Scientists from the RHS have successfully grown two popular varieties of carnivorous pitcher plants in five different peat-free growing media, all judged to be superior to the control plants grown in 100% peat.
Carnivorous plants were believed to be one of the most difficult plant groups to grow peat-free as many are found growing in peatland habitats naturally.
The RHS, committed to be 100% peat free by the end of 2025 and to helping the horticulture industry transition away from the use of peat, took on the challenge of growing these specialist plants in alternative materials. RHS scientists, led by Dr Marc Redmile-Gordon, worked with Sean Higgs of Floralive, a carnivorous plant nursery that has grown peat-free since 1990, to demonstrate that high-quality pitcher plants could be successfully grown without peat and to highlight some of the most promising options for peat-free growing media.
Sarracenia plants established from peat-free propagules were grown under identical conditions in six different growing media combinations, including mixes of sustainably-grown sphagnum moss, pine bark and acidified biochar, commercially formulated peat-free media produced by Floralive and a control group grown in peat.
Judges, including carnivorous plant experts Roy Cheek (also a judge at the RHS Chelsea Flower Show) and Mike King, national collection holder for Sarracenias, scored the plants based on their growth and aspects of their appearance (including size, uniformity, colour and attractiveness).
Plants grown in blends of sphagnum and other organic materials were all judged to be vastly superior to those grown in peat, with different peat-free media performing best for each of the two cultivars. In particular, the addition of pine bark benefitted the S. leucophylla hybrid. Roy Cheek was especially impressed by the array of colours on display in the Sarracenia grown without peat.
Professor Alistair Griffiths, RHS Director of Science, said:
“This research is a positive step forwards in delivering the RHS Sustainability Climate Positive Target and in the RHS transitioning to peat free by the end of 2025. It is very exciting to see the results from the judging clearly demonstrating that the plants grown in peat were inferior to those grown in alternatives, and that Sarracenia can be grown to the highest standard without peat. Moving away from peat in horticulture has a key role in meeting net zero through protecting and restoring peatlands, turning them from carbon sources to carbon sinks and preventing further loss of these vital habitats. Our research comes at a critical point in the UK’s response to the climate crisis, when it is more important than ever that all possible reductions in emissions are made.”
Following the success of the Sarracenia experiment, the team will now look at growing other popular carnivorous plants without peat, including Venus flytraps (Dionaea muscipula), as well as testing a wider range of ingredient mixes and growing protocols to aid the UK horticulture industry in transitioning profitably away from peat.