Trials by the Royal Horticultural Society (RHS) demonstrate that peat-free growing media can perform comparably or better than peat-based alternatives using the same amount of water. Following an RHS survey conducted amongst 400 growers in 2023, irrigation management proved to be the main concern and has hence been a key focus for RHS research to develop new growing media that avoid the need for extra irrigation. Peat-free media’s ‘dry on top’ appearance can sometimes prove misleading and lead to overwatering, but the RHS hope that these new findings may result in growers reviewing and optimising water use. Improved understanding of the unique water retention properties of the chosen peat-free growing media, water usage can be reduced without compromising plant quality.
According to the RHS, the latest trials were carried out with four growers from across the UK (covering alpines, ericaceous plants, shrubs and herbaceous perennials) and six growing media manufacturers. The trials were designed to evaluate factors including, understanding the irrigation and nutrition requirements of different peat-free mixes as well as the saleability of plants produced. Participating growers tested up to six peat-free mixes against a nursery peat-added control.
During the trials, the commercial growers maintained their usual irrigation practices without making any adjustments for the peat-free media. The results showed that when treated under standard nursery production conditions, some peat-free options outperformed the peat-based control when it came to water retention and use. In addition, nursery staff in all four nurseries considered some of the plants grown in peat-free mixes, to be more marketable than those grown in peat-reduced controls.
Dr Alistair Griffiths, RHS Director of Science, said: “These trials provide robust evidence that peat-free growing media are as water efficient as peat-based in spite of the preconceptions. This is an exciting development for the environmental horticulture industry, as it highlights progression towards accelerating the transition to peat free and improving water and nutrient management. These findings mark an important step towards more sustainable, peat-free practices across the sector.”
Improved water management also offers added benefits for nutrient retention. Addressing overwatering and leeching ensures nutrients remain available to plants longer, enhancing growth efficiency whilst reducing environmental impact. According to the charity, these findings reinforce the potential of peat-free growing media to support sustainable horticultural practices while meeting growers’ operational needs.
The RHS Peat-Free Fellowship, supported by Defra, is a collaboration with eight commercial growers (Allensmore Nurseries, Hillier Nurseries, Hills Plants, Johnsons Nurseries, The FarPlants Group, Lovania Nurseries, Vitacress and Volmary) and a range of professional growing media manufacturers catering to the ornamental horticulture industry. The growing media used in these trials are all commercially available at scale to the industry and sourced from Bulrush Horticulture, ICL, Jiffy, Klasmann Deilmann, Melcourt and Sinclair.
For reference, the full report from the trials is available to read on RHS Science.