Coir Substrate Recycling Results

Tasmanian hydroponic strawberry growers are weighing up three substrate choices: fresh coir, second-year reuse, or coir mixes.

Commercial trials coordinated by Fruit Growers Tasmania with RMCG have put evidence around how these three substrate options perform on-farm. 

Results suggest yield losses in reused coir are driven mainly by physical breakdown and wet, low-oxygen zones rather than simple disease risk.

Below we summarise the key findings: why reused coir tends to lose performance, what the economic analysis says under today’s assumptions, and how to trial coir mixes safely, including practical steps to manage risk and adjust irrigation and fertigation.

The project also includes an economic model and practical guidance for low-risk on-farm mix trials.

Why second year reused coir loses performance

Across the commercial trials, the consistent pattern was that second-year coir tended to lose performance mainly due to physical breakdown of the substrate, rather than a simple increase in disease risk.

As coir ages through a season, fine particles migrate down through the profile and gradually block pore spaces in the lower root zone. Drainage slows, the base of the bag or trough stays wetter for longer, and parts of the profile shift toward anaerobic conditions. Once that happens, root function declines and plants become harder to manage later in the season.

In practice, this shows up as more variable moisture behaviour and a narrowing management window. Growers can find the top of the profile looking acceptable while the bottom remains saturated, particularly in areas that are difficult to flush. In trough systems, corners and low points are especially prone to staying wet, and flushing fertiliser salts can be less effective. Over time, this contributes to localised EC build-up and additional plant stress, even when the fertigation recipe hasn’t changed.

Pathogen testing in the project did detect organisms in some reused treatments, but overall, the evidence points to structure and water management as the primary drivers of the yield penalty seen in straight second-year coir.

In practical terms, extending substrate life is less about intensive disinfection and more about maintaining porosity and drainage. That’s why the better-performing approaches in the trials were those that improved the physical profile, either by blending with more structurally stable material or by paying close attention to container design and flushing behaviour.

Read the final report

What the economics say

The economic analysis attached to the project supports what many growers already suspected: under current assumptions, the 'status quo' system of fresh coir in bags for a single season still tends to deliver the strongest gross margin. That result is driven by yield stability and management familiarity. Even when reused or mixed substrates reduce input costs, a meaningful yield penalty can quickly erode those savings if the system is not managed carefully.

However, the modelling also makes an important point: the advantage of fresh coir is not as secure as it first appears. When the numbers are stress-tested, small shifts in key variables can narrow the gap or even change the ranking. If coir prices rise, the relative attractiveness of lower-cost reuse options improves quickly. Conversely, when fruit prices are strong, the yield stability of fresh coir becomes more valuable, and the status quo tends to pull ahead.

In other words, reuse and mixed substrates shouldn’t be read as a universal replacement for fresh coir today, but they do represent a meaningful hedge against future scenarios such as increased input pricing, freight disruption, or changing waste costs.

The other key takeaway is that 'profitability' isn’t a single number that can be lifted from a report and applied to every farm. Labour assumptions, disposal costs, tunnel layout, irrigation infrastructure and market timing can all influence the outcome, and some costs are difficult to quantify consistently across businesses.

Alongside the modelling, an Excel tool is available to help growers stress-test the results against their own assumptions (fruit price, coir cost, yields and major inputs). It’s designed to support decisions, not replace them.

Download: Coir substrate economic calculator (Excel)

If you want to trial coir mixes: how to do it safely

If you want to trial coir mixes on-farm, the strongest message from this project is to treat it as a controlled change, not a straight swap.

• Start small, run it side-by-side with your current fresh coir system, and set it up so you’re learning something useful even if the result is “not yet”.
  A simple approach is to allocate a few bays (or a defined number of tables) to a single mix and keep everything else as your farm standard. That gives you a meaningful comparison without putting your season at risk.
• Plan for early-season fruit management.
  Mixed substrates and trough systems can increase the chance of early fruit sitting on damp substrate surfaces, which can translate into avoidable losses. Topper mats are a practical, low-cost control that can help separate fruit from the substrate surface during establishment and early pick, and they’re worth considering as part of any mix trial so you’re not judging the substrate on preventable fruit loss.
• Expect that irrigation and fertigation may need adjustment.
  The whole point of mixing is to change the physical profile, including drainage, water-holding and air-filled porosity, so the “right” irrigation strategy will likely shift as well.
• Define in advance what you’ll monitor (at a minimum: drainage behaviour, EC trends in hard-to-flush zones, and plant response through warm periods) and keep notes on changes you make.
  The goal isn’t perfection in year one; it’s building a farm-specific playbook for how that mix behaves under your conditions.

Be clear about what success looks like before you start. Yield matters, but so do fruit quality, labour costs and waste outcomes.

If your end goal includes an off-farm pathway for spent substrate, plan for contamination control from day one. Plastic fragments can be introduced as bags are handled, cut or removed, and downstream reuse or processing options may depend on how clean the material is.

Bottom line

• There is no single 'best' substrate choice for every farm.
• Second-year coir tended to lose performance mainly due to physical breakdown and wetter, low-oxygen zones in the lower profile.
• Under current assumptions, fresh coir remains the most reliable benchmark, but rankings can shift with coir price and fruit price.
• Coir mixes can work, but treat them as a controlled  incremental change: start small, monitor drainage and EC, and expect irrigation/fertigation adjustments.
• Done well, mixes become a practical hedge against input costs, freight risk and waste pressures.
• Download the calculator to test scenarios using your own assumptions.

 

This project has been supported by the Tasmanian Government through the Agricultural Development Fund.