Peat has long been the favourite growing media for commercial and domestic horticulture thanks to its stable structure, ability to hold onto nutrients and water, and plentiful availability. This makes finding an alternative, particularly in controlled environment agriculture (CEA), a major challenge for the sector.
And while finding a growing media that matches peat’s desirable profile has been the focus of research for more than 20 years, the conclusion seems to be there is no silver bullet in replacing the UK’s need for three million m3 of media a year to feed the professional and retail markets.
Significant barriers exist due to challenges in securing enough good quality alternatives at an economical price, and while there are products that will do for now, a longer-term strategy is needed.
The adoption of peat-free alternatives by growers will highly depend on their technical, financial and infrastructure limitations says independent agronomist Claire Donkin, who has been exploring peat-alternatives for much of her career.
“As a broad brushstroke the more automated the production system is, the more challenging the adoption of peat-free alternatives will be. Plant propagation, glasshouse or CEA systems have been, in most cases designed and developed around the structural properties of peat. And what we don’t have is a peat replacement that is exactly the same, so there is an inherent limitation around the existing growing infrastructure.
“If you have a consistent substrate like peat, you can plan your irrigation schedule for example, because you know what its water holding capacity is and how long it’ll support that plant for before you have to irrigate it again. It is quite a difficult adaption to make.”
Coir, a byproduct of coconut processing has emerged as probably the close comparator to peat and is increasingly favoured for its lightweight nature and effective water retention.
However, there’s a risk it could follow the same unfortunate fate as peat, as it faces its own environmental challenges. This is because it has to be aged and washed several times in fresh water and treated with calcium nitrate to avoid the release of phytotoxic levels of sodium and potassium during use. It also has to be sourced and transported by ship over long distances before being further shipped within the UK on lorries, so has high carbon miles.
Some growers are also concerned about the longer-term supply of coir if demand for it increases globally. The use of coir fell in 2021 due to supply chain issues in India and Sri Lanka related to Covid but availability is increasing again, and coir now accounts for the largest volume of non-peat material in the professional horticulture sector.
Ben Tea, glasshouse manager and technical grower for NIAB, who has been conducting growing media trials for several years, says there are already some commercial herb growers trialling peat- and coir-free alternatives.
“That will be the future,” he says.
Artificial alternatives, including vermiculite and perlite which are sterile, naturally occurring minerals with high water absorption can be blended with other substrates including wood fibre and bark-based substrates.
“These materials can provide adequate water retention and properties for good plant growth,” says Ben. “However, one wood fibre, and another are not the same. They have different particle sizes, and there will be differences in their degradation depending on how long they have been processed.
“Woodfibre like other organic material needs to undergo decomposition to process the carbon so in a media mix the microorganisms will then take up nitrogen which is meant for the plant, and starve the plant. Coir produces a lot of potassium as it breaks down and bark has high levels of manganese, so these wood byproducts can be very difficult to use and you have to get them right.”
Wood byproducts also face the same availability challenges as coir, because they are widely used across many industries, including the energy industry which is heavily subsidised by government.
Ben says: “The problem we have is availability of different materials as an industry. We buy in from the likes of South Asia, Canada, Germany and the Balkans because we do not have massive UK resources. If the EU decided overnight to become peat free, there would be significant strain on resources. We’re okay at present but in 10-15 years we could see real supply chain issues if material, such as coir suffered the same fate as peat.”
Materials that are in abundance like green and brown waste, compost or digestate are rarely used in commercial growing because they can contain high levels of herbicide residues, as well as bring up food safety issues caused by microbes.
Ben says: “The majority of the industry needs a growing media that has quite a low pH, and peat did that. Unfortunately, most other ingredients available in the amounts we need have high pH meaning we need to re-evaluate how we prepare them and how we fertilise them as the traditional methods aren’t appropriate anymore. We also have to address water holding issues which can lead to us adding manmade wetters and surfactants to achieve what peat could do naturally.
“However, there is lots of research being done and some good peat-free products out there, and we have time to make changes. Knowledge exchange and training are now extremely important – this generation of growers and professionals have the least support and the hardest job.”
Why is peat being banned in the UK?
Defra first announced a ban on peat use in both commercial and domestic horticulture in 2022, after it decided the industry had been too slow to react to a voluntary phase-out.
This was to prevent further loss of peatland habitats and to restore more peatland landscapes to their natural state, as the UK’s largest terrestrial carbon store. Defra believes by imposing this ban, it can restore 25,000 hectares of England’s peatland.
The government proposed a phased approach to the ban, beginning with bagged compost retail sales in 2025, followed by a ban on the professional use of peat in 2026. There are some exceptions, such as plant production methods where peat cannot be readily replaced, but by 2030 all uses of peat will be banned, says Defra.