Components of vertical greenery systems – The green wall

green wall selectionThe concept of vertical greenery systems is deceptively straightforward. Horizontal shrubbery is transposed onto a vertical array. 
Green wall systems are commonly categorized into carrier (casement/cassette/modular pots) and support systems (creepers) (Nparks, 2009). Figure 1 illustrates the difference between the two systems. The focus of this article is on carrier systems.

The effectiveness of a vertical greenery system depends on several factors, such as:

1. Plant and substrate system
2. Light provision
3. Plant selection
4. Irrigation
5. Maintainability

The first problem often encountered by architects and designs is Point 1, choosing a green wall system. Points 2 to 5 are often included in the green wall sales package. The one question to answer will be:

“Which green wall system is the best?”

Well, they are all as good, or as bad. Sales personnel will tell you the same thing: that their proprietary system is the best in the market. It can be confusing to navigate through the sea of sales pitches that is ultimately geared towards a purchase. But if we are to determine the effectiveness of vertical greenery systems with the criteria stated above, then it becomes a tad more objective.
It is important to note that Points 1 to 4 are largely independent variables, that is to say they are not significantly related until you consider Point 5. Therefore, when we choose a green wall system, we do not expect it to solve all issues to do with plant selection, or irrigation. To facilitate the selection of an appropriate green wall system (Point 1), we will have to rephrase the question to:

“What should I consider when choosing green wall systems?”

There are many types of vertical greenery systems in the market today, and they offer different functionalities and support for different plant types. For the purpose of this discussion, we will illustrate our points using a generic 50 cm X 50 cm panel system and a generic modular pot system. We will limit the discussion to the following:

a. Effect of system on plants

b. Effect of system on substrate

c. Effect of system on maintainability

Effect of system on plants

How does the green wall system carry its plants? Let us consider the Selaginella genus (Figure 3b). These are mat-forming perennials growing up to 5 to 10 cm tall, bearing small, scale-like leaves giving a fern-like appearance. These plants grow well on the ground as well as on big 50 cm X 50 cm green wall panels (Figure 2).

However, plants from the Aglaonema genus (Figure 3a) are more shrub-like and tend to grow upwards. This will present loading issues for panel systems. Modular pot systems will be more suitable as there is provision for the plant to naturally grow upwards without compromising the integrity of the green wall substructure (Figure 2).

UGL is collaborating with Chop Ching Hin Pte Ltd to compile a list of plants and their suitability on different green wall systems.

Effect of system on substrate

How does the green wall system hold its substrate? If a green wall has no capability to hold its own media, or allow plants to hold and grip on the system, it will be very difficult for the plants to establish itself on the wall. Some panel systems require pre-growing in the nursery for a period of time before installation. This means a time lag between ordering the plants and actually conducting the replacement. When plants are just stuffed into the system, the amount of stress subjected to the root ball is immense. This often leads to very low survival rates for replacement plants (Figure 4).

Effect of system on maintainability

In recent years, many people in the landscape industry have been trying to answer the question of green wall maintainability. There is really no clear answer to that. While some claim to have zero need for maintenance for their green wall products, our view is that as long as plants are involved, be it on the ground or the wall, it will definitely require some form of maintenance.

A common form of maintenance is replacement of plants. An effective green wall system will facilitate this process. If we consider the weight of a 50 cm X 50 cm panel (50 Kg) and a modular pot system (1 Kg), the modular pots will definitely be easier to replace. This will different implications with regards to labour, cost and safety.

There are, of course, many other considerations that we are not able to cover in this article. If you are interested to know more about green wall systems, please contact us at uglab.sg@gmail.com for more information.

We will touch on other aspects of choosing an effective green wall system in subsequent articles. Stay tuned.

– Zac Toh

Note:The purpose of this article is to explore issues associated with plants and generic green wall systems. It is not the intention of the author and the administrators of this website to promote or to denounce any particular vertical greenery system or landscape services.

References:

National Parks Board, Vertical greenery for the tropics, 2009.

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