Vegetable Propagation: Grower-led peat reduction & replacement demonstration trials 2021

Ending peat use remains high on the UK Government’s agenda. The goal is for all amateur and professional uses of peat to end by 2030. In May 2021, the Government published its Peat Action Plan, in which they declare a consultation in 2021, to examine the feasibility of a number of measures to end the use of peat in horticultural plant production.

Peat is also becoming a hard commodity to source. With this comes price increases which have already been confirmed by a large UK plant propagator. The cost of peat currently makes 40–50% of vegetable plant propagation production costs when in abundance; costs will rise as peat becomes scarce. Peat availability issues are partly a result of new Republic of Ireland (ROI) rules on the extraction of peat from bogs greater than 30 ha, which now require companies to go through a licensing and planning regime, and the fact that Bord na Mona no longer have plans to harvest peat. Most of the peat that is used in commercial horticulture in the UK comes from the ROI.

From January 2015 to December 2019, Defra, AHDB, and the peat manufacturing and users’ industry funded a £1 million project, CP 138, entitled ‘Transition to responsibly sourced growing media use within UK horticulture’. The ADAS-led project delivered a model for predicting the performance of responsibly sourced growing media (RSGM) blends based on coir, bark, wood fibre and green compost. The model uses three physical properties that were identified as crucial in describing the functionally of media: air-filled porosity, available water and bulk density.

Peat-free blends and reduced peat blends were produced, and their performances evaluated for different crops in CP 138. Some horticultural sectors such as trees and hedging production have made significant strides towards using reduced peat and peat-free growing media. This is not the case in vegetable plant propagation, as challenges which include the need for alternative media to have ‘stickiness’, a property found in certain types of peat, are still to be resolved. Stickiness is a critical attribute that is necessary for block production in lettuce and celery propagation.  Work has also demonstrated challenges in propagating uniform brassica transplants on alternative media in modules; this has not been an issue where peat is used. 

Suitable peat-free RSGM blends were produced for the trials by ADAS for pot-herb production and for brassica propagation. For lettuce, reduced peat blends were used, as peat-free blends were difficult to use in blocking. Brassica and lettuce plants raised on the trial blends were rated as ‘good’ by vegetable plant propagators at an AHDB event held in 2018. Block-raised lettuce was planted on, monitored and assessed through to harvest, but module raised brassicas were not, when the event was held. However, following the event, brassicas were grown on at the Elsoms’ trials grounds, but there were issues with plant establishment and bird damage resulting in a lack of useful outcomes.

Following a request from the Plant Propagators Ltd technical committee, AHDB published a call to potential contractors, advertising the opportunity to work on a grower-led demonstration project looking at reduced peat and peat-free blends for commercial brassica, lettuce and celery propagation. ADAS Horticulture were awarded the seven-month project, which started in April and ends in November 2021. Dr Barry MulHolland, Dr Andrew Watson and Chloe Whiteside of ADAS are working on this project.

1. Source emerging commercial growing media that can be used for comparative trials with existing nursery products
2. Source raw materials (growing media and binding agents) for suitability testing and for creating model blends that can be used in plant propagation
3. Ensure that new commercial products or blends created are compatible with vegetable propagation mechanisation (brassica module propagation; lettuce and celery blocking and a new commercial propagation system called Ellepot)
4. Assess the performance of plants that are raised on commercial media and new blends at key production stages during propagation, at planting and growing on of plants in the field
5. Interact and communicate with growers at each stage of the testing and development cycle
6. Report findings and highlight developments that are suitable for immediate uptake by growers or identify areas of progress and future work needs to assist the industry in moving to peat-free plant raising