To build a green wall that’s going to last is going to cost,” Lockwood says. But do the pros outweigh the cons?

A study by French landscape architect Brice Rodriguez, in collaboration with the French Research National Agency, found that among the benefits of green walls is that they can reduce the mean radiant temperature by 4° C, which means that the outdoor air next to them is cooler.

This directly affects the thermal comfort of a street canyon, but green walls can also help to counter the endemic pollutants from cars, including nitrogen dioxide and particulate matter. According to landscaping group, Ambius, living green walls have been shown to reduce these levels by 40 per cent and 60 per cent.

Other benefits include noise reduction and muffling of high-frequency sounds and the ability to cool down the interior of buildings through evapotranspiration. This minimises the need to use air conditioning.

Greening indoors

Our indoor environments are even more toxic, and benefit even more from vertical gardens. According to a study published in the journal, Science of the Total Environment, indoor toxins include formaldehyde, VOCs, trichloroethylene, carbon monoxide and benzene, which emanate from detergents, furniture, varnishes and plastics to name just a few. An indoor green wall is the most effective way to improve air quality in buildings. Office spaces can even rent green walls, making it more affordable.

Vertical gardens also offer homeowners a cost-effective way to landscape smaller spaces.

“Traditional gardens are becoming a luxury that few can afford. This creates opportunities for green walls to be installed in spaces where traditional gardens are not possible,” says Ricky Frankental, owner of Vicinity, a green wall manufacturer. “The residential market is steadily growing as people see more successful projects in offices, hotels and retail stores. The DIY market is starting to develop as gardeners want to take on the challenge of building their own green walls.”

Plant selection is critical, according to Frankental, and depends on the location of the wall.

“Our system is basically a way of stacking pot plants. So the normal gardening rules of planting up a pot that can handle the conditions of the space where it is going to be placed apply.”

You might be interested in these articles?