The Essence of Life ...and living green walls, part 3
Water is essential to all life. It keeps us hydrated and keeps all of our vital organs functioning. You cannot live more than a few days without water. In much the same way, water is also essential for plants.
Water is therefore an important consideration for any living green wall project. It is important to know how plants use water, how to spot plants having a water-related issue, and how different types of green walls can be irrigated. In this three-part blog post, we will be examining the topic of water and how it relates to living green walls.
Nearly all living walls use the building’s standard water supply, but a few living walls have been designed to use rainwater, grey-water or storm-water. These recycled water systems are great in theory, but in practice the drawbacks usually tend to outweigh the benefits. Recycled water must be filtered and pH balanced before it can be fed to the plants. The micro-contaminants in recycled water and the altered pH levels can have very harmful effects on the plants in a living wall. The required filtration and pH balancing systems are not cheap. In addition, you are still required to have a standard water connection anyway since the supply of recycled water is not guaranteed. The secondary water line is needed as a fail-safe in the event of a drought or reduced gray water supply (i.e. weekends & holidays). Being green and recycling water is fantastic, but unfortunately green walls are not well suited for utilizing recycled water.
Drippers or Wickers
Most living walls use a system of automated irrigation lines with tiny emitters that drip water on/into the soil or growing medium. A smaller number of systems use synthetic cloth wicking systems that utilize natural capillary action to draw water up to the plant roots. Capillary wicks are simple and reliable, but because they deliver a constant supply of water you cannot easily adjust the watering for different plant needs. Drip emitter systems can be tailor made with different watering zones for different plants, but they are more labor intensive to install and there is always a risk of the tiny emitters becoming clogged.
To Recirculate Or Not To Recirculate, That Is The Question
Some living wall systems utilize a recirculating system to recycle and reuse excess water. In a recirculating irrigation system, there is a supply water tank at the bottom of the green wall that is filled from the building’s water supply. The tank water is then pumped to the vegetation in the living wall and the excess water drains down to a catch basin at the bottom of the wall and then back into the water supply tank. The system recirculated the water through the wall many times per day. The goal of these recirculating systems is to increase water efficiency and not waste as much water.
Recirculating systems are great, but they do have their drawbacks. One potential issue is with the excess water collected in the catch basin. This water can become contaminated from running through the living wall and recirculating that water can spread the contamination to the entire green wall. A single plant with a soil-borne disease can become a big problem. Another potential issue is the energy efficiency of the pumping system. Recycling the water seems like a sustainable water conservation solution, but the cost may be counterbalanced by the increased electrical demands of the pumping system.
Plant nutrition, such as water soluble or liquid fertilizer, can be delivered through the irrigation system. In a recirculating system, salt-free liquid fertilizer can be added to the water storage tank. Direct irrigation systems may incorporate a nutrition injection system to draw liquid fertilizer from a container or storage tank into the irrigation system during the watering cycle. Nutrition can also be delivered manually, depending on the type of wall.
The effectiveness and efficiency of a watering system is based on how well the water is directed to plant roots with minimal excess waste water. You don’t want to waste water, but you also don’t want to spend a ton of money or energy trying to save a small amount of water. The water use has to be balanced with the overall energy use of the system. The right answer will be different for different projects and different geographies. There are always inherent risks to using water indoors, so it is important to consider all worst-case scenarios and related risk mitigation strategies.