Green wall systems vary greatly in their design and construction from DIY projects to modular green wall systems available to buy ‘off the shelf’, through to proprietary systems that are custom-fitted to a wall. Specialists in green wall design and installation can provide advice on the most suitable system and the best construction approach. Green walls can deliver more than aesthetic benefits, and this requires consideration in the design stage.
Hydroponic green wall systems can be either modular containers or large panels.The systems are installed via brackets that sit out from the load-bearing wall (or a stand-alone structure) to create an air gap between the wall (or other structure) and the backing sheet of the green wall system. In a hydroponic system, an inert growing medium is provided to which the plants physically anchor, such as a horticultural foam, a mineral fibre or a felt mat. These materials can act as a water retentive sponge, although the more they soak up the heavier the system becomes. The advantage of the hydroponic system is that there is no structural decay of the growing medium, no salt build up from fertilisers and nutrients are supplied in a precise and controlled manner. Over time, plant roots grow and ramify through the entire system to create a very robust network.
Substrate-based systems use substrate-holding containers made of plastic or metal. The substrate is packed directly into the empty container or placed in a water permeable, synthetic fibre bag. The containers are connected together and anchored to the wall or to an independent, structurally secure metal rack or framework. Alternatively, plastic or metal growing containers can be hung on a metal grid fixed to the wall. Individual growing containers can be removed for maintenance or replanting. Most substrate-based systems are designed for automatic irrigation, just like the hydroponic green wall systems.
The growing medium in these systems provides a structure to support the plant and facilitates water, air and nutrient access, decreasing the need for constant management associated with hydroponic systems. However, over time the reserve of nutrients will be exhausted and there can be a build up of salts in the growing medium. Traditional potting mix is not a suitable substrate for green walls. A specialist green wall provider will advise on the most appropriate growing medium for a particular green wall design. See also here for information about substrate characteristics.
Drip trays are used to capture excess irrigation water from the growing medium as well as water droplets that drip off foliage. The size of the drip tray should be sufficient to hold an entire irrigation cycle’s water volume (before draining away prior to subsequent cycles starting). Drip trays may not be necessary if the run-off is intended to irrigate vegetation below the green wall. If drip trays are not used, ensure run-off does not create slip hazards, damage the building fabric or provide excess moisture or nutrients to ground-based plantings below.
Water captured in the drip tray or reservoir at the base of the planting system can be pumped back to the top of the wall for re-use rather than being wasted, provided that it is treated to prevent build-up of nutrients. Drip trays should have a drainage pipe of sufficient diameter to empty the drip tray or manage water capture sufficiently to mitigate overflow of the tray. Fascia treatments may be added to conceal the edges and functional elements of the green wall system, such as the irrigation system and drip tray.
For more on green wall construction see the ‘related pages’ menu on the right.