This question and answer article brings together real conversations between growers and Colin Austin, addressing the most common practical issues faced when using wicking beds. It covers greywater reuse, organic matrix choices, decomposition, nitrogen balance, pollination in shade houses, weed control, and water management across seasons. The answers are based on long-term hands-on experience and focus on simple, robust solutions suitable for dry climates and low-water systems.
Recycling Greywater in Dry Conditions
Question:
We need to recycle our greywater, which we obviously cannot use directly on vegetables. Rainfall has dropped dramatically, and as we rely entirely on tanks, we must use every possible drop or start carting water. The fruit trees are already planted and cannot be moved. Are there adaptations or systems we can use?
Answer:
Established orchards can be irrigated very effectively using open-style wicking beds. These systems allow water to move laterally through soil and organic material rather than relying on surface irrigation. I recommend reviewing examples where orchards are supplied this way, as it allows greywater to be safely processed through soil biology before reaching plant roots.
Organic Matrix Breakdown and Bed Subsidence
Question:
What stops the organic matrix water reservoir from decomposing over time and causing the bed to sink? Is it a matter of digging sections up and refilling?
Answer:
The organic material is meant to decompose. This is a feature, not a fault. As it breaks down, it releases nutrients and sequesters carbon. Over time, topping up is necessary. One method is to dig down carefully to the top of the pipe, refill with fresh organic material, and spread the excavated soil back over the bed. Each time, use a new spot.
The easier method is to compost directly on top of the bed. Watering the compost flushes nutrient-rich compost tea into the lower zone. In practice, I use both methods. Weeds pulled from the bed are placed on the compost zone, allowed to break down, and later buried.
Composting consumes nitrogen, so it is important to add nitrogen sources such as blood and bone or chicken manure to maintain balance.
Choosing the Right Organic Material
Question:
Some sources say woodchips rob nitrogen, while others suggest hay, straw, or lucerne bales, which may introduce weeds and pests. What is best?
Answer:
Weed seeds are a real issue, especially in warm climates. Composting alone does not reliably kill seeds. The most reliable method is immersion. Allow seeds to germinate in moist compost, then bury the material deep in the bed where it remains waterlogged and light-free. Germinated seedlings are easily killed under these conditions.
Geofabric and Water Separation
Question:
I have seen systems using geofabric to separate soil from the water reservoir. Is this necessary, and what fabric should be used?
Answer:
Most conventional wicking systems rely on a separate water container beneath the soil, which works for pots but is impractical for large areas. My system has no barrier. Water is stored directly within soil and organic material.
Normally, plants only access water between field capacity and wilting point, which is often about 10% of the soil volume. By extending storage from saturation down to wilting point, available water is increased several times, particularly with coarse organic material. While liquid water storage may hold more water per litre, soil-based systems can store vastly more water overall and scale to farm size.
I am currently linking multiple beds along contours so water can flow slowly across large areas. Although the system is patented, home growers are encouraged to use it freely.
Pollination in Shade Houses
Question:
If a shade house is used to exclude pests and birds, does it interfere with pollination?
Answer:
Commercial growers often pollinate by hand or keep beehives inside hot houses. In my experience, particularly in Queensland where insects are abundant, pollination has not been a problem.
Best Material for the Reservoir Layer
Question:
I have access to street mulch from tree loppers and well-composted sheep manure. Which is better for the organic matrix?
Answer:
Tree mulch is best for the reservoir layer, but some species, particularly pines, release growth inhibitors. Allow the mulch to weather while kept moist for several weeks so microbes can break down toxins. If growth later appears poor, the bed can be flushed.
As decomposition consumes nitrogen, composted manure is best mixed into the root zone rather than the reservoir layer.
Surface Wetness in Winter
Question:
In winter the soil surface stays wet. Am I adding too much water?
Answer:
Yes, most likely. The surface should appear dry most of the time. Constant surface moisture encourages mould. In winter, do not fill the reservoir to the overflow level. Experiment with lower fill levels and reduce watering frequency. Allow the lower zone to dry periodically; there is still ample water retained in the soil.
Managing water in wicking beds is about observation and adjustment. The system is forgiving, but it works best when water input matches plant demand and seasonal conditions.
