Vertical Greenery
Good Practices
Accessibility for Maintenance
Designing a building with an early understanding of living walls can greatly reduce maintenance costs. The usual requirements of pruning, feeding and watering will be required. Firstly, the maintenance method of the green façade must be considered. For green walls extending more than 10 metres above ground level, a gondola can be used. If gondolas were to be used, there must be the presence of fasteners which will then allow for the cable to be tied and for the gondola to be secured. However, it is very risky to use gondolas for maintenance in windy conditions, as gondolas are known to have mechanical failures, swinging and striking objects and workers falling off from the gondolas. Therefore, for green facades which are situated on the higher levels of the building where it tends to be very windy, the use of gondolas should be prohibited. Alternatively, these higher green walls can be maintained from a roof-mounted work platform. For shorter green facades, within a few metres of the ground, a mobile work platform at ground level is probably the most efficient solution for access. However, ropes and roof-mounted attachments may be required for larger areas or higher buildings.
Frequency
The frequency of maintenance must be considered during the design stage as well. If the plants selected or the system chosen for the green façade requires more frequent maintenance to be done, then there must be ease of access for the worker to conduct the maintenance:
- Establishment Maintenance – maintenance occurs during the first one to two years after installation and is undertaken to fully realise the design intent and outcomes. For vegetation, this includes tasks such as pruning, weed control and irrigation to ensure healthy and vigorous plant growth.
- Routine or Recurrent Maintenance – includes regular works that are undertaken to ensure the green façade is maintained to a minimum or required standard of appearance, functionality and safety. For vegetation, this can include tasks such as weeding, pruning and removal or leaf litter.
- Cyclic Maintenance – is scheduled interventions at less frequent intervals that maintain infrastructure. It includes maintenance of the underlying building structure and of specific components of the green façade. This may include infrequent pruning or other formative management of woody vegetation such as coppicing, or annual treatment of decking or other hard landscape elements to maintain their safety and functionality.
- Reactive and Preventive Maintenance – is undertaken when some component of the system fails suddenly, or shows signs of imminent failure. Failure may be due to a long-term problem that has gone undetected (such as blocked drains by tree roots), or sudden damage resulting from an extreme weather event (such as stormwater incursion). A list of the typical maintenance activities for green facades are listed in the table below, to give a better idea on how frequent the green wall requires maintenance.
Maintenance Objective | Task |
Maintain planting design | Plant replacement, infill plantings |
Maintain plant growth | Remove waste plant material (leaf litter, prunings, weeds), inspect for signs of pest or disease and treat as needed, make seasonal adjustments to irrigation volume and frequency as needed. Ensure adequate nutrition levels for plants, inspect after severe weather events (e.g. wind or heat) to look for signs of stress |
Minimize weeds | Mulching, weed control |
Manage lawns | Regular mowing, annual renovation |
Maintain trees | Regular pruning, annual tree inspection, brace and support as needed |
Maintain climbing plants | Vigorous pruning to renew stems and encourage basal growth (every 5-7 years) |
Monitor plant performance | Maintain records of plant health, vigor and coverage, pest and disease impact |
Maintain substrate | Top-up of growing substrate may be required due to wind, rain or animal activity (check the depth of the growing substrate before any additions are made to ensure weight loadings are not exceeded) |
Maintain irrigation (and fertigation) systems | Manually test and inspect the irrigation system regularly and monitor any automated systems (check volume of irrigation delivered, its frequency, substrate moisture content, and, for hydroponic green walls, nutrient levels in the water supply) |
Monitor plant nutrition | Maintain a log of fertilizer additions and records of pH and electrical conductivity values before and after addition of fertilizer |
Maintain drainage | Ensure roof drains are clear and functioning, remove dirt and other deposits from drain inspection chambers, check plumbing hardware, check condition of fiber sheet and deeper layers if necessary |
Maintain non-vegetated zones | Remove vegetation form perimeter zones and around other equipment and fixtures |
Maintain wind protection features | Check the condition and fit of protection systems |
Maintain safety systems | Check safety anchor points for fall arrest systems, check access points, e.g. ladders and stairways, check electrical safety of power points, lighting and irrigation control systems |
Maintain waterproofing | Inspect flashings over waterproofing membrane terminations, inspect wall fabric for any damage from water, fertilizer or plants, conduct leak detection of waterproofing on a green roof – if possible |
Maintain other hardscapes | Clean or oil decking or furniture, inspect green wall or façade support systems for any loose attachments or fittings |
Human Traffic
While considering of the frequency of maintenance, the amount of human traffic should be taken into consideration as well. These two elements are inter-related, when the frequency of maintenance of the green façade is high, then human traffic around it should be low, so that maintenance can be done smoothly and affecting few people as possible, and vice versa.
Location of Vertical Greening
Vertical greenery must be adapted to the setting’s climate, as the high humidity, rainfall and inconsistent climate will definitely have an impact on the greenery system. The vertical greening can be located both internally and externally of the building. In both cases, there are different considerations to be made.
- External Vertical Greening- the vertical greening is exposed to the outdoor elements such as the outdoor temperature and weather, one important consideration is whether the façade is south or west facing. This is important because it affects the type of plant and special care that needs to be taken cared of as this wall might be over-exposed to sunlight.
- Internal Vertical Greening – the façade is located within the building and faces indoor conditions such as air-conditioning temperature and the extent to which the façade is able to attain sunlight. Such considerations will affect the plant type for the façade, where plants that are more resilient are to be used.
Availability of Natural Elements
- Lighting -if there is insufficient ambient lighting, then artificial lighting must be installed, shining onto the green wall. Lighting green walls is highly specialized, requiring the services of a lighting designer or engineer. Plants require very specific lighting quantities and qualities to photosynthesize, grow, flower and develop appropriately. Extensive knowledge of horticulture and design of green wall systems is needed to choose the right species for the light levels available on site.
- Water Supply-this includes the irrigation method as well, where the plants must receive sufficient water, since it is not possible to attain water naturally from rain or precipitation. The irrigation needed depends on the type of system, plants used and climatic conditions. Irrigation water can be enriched with nutrients, fertilizers, minerals, phosphates, amino acids or hydroponic materials to improve the vegetation development and vivacity. Some modular living wall systems which are in the form of trays include a recess in the top face of the module to insert the irrigation tube. The trays include several holes in the recess for watering the growing media by gravity 28;29;30;31. Drainage holes located in the trays bottom are used to allow excess water to irrigate the modules underneath. The irrigation tubes and connectors can be produced in several materials (e.g., rubber, plastics, piping thermoplastic, silicone and irrigation hose) containing different outputs (e.g., drip, sprinkler, holes, pipe) with distribution and intensity adapted to the plants irrigation needs. The irrigation system can also include a filtration system to prevent clogging. Moreover, various strategies applied for minimizing the consumption of treated water such as the rainwater recovery from the building roofs22; the reuse of the fluid collected in the drainage system32 and the monitoring of water supply needs29 through the installation of sensors33;34 that control the collecting water tank level, the irrigation time and weather conditions (e.g. quantity of rainfall, humidity, temperature, atmospheric pressure). In addition, the installation of a gutter in the system base to recover excess water stored in it and then reintroducing it into the irrigation system is another water saving strategy that is used in either modular35;36 or continuous33;34 living wall systems. In addition, another strategy consists in the application of sensors in the growing media for nutrients needs quantification that is important to minimize nutrients consumption and match the plant’s needs.
- Air Movement – air movement around the foliage is important to help prevent fungal growth, thus additional ventilation may be needed to ensure sufficient air movement for indoor walls. Outdoor walls usually create their own microclimate that creates enough air movement, but in very sheltered positions, attention should be given to this issue.
- Drainage – a good drainage system is required for both indoor and outdoor green facades, to prevent accumulation of water at the bottom of the façade. This means that during the design stage, there must be a drainage system and certain gradient in the flooring, so that water can flow into the drain smoothly. Catchment area for dripping water or fallen leaves should be installed and considerations concerning water ponding and other slip risks are needed. A drip tray system can be installed above the floor level and extended outwards from the wall will address this issue of water ponding on floors. In addition, continuous and modular living wall systems use geotextiles to encourage drainage along the permeable membrane while preventing roots proliferation. The modular trays take advantage of the overlap of modules and materials to improve drainage and water excess. To achieve a better drainage, the bottom of a modular system can be concave, inclined, perforated or be made in a porous or absorbent material29. There are other examples of vessels using a filter material applied at the bottom of the module such as inoculated sand or other means to purify rainwater, remove toxins and heavy metals37; or a granular inert filler (e.g. expanded clay, expanded slate, gravel)38 which promotes the drainage and development of roots. Some examples of modular systems also use the insertion of grooves or holes on the sides and back face of modules, for better aeration and removal of excess moisture contained in the substrate22;40.
Plant Selection
The appropriate vegetation depends on climatic conditions, the building characteristics and the surrounding conditions, in which the green wall is inserted. Living wall systems allow the development of new aesthetical concepts of green walls, based on the creation of artistic solutions with plant species, exploring the use of patterns, variations in color, texture, foliage forms and density, vitality and growth. These solutions brought a wider variety of plant species to green walls, allowing the integration of shrubs, grasses and several perennials as long as their watering and nutrient needs are taken into account.
Hydroponic systems make possible the growth of a wider variety of plants, in different states of development: grown plants, cuttings or seeds39. In these cases vegetation is selected according to the desired aesthetic effect22;38, requiring the appropriate irrigation and nutrients for an adequate plant development. Therefore, it is important to analyze plants development, color, blooming, foliage and the global plant composition according to the artistic intentions to a certain building (e.g. building framing in the urban context, advertisement of a particular company, or marking distinction of an certain building or interior space).
However, in order to fulfill sustainability goals, vegetation must have low irrigation needs (e.g., use of native plants), be adapted to local conditions of exposure (e.g., sun, semi-shade or shade) and weather conditions (e.g., wind, rainfall, heat, drought and frost). Recent examples of modular LWS include the option of using succulent carpets in green walls instead of perennials and shrubs. The use of drought tolerant plant species as succulents41 reduces the needs of irrigation. These plant species have also low maintenance and contribute to the minimization of the system weight.
Another type of plant used is the ‘Tristellateia Australasiae’, which is a vine type of climber. The plant thrives in tropical and monsoon climates, making it extremely suitable for use in tropical settings. Although this type of plant is able to grow relatively fast, in order to accomplish the desired spectacular coverage, a total duration of three years is required.
As an example, the plethora of plant species used in the Rainforest Rhapsody (Figure 7) demonstrates excellent management of plant selection and placement. The bird’s nest fern and the screw pine, which both require full-sun to semi-shade, are generally found to be placed near the top of the green wall to capitalize on the natural lighting. Correspondingly, the full-shade plant davallia denticulate is placed close to the bottom of the wall; benefiting from both being the furthest away from direct sunlight and from the cover of the plants above it.
It is evident that the choice of plants for the green wall is carefully curated based on whether the characteristics of their growth and maintenance are suitable for the indoor climate they are to be utilized in. From the table below, it can be deduced that the plants are selected because of their moderate watering requirements. The plants selected are also characterized by their ability to thrive in semi-shade. By taking advantage of this, routine maintenance is greatly reduced over the lifespan of the wall.
FAMILY | PLANT SPECIES | FULL-SUN | SEMI-SHADE | FULL-SHADE | LITTLE WATER | MODERATE WATER | ABUNDANT WATER |
Acanthaceae | Thunbergia grandiflora (a.k.a Skyflower vine) | X | X | ||||
Acanthaceae | Strobilanthes dyerianus (a.k.a Persian shield) | X | X | ||||
Alliaceae | Allium fistulosum L. (a.k.a Bunching Onion) | X | X | ||||
Apocynaceae | Dischidia nummularia (a.k.a Button leafer Dishidia) | X | X | X | |||
Apocynaceae | Dischidia ovata (a.k.a Watermelon Dishidia) | X | X | ||||
Apocynaceae | Dischidia rescifolia (a.k.a Million hearts) | X | X | ||||
Apocynaceae | Hoya lacunose | X | X | X | |||
Apocynaceae | Hoya multiflora (a.k.a shooting stars) | X | X | X | |||
Apocynaceae | Hoya obscura | X | X | X | |||
Apocynaceae | Hoya verticillata | X | X | X | X | ||
Apocynaceae | Telosma cordata | X | X | ||||
Araceae | Aglaonema costatum f. Foxii (a.k.a Chinese evergreen) | X | X | ||||
Araceae | Caladium lindenii | X | X | ||||
Araceae | Scindapsus pictus (a.k.a Silver money plant) | X | X | X | |||
Araceae | Syngonium podophyllum | X | X | X | |||
Araceae | Philodendron ‘Gold’ | X | X | ||||
Araceae | Dieffenbachia Amoena (a.k.a Besar Putih) | X | X | ||||
Araceae | Philodendron erubescens ‘Gold’ | X | X | ||||
Araliaceae | Polyscias fruticosa dwarf (a.k.a Parsley Panax) | X | X | X | |||
Araliaceae | Schefflera arboricola (a.k.a Dwarf Umbrella Tree) | X | X | X | |||
Aristolochiaceae | Aristolochia acuminate Lam. (a.k.a Indian Birthwort) | X | X | ||||
Asparagaceae | Asparagus densiflorus ‘Sprengeri’ (a.k.a Sprengeri fern) | X | X | X | X | ||
Bromeliaceae | Cryptanthus bivittatus | X | X | ||||
Cactaceae | Epiphyllum anguliger | X | X | X | |||
Cactaceae | Epiphyllum guatamalense | X | X | X | |||
Convolvulaceae | Ipomoea mauritiana | X | X | ||||
Davalliaceae | Nephrolepis exaltata (a.k.a Boston fern) | X | X | X | |||
Davalliaceae | Davallia denticulate (a.k.a Rabbit’s foot) | X | X | X | |||
Dillieniaceae | Tetracera indica | X | X | ||||
Gesneriaceae | Aeschynanthus parvifolius (a.k.a. Lipstick plant) | X | X | ||||
Gesneriaceae | Episcia fimbriata ‘Blue Heaven’ | X | X | X | |||
Gesneriaceae | Episcia cupreata ‘Cleopatra’ Easterbrook | X | X | X | |||
Gesneriaceae | Aeschynanthus speciosus hook (a.k.a. Lipstick vine) | X | X | ||||
Haemodoraceae | Xiphidium caeruleum | X | X | X | |||
Lamiaceae | Mentha cultivar | X | X | X | X | ||
Leguminosae | Clitoria ternatea (a.k.a. Blue Pea) | X | X | ||||
Leguminosae | Arachis pintoi (a.k.a. Yellow Peanut Plant) | X | X | ||||
Leguminosae | Bauhinia kockiana (a.k.a. Kock’s Bauhinia) | X | X | ||||
Lomariopsidaceae | Bolbitis Heteroclita | X | X | ||||
Malphigiaceae | Tristellateia australasiae (a.k.a. Maiden’s Jealousy) | X | X | ||||
Melastomataceae | Dissoties rotundifolia (a.k.a Spanish Shawl) | X | X | X | |||
Oleandraceae | Nephrolepis falcata (a.k.a. fishtail fern) | X | X | ||||
Pandanaceae | Pandanus amaryllifollius (a.k.a. Fragnant Pandan) | X | X | X | X | ||
Piperaceae | Peperomia scanden ‘variegata’ | X | X | ||||
Polygonaceae | Antigonon leptopus ‘Album’ | X | X | ||||
Polypodiaceae | Dynaria quercifolia (a.k.a Oak Leaf Fern) | X | X | X | X | ||
Pteridaceae | Pteris ensiformis ‘Victoriae’ | X | X | ||||
Rubiaceae | Hoffmannia refulgens (a.k.a. Taffeta Plant) | X | X | ||||
Selaginellaceae | Selaginella kraussiana ‘Brownii’ | X | X | X | |||
Selaginellaceae | Selaginella plana | X | X | X | |||
Selaginellaceae | Selaginella willdenowii (a.k.a. Peacock fern) | X | X | X | |||
Solanaceae | Capsicum Frutescens (a.k.a. Chilli) | X | X | ||||
Urticaceae | Pellionia repens | X | X | X | |||
Urticaceae | Piliea microphylla (a.k.a. Artillery plant) | X | X | ||||
Urticaceae | Pilea nummularifolia | X | X | X | |||
Xanthorrhoeaceae | Dianella ensifolia (a.k.a. Common Dianella) | X | X | X | X | ||
Zingiberaceae | Kaempferia pulchra (a.k.a. Peacock ginger) | X | X |
Replaceability
In terms of replaceability, plants can be easily cut off via the vine itself. The soil and the plant in any planter box can be dug out without much difficulty. Should there be a need to replace a particular planter box due to damages or other reasons, the affected planter box can be removed easily.