New published paper: Why “sustainable growing media” is used incorrectly, and what needs to be done about it
- May 18
- 6 min read
“Sustainable growing media” is a commonly used phrase in horticulture, environmental policy and industry communications. It is also one of the least defined.
A new scientific paper in Frontiers in Horticulture, co-led by Growing Media Europe's Dr Alexander Sentinella with Dr Siv Mari Aurdal (NIBIO, Norway) and Professor Beatrix Alsanius (SLU, Sweden) with six other international authors, argues that the term is being applied so loosely that it now risks misleading the very people who depend on it: growers, regulators, and policymakers shaping the rules for a more sustainable horticultural sector.[1]
The paper is direct about the problem: The paper is direct about the problem:
“Materials are frequently characterised as sustainable based on single attributes, such as being peat-free, recycled, renewable or aligned with policy priorities, without demonstrating reliable horticultural performance, economic viability, social responsibility or reduced environmental impact within real production systems.”
In other words, the label of “sustainable” has been doing the work that evidence should be doing.
What growing media are, and why this matters
Growing media (also called potting soils or substrates) are the materials in which plants or mushrooms are grown when they are not grown directly in field soil. They support nursery plants, ornamentals, soft fruit, salads, herbs, mushrooms, and most of what is produced in greenhouses or containers across Europe.[2] Their function is to manage water, air and nutrients around plant roots, reliably and at scale.
Because growing media sit at the start of a long value chain, decisions about what they are made of ripple outwards. They affect carbon footprints, supply chain resilience, grower economics, food and ornamental plant prices, and the credibility of sustainability claims downstream. This is why we define “sustainable” matters far beyond the growing medium itself.
Sustainability is not a property of a material
The core argument of the paper is straightforward. Sustainability is not something a material has. It is an outcome of a system. It depends on which crop is being grown, at what scale, in which production system, with what supply chain, and against which trade-offs.
Calling a material sustainable simply because it is not peat, renewable, or recycled, without evidence of what it actually does in practice, is not a scientific claim. It is, at best, an aspiration. The authors are clear:
“The difficulty of defining “sustainable growing media” lies less in the absence of suitable materials than in the tendency to treat sustainability as an intrinsic attribute rather than a conditional outcome.”
This is a significant reframing for policy. It means that a substrate cannot, on its own, be declared sustainable. What can be declared sustainable, or more sustainable, is a specific use of a specific material in a specific production context, with evidence to support the claim.
All three pillars of sustainability must be considered together
Sustainability can be defined across three pillars: environmental, economic and social. The paper shows that in growing media, each of these is routinely treated in isolation, or simply ignored.
Environmental claims dominate, but often without measurement
Peat is frequently labelled environmentally unsustainable using global peatland statistics that do not reflect actual extraction practices, regional contexts or what would replace it.[3] Other growing media constituents are labelled sustainable because they are non-peat, without measuring their processing emissions, transport impacts or performance in real crops.[4]
Economic sustainability is critical, but is usually reduced to price
The paper sets out that economic sustainability has to be considered at three levels: manufacturing (raw material costs, scalability, logistics), use (crop performance, yield stability, input efficiency), and reuse or refurbishment (sterilisation, quality retention, handling). A growing medium that increases production risk or requires growers to compensate with extra fertiliser, water or labour undermines the very system it is meant to support, however well-intentioned its environmental story.
Social sustainability is the least developed pillar
It covers labour conditions, occupational health and safety, community impacts and supply chain transparency. As more recycled and side-stream organic materials are used in growing media, risks such as pathogenic contamination from inadequately composted inputs become more relevant, not less. Social Life Cycle Assessment (S-LCA) offers a framework to evaluate these dimensions, but the available data is still patchy.
Why this matters for policymakers in particular
Horticulture is a low-margin sector with limited tolerance for production risk. A growing medium that underperforms, however well-intentioned, undermines the system it is meant to support and can push environmental, economic and social burdens elsewhere rather than reduce them.
The paper is explicit about the policy implication:
“For policy, the findings help explain why proxy-based targets can support transition objectives but cannot be conflated with sustainability outcomes at the growing media or production system level.”
This is an important distinction. A simple proxy such as “peat-free by year X” can be a useful policy lever for steering a transition. But it is not a measure of whether outcomes have improved. Without evidence on performance, economics and social conditions, a proxy target can shift environmental burdens, introduce new biosecurity risks, or simply be unaffordable for growers to meet.
The honest answer for policy is not to abandon the concept of sustainable growing media. It is to use it more precisely.
Eight conditions for using the term responsibly
Rather than proposing a new definition, or abandoning the concept, the authors set out eight minimum conditions for using “sustainable growing media” responsibly:
1. Consider all three pillars (environmental, economic, social) explicitly.
2. Specify which pillar(s) a claim is actually addressing.
3. Frame sustainability at the system level, not the material level.
4. Measure impacts rather than infer them from material categories such as peat-free, renewable, recycled or bio.
5. Demonstrate functional and economic performance for the intended use.
6. Make trade-offs and uncertainties explicit.
7. Avoid absolute or binary claims such as “sustainable” or “unsustainable” without qualification. Instead use language such as “more sustainable in terms of climate impact”.
8. Where comprehensive assessment is not available, use precise descriptors (for example “responsibly sourced”, “quantified carbon footprint under stated assumptions”, or “demonstrated reuse potential”) instead of blanket sustainability claims.
As the authors themselves put it:
“These conditions are intentionally modest. They do not require comprehensive assessment in all cases, but they do require transparency, explicit scope, and proportional evidence.”
This is a workable standard. It does not demand a full Life Cycle Assessment for every product or every claim. It demands that claims be honest about what they cover and what they do not.
Where the field needs to go
The paper closes by setting out the direction of travel. Future progress depends less on redefining sustainability and more on improving how evidence is generated and communicated. Three areas are highlighted: integrating functional performance with environmental and economic assessment, improving transparency around processing and supply chain impacts, and developing approaches that capture risk, uncertainty and distributional effects across the value chain.
The closing line is one we would underline for any policymaker working in this space:
“Sustainability in growing media should be treated as an evolving, system-level outcome that must be demonstrated within a defined production system rather than a fixed label.”
For Growing Media Europe, we do not see this is a critical position. It is a constructive one. The growing media sector is investing significantly in better data, in Life Cycle Assessment methodologies, and in industry-wide frameworks such as the Growing Media Environmental Footprint Guideline.[5] What the sector now needs from research and policy is the same rigour applied to sustainability language: claims grounded in evidence, scoped clearly, and honest about what they include.
That is how sustainability in growing media moves from a contested label to a credible, useful basis for decisions.
For media enquiries, contact the GME Science Coordinator alex.sentinella@growing-media.eu
[1]Aurdal, S. M., Sentinella, A. T., Schmilewski, G., Altland, J., Caron, J., Alexander, P., Holtkamp, M., Vandecasteele, B., & Alsanius, B. (2026). The challenge of defining "sustainable growing media": Why the term is used incorrectly and what needs to be done about it. Frontiers in Horticulture, 5, 1800902. https://doi.org/10.3389/fhort.2026.1800902 All quotations in this summary are from this paper.
[2]Technical definition used in the paper, following Caron, J., Schmilewski, G., Alsanius, B. W., Zheng, Y., & Michel, J. C. (2023), Acta Horticulturae, and Regulation (EU) 2019/1009 (Fertilising Products Regulation).
[3]Barrett, G. E., Alexander, P. D., Robinson, J. S., & Bragg, N. C. (2016). Achieving environmentally sustainable growing media for soilless plant cultivation systems – A review. Scientia Horticulturae, 212, 220–234. Cited in the paper.
[4]See for example Goglio, P., et al. (2025), Science of the Total Environment, 964, 178624; and Hirschler, O., & Thrän, D. (2023), Horticulturae, 9, 919. Both are cited in the paper.
[5]Growing Media Environmental Footprint Guideline (GMEF), Growing Media Europe (2024), Currently Version 2.0. See www.growing-media.eu/lcaguidelines
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