Green noise barriers are popular, but “green” is often used primarily as a selling point, while the quality of the vegetation often leaves much to be desired.

According to Erik Muggen of Greenwall, the intentions are usually good—on the part of the client, the designer, and the contractor alike. A noise barrier planted with greenery looks attractive; greenery filters particulate matter, absorbs CO2, and produces oxygen. Even more importantly, greenery sells. Obtaining a permit for the noise barrier is just a bit easier, and there may even be some subsidy funds available for it.

Green as a balancing item

Yet things often go wrong during implementation. Landscaping often ends up being the last item on the to-do list, and for cost reasons, the decision is frequently made to use plants that are too small, planted in street sand and spaced too far apart. The bamboo support stake is left next to the root ball, as it allows the plant to be secured to the screen, and dead plants are often not replaced in a timely manner.

The result is a noise barrier with sparse vegetation that takes years to become fully covered, and thus fails to do what it’s supposed to do: provide greenery. To prevent this kind of disappointment, Greenwall has created the GGS (Green Noise Barrier) planting model. It’s a simple and concise list of criteria that the vegetation on a noise barrier should meet. The planting model is freely available for anyone to use. Greenwall’s goal is to prevent failures and ensure that green noise barriers maintain a good reputation. Muggen: “All too often, you see a (civil engineering) contractor digging a few holes after construction, planting some Hedera in them, and handing the project over. That’s bad for the entire market for green noise barriers.”

Planting Plan

The planting model describes the quality of the plant strip along the screen; the size and quality of the plants; the method of securing them; and the finishing with a layer of mulch.

Greenwall GGS Planting Model:

• Four plants are planted per m1 of screen.
• The height of the plants is 50–75% of the height of the noise barrier, alternating with low plants in a sinusoidal pattern.
• The climbing plants have at least 3 tendrils, look fresh and strong, and have runners.
• The plant variety consists of at least 80% Hedera, possibly supplemented with other types of climbing plants such as Parthenocissus or Lonicera.
• Setup and maintenance are included.
• The 30 x 30 cm planting bed consists of fertilized potting soil containing 5–10% organic matter, has a pH of 4.5–6.5, contains N-P-K + Mg fertilizers, moisture, and air for optimal growth, and is covered with an organic mulch to suppress weeds.

According to Greenwall, planting in a sinusoidal pattern allows the screen to turn green from the bottom up the fastest. If only tall plants are used, there is a chance that only the top of the screen will turn green, and if the plants are too small, it will take a long time for the top of the screen to turn green.

While using primarily Hedera does carry the risks of monoculture—if a disease breaks out in the species, the damage is immediately severe—the advantages of Hedera for noise barriers are such that Greenwall has chosen it nonetheless. Mosquitoes: “We’re always looking for new species, but so far, no other species comes close to Hedera. The screens quickly grow dense, and they remain a beautiful green all year round.” Greenwall includes the GGS planting model as standard in its proposals to clients.