Drainage and irrigation

Garden beds, or at-ground planter boxes used for climbing plants for facade greening, should have drainage appropriate for the plant species selected for use. Container systems placed at elevation on the face of a building should have a free-draining growing substrate to avoid potential waterlogging in the event of prolonged periods of wet weather. The potential for ponding of water above the top of the growing substrate should be minimised by providing overflow drainage holes in the sides of the container, just higher than the level to which the container is filled. In most cases, run-off through the base of the growing containers will simply run down onto the ground beneath, but drip trays can be installed to collect water.

The vigour of many climbing plant species means that irrigation will be required to maintain high-density foliage cover and long-term performance of the green facade. In-ground plantings in domestic settings will need irrigation at least during the hotter months, if not year-round. Harvested, recycled water should be used for irrigation wherever possible. Irrigation frequency will depend on the plant species selected, the type of growing medium used, and how exposed the facade is to sun and drying winds.

At-ground plantings can be irrigated by automatic systems or manually with a hose. Surface or sub-surface dripper systems are suitable automatic systems. Irrigation supplied to elevated planters requires appropriate water supply pressure from tank, recycled and mains water supplies. See here for information about irrigation systems and methods of delivery.


Facades in containers — lessons learned

A roof garden incorporating green facades was built at Council House 2, central Melbourne, in 2006. Its design included the incorporation of 950 mm deep plastic planters, connected to a cable and stainless steel trellis (X-TEND®) mesh for growth of the facade. The intention was to increase greenery across the building through use of the roof and facades.

Unfortunately, the facade plantings have not grown well due to multiple problems with the planters, growing substrate and irrigation. The black colour of the planters leads to considerable heat gain in the root zone over summer, causing difficulties for plant growth. The planters also tend to split, the side wall plastic seemingly unable to tolerate the high bulk density of the growing substrate. Additional metal frames were used to support the replacement containers. The substrate itself has also had issues, with plants failing or growing poorly and a considerable drop in the total volume since installation. A further complication has been the irrigation system. Each planter is irrigated via combination of a valve, water reservoir and foam ‘wicking’, all enclosed in the base of the container. The valves function at a much lower pressure than the mains supply, meaning most failed when they were first operated. This in turn affected any possible ‘capillary irrigation’ upwards to the root zone in each container, leading to extensive plant death shortly after installation. Replanting has occurred but all containers now need to be hand-watered. The City of Melbourne is currently investigating cost effective options for resolving these problems.

The City of Melbourne recommends thorough research or peer review to assist and support decision-making around the design and use of new technologies.IMG_8037