Peat-free carnivores voted best in RHS trials by The Carnivorous Plant Society
“A turning point”: leading UK growers judge quality of peat-free Sarracenia to far exceed peat-grown plants, with news on supply and longevity of winning peat-free media
On Saturday 12 October, 43 members of The Carnivorous Plant Society, the UK charity dedicated to the study and conservation of carnivorous plants, visited RHS Wisley to hear updates from the RHS Transition to Peat-Free project and to view the exhibited Sarracenia and Venus flytraps of the ongoing Peat-Free Carnivores project.
The trials began in 2022, with the aim of researching successful, more sustainable alternatives to peat for the UK’s community of amateur and commercial carnivorous growers. Led by RHS Senior Soil Scientist Dr Marc Redmile-Gordon with materials support from peat-free supplier Floralive, the project strives to arm growers with the knowledge and availability of materials that will allow everyone to continue enjoying high-quality carnivorous plants peat-free.
Introducing the event, Professor Alistair Griffiths, RHS Director of Science & Collections, says: “Peatlands store over twice as much carbon as all the world’s forests combined, and store it for thousands of years. We need to stop every kilogram of carbon that we can. We can still grow amazing carnivorous plants – we just need to look at different aspects.”
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S. rosea and S. ‘Bella’ on trial
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Trials lead Marc Redmile-Gordon
A vote of confidence in peat-free carnivores
The Sarracenia trial, which has now completed its second year, is investigating the growth of two varieties of pitcher plant – Sarracenia rosea and Sarracenia ‘Bella’ – in 12 different growing media, including a peat control. When the trial began, there were only six different media being compared, but owing to exceptionally high survival and growth rates, six new potting mixes were included in 2023 for comparison.S. rosea and S. ‘Bella’ on trial
Trials lead Marc Redmile-Gordon
The runner-up medium for both plants was a mix of 75% sphagnum, 20% pine
Marc explains the use of a carnivorous-plant-specific biochar in the mix: “The main reasons for going peat-free are because slowing down carbon emissions for thousands of years has ongoing benefits for biodiversity. Perlite takes a lot of energy to manufacture, and while biochar shares many similarities with perlite (lightweight, porous, does not decompose), its carbon credentials are in stark contrast: instead of driving climate change like perlite, biochar can sequester carbon for millennia.”
Marc cautions against using “general purpose biochar, which can kill carnivorous plants”, emphasising the importance of only buying growing media mixes and components from trusted growers of carnivorous plants who can make a proper assessment of material quality.
The winning batches of S. rosea and S. ‘Bella’ grown in pure milled sphagnum
© Marc Redmile-Gordon![]()
© Marc Redmile-Gordon![]()
Progress for Venus flytraps
Marc extended his RHS peat-free trials programme to Venus flytraps in 2023. These were also displayed during the visit by The Carnivorous Plant Society.
Speaking at the event, Marc says: “We listened to you and included perlite in the peat control for Venus flytraps. Besides sphagnum again growing the best plants, the media that failed have revealed some important things about choosing a growing medium – if it smells bad, it is bad.
“Peat comes from an anaerobic system, and it makes an anaerobic system. Left in the bog, peat decomposes very slowly, but in wet pots it accelerates climate change. When we smell eggy emissions coming from peat, we know we are also driving climate change through emissions of methane and nitrous oxides,” says Marc. Agreeing with Marc, Matt Soper comments that this is especially the case when
An unexpected lead
During the viewing, Marc reveals a “rescue medium” he had used to propagate excess micropropagation material from the Venus flytrap investigation. These surplus plants, which are not part of the trial, are showing promise so far.
“This medium is sphagnum-based, but among other things, contains a mixture of grit and cork – grit is ideal as it does not decompose, and the cork helps to lighten the mix. This seems to be a path forwards for those who would prefer a reduced sphagnum mix, and my next project is to systematically test variations in proportions of the key components.”
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The Venus flytrap trial after one year
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Venus flytraps in rescue mix (not in trial)
Nursery success for sustainably farmed sphagnum
The Venus flytrap trial after one year
Venus flytraps in rescue mix (not in trial)
Matt Soper, owner of Hampshire Carnivorous Plants, is now also growing Sarracenia peat-free and is also trialling Drosera. He reports that milled farmed sphagnum has been the best peat alternative for him by far. “Milled sphagnum is a fantastic product,” he says. “What it’s going to come down to is how much can be supplied.”
Sphagnum comes in different grades as a growing medium, with the main formats being finely milled and coarsely chopped. “Milled is best for propagation, while coarser forms are better for potting on, since these are easier to handle and have a lower carbon footprint,” explains Marc.
Director of Science and Collections Alistair Griffiths has shared that the RHS is working with commercial partners with the aim of ensuring that the supply and distribution of British sustainably farmed sphagnum will be sufficient to meet the demands of the carnivorous growing market in the UK in the near future.
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© Olivia Drake![]()
Concerns addressed
Paul Richards, Assistant Conservation Officer at the Carnivorous Plant Society, says: “Price of sphagnum has been a concern, so it interests me that progress is being made with sustainable farming of sphagnum within the UK.”
Chair Ian Ladd says: “Water control in sphagnum can be complex for beginners – it can hold too much water in winter – and since fresh sphagnum grows, it needs an occasional trim if you’re using the long-fibre form so that it doesn’t strangle the roots of Venus flytraps. But it’s definitely the way to go.”
Marc adds that farmed sphagnum is supplied in dried form and he has not witnessed any regrowth, so he feels there is no need for concern over strangulation or competition in this case.
“Understanding of the growing media is key to water control,” says Sean Higgs. “Sphagnum won’t dry out as easily as some other media, so stop watering earlier on in autumn than you’re used to. My sphagnum had its last watering in early October – my other mixes will have their last watering at the end of October.
Matt Soper raised concerns about the longevity of sphagnum and peat-free media. Marc reassured growers with examples of S. rosea grown in a 75% sphagnum, 25% pine bark blend that had not been potted on in more than two years (pictured below), and pointed to no visible loss of volume or integrity.
Sarracenia rosea that have been growing in the same sphagnum/pine bark (75/25) mix for over two years without repotting
Medium still holding together firmly, with no appreciable loss of material over more than two years
Sean Higgs added greater assurance by displaying two plants that have each been growing in his peat-free mix for 10 and 27 years – with no need for any growing media replacement.
27-year-old Sarracenia and 10-year-old Darlingtonia grown peat-free by Sean Higgs
Closeup of Sean’s 27-year-old peat-free Sarracenia
“I use a 50/50 mix of sphagnum and cork granules,” says Matt. “The cork works and is recommended. It is currently more expensive than perlite, so it would be good to see a Government incentive to use it by levelling the prices up a bit in the interests of sustainability. We want to help the environment.”
An opportunity for UK horticulture
As is the case for many plant groups, carnivorous plugs grown on the Continent often still contain peat and may continue to after the ban in the UK, at which point we will be unable to import peat-based plugs. This could lead to either a movement towards peat-free plug production by major exporters such as The Netherlands, or an increased need for carnivorous propagation within the UK.
“Perhaps, with growers and suppliers across the industry struggling with changes in plant health regulations during import and potential future uncertainties around the peat status of European plugs, there could be no better time to bring more propagation in-house with support from industry and the Government,” says RHS peat-free research fellow Dr Raghavendra Prasad, who is running separate trials at eight leading UK nurseries to refine peat-free production of plugs, young plants and finished perennials, shrubs, culinary herbs, ericaceous and more.
“We already have some great materials for propagation in the UK,” says Alistair Griffiths. “This is an opportunity for British horticulture – we don’t need to rely on imports for carnivorous plants. Why can’t we do more propagation and plug production in the UK?”
Matt Soper agrees: “It would be a massive opportunity for UK horticulture and the whole industry if we had the facilities. We need Government investment in micropropagation labs in the UK.”
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Working together to find solutions
Addressing The Carnivorous Plant Society, Alistair says: “We at the RHS have been working really hard to find solutions, but to make these materials commercially available to you in quantity, we need your help. It is all about supply and demand.”
“It has been a really encouraging day,” says Alistair. “I feel we’re very close to carnivorous plants becoming peat-free in the UK.”
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Peat-free Venus flytraps exhibited on the day
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What next?
Peat-free Venus flytraps exhibited on the day
“We are working with the supply chain to make the materials we have been working with available for distribution in the very near future in the quantities required by the UK’s carnivorous growing sector,” says Alistair. “Watch this space.”
This is news that will be welcomed by carnivorous growers across the UK, as we prepare for the introduction of peat legislation to protect biodiversity and combat climate change.
“Sustainable supply of sphagnum associated with acceptable prices hasn’t been apparent until recently,” says Sean Higgs of Floralive. “The fact that a sustainable producer is going to be able to supply the volumes needed brings optimism for everyone.”
The trials team: Alistair Griffiths, Sean Higgs and Marc Redmile-Gordon
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