Evaluating peat-free propagation media suitable for production of high-quality ornamental transplants

Project Team

Dr Francis Rayns

Dr Margi Lennartsson-Turner

Victoria Adams

Dr Raghavendra Prasad (RHS)

Professor Alistair Griffiths (RHS)

Funder

Project overview

The PhD project aims to bridge the scientific and technical knowledge gap in peat-free plant production within the ornamental horticulture sector. Specifically, this PhD focuses on optimising propagation media formulations, irrigation and nutrition regimes. The research aims to advance cultivation protocols currently used, derived from evidence-based findings to support the transition to peat-free horticulture.

This initiative is part of an RHS-led research program that unites government bodies, growers, and growing media manufacturers to facilitate the horticultural industry’s shift away from peat-based practices based on scientific research. The research will be grounded in rigour to ensure the evidence-based findings support the viability and practicality of peat-free practices in horticultural industry application.

Find out more about the RHS Peat-Free Project: https://www.rhs.org.uk/science/transition-to-peat-free.

Historically peat has been the most widely used medium for plant propagation. Peat extraction for horticultural use releases stable, sequestered carbon into the active carbon cycle, exacerbating climate change. Therefore, transitioning to peat-free horticulture and finding growing media alternatives which are comparatively successful to peat is of great significance.

Producing high-quality young plant material is a challenging process which requires the successful implementation of various horticultural practices. The entire process must ensure the quick establishment of plants from seeds or cuttings, appropriate growth rates, and optimal root and shoot development, to produce high-quality young plants. Due to historic reliance on peat as a propagation medium there is a consequent lack of research on the characteristics and suitability of new-generation propagation materials, the transition to peat-free propagation remains a significant challenge for the UK horticulture industry. To facilitate the UK’s transition to 100% peat-free production scientific research is required to support young plant producers.

Project Objectives

1. Characterisation: Examine the physical, chemical, and biological properties of peat-free propagation/plug material to understand and establish their interactions.
2. Trial Propagation Media: Test peat-free growing media/plug materials suitable for ornamental young plant propagation.
3. Study Plant Response: Analyse the morphological, physiological, and biochemical responses of young peat-free plug plants.
4. Develop Regimes: Investigate optimal irrigation and nutrition regimes for peat-free plugs.
5. Role of Biological Agents: Understand the influence of biological agents on nutritional availability, growth, development, and quality of peat-free plug plants.
6. Influence of Additives: Investigate the influence of additives e.g. biological agents.

Impact Statement

The UK’s horticultural sector is under transition to phase out use of peat by 2026, with the technical exemption of propagation set for 2030 as per the proposed government legislation. This environmental initiative is part of the broader 25-Year UK Environment Plan, which also aims to restore degraded habitats including peatlands by 2030. Peatlands are the most carbon-dense terrestrial ecosystem on the planet, capable of storing carbon for 1000s of years representing up to 44% of all soil carbon, this exceeds the carbon stored in all other vegetation types including the world’s forests combined. Peat bogs are additionally important for biodiversity conservation, they are characterised by waterlogged, nutrient-poor conditions, and host a range of specialized species (flora and fauna) which are adapted to these environments, many of which are endemic or rare. Degraded peat bogs are major sources of carbon emissions and do not offer hydrological or conservation benefits. Hence it is essential to phase out the use of peat used for commercial horticulture purposes. There is a significant gap in research on peat-free propagation media within the ornamental horticulture sector, our current knowledge and technical understanding of peat-based materials are still in their infancy compared to peat-based media.