Hope for a peat-free future

Riverford Organic Farmers use approximately 228 cubic metres of peat each year to grow seedlings in peat blocks. This equates to 38 tonnes of carbon (tCO₂e) being released into our atmosphere. The excavation of peat renders the landscape ineffective at sequestering carbon and degrades vital ecosystems. The list goes on… We are not proud of using this amount of peat. In our quest to go “beyond organic” and to push at the boundaries of sustainable farming, our use of peat is dragging us back.

Not all of our seedlings are grown in peat. We buy our seedlings from plant nurseries. Delfland Nurseries are 100 per cent peat-free in all seedlings that are grown in modules. Seedlings with strong root structures (e.g. broccoli) are grown in modules as their roots bind the growing medium together. The seedlings can be easily handled whilst they are being planted by our field team.

Crops such as lettuce, tomatoes and spring onions have finer root structures. The seedling is easily pulled away from its life supporting growing medium when handled. Additionally, their leaves are more delicate than leaves of crops such as broccoli. Their leaves are more vulnerable to damage during mechanical module planting. At our scale of growing, we would have a large level of crop loss if we were to grow these crops in modules. Therefore, we plant seedlings with finer root structures in blocks that are 80% peat. Blocks are self-supporting structures that are created when the growing medium is pushed together at a high force. The growing medium is cohesive, so it does not require a strong root structure to keep it together.

Seedlings growing in blocks at Delfland Nurseries.

Unfortunately, peat is a perfect medium for blocks. It is naturally cohesive, it holds an optimal volume of water and combination of nutrients to support seedling growth. We are still dependent on peat for some practices in horticulture despite decades passing since the peat-free movement begun. Therefore, in 2023 we embarked on an ambitious project that aims to find an effective peat-free blocking medium with Delfland Nurseries, the Coventry University and Cambridge Eco Ltd.

Putting our peat-free recipes to the test

In April, we published an update on our collaborative peat-free blocking project. The team at Coventry University had developed five peat-free blocking recipes for media that all went through the blocking machine at Delfland Nurseries. We have since taken two more batches of peat-free blocking media to Delfland Nurseries.

We aimed to answer three questions in these trials: 1) could the media make it through the blocking machine and be sown automatically, 2) could the seeds germinate (start growing) and 3) could the media supply the sufficient nutrients to support plant growth?

We compared the germination and growth rates of seedlings grown in our peat-free media to seedlings grown in peat.

Francis and Judith from Coventry University, carrying out assessments on lettuce prior to planting.

The development of the peat-free recipes was an iterative process. Ingredients and methods of processing the ingredients were changed in response to the findings of each trial. In trials one and two, we found that the peat-free blocking media stuck to the blocking machine, making it difficult to sow the seeds automatically. Lettuce did not grow in all peat-free recipes and growth rates were slower than plants sown in the normal blocks containing peat.

We did not expect to solve the issue straight away. The team hypothesised why the peat-free media stuck to the blocking machine and why they did not support plant growth. The team assessed which recipes performed the best to inform these hypotheses. Coventry University carried out experiments to test these hypotheses. For example, we found that the nutritional content of individual materials varied between batches of bulk materials.

We made great progress for the final trial thanks to these background experiments. We were able to reduce adhesion of the peat-free media to the blocking machine. We increased the proportion of plants that were able to germinate in the peat-free media although our peat-free blends resulted in slower growth than in the commercial peat formulation

Once the lettuces were large enough they were planted either in the field at Riverford or a polytunnel at Coventry University or Riverford. The results of our field trials were hopeful. All peat-free blocks were able to be planted by our tractor mounted planter. Before the project began, it was thought that the peat-free blocks would crumble when going through the planter. The lettuce was planted amongst the commercial crop of lettuce at Riverford. They were left to grow for the same number of weeks that the commercial lettuce was left to grow. The weights of each lettuce head were compared, and some peat-free recipes showed similar final yields to blocks containing peat.

We have been limited by time and resource so there are some caveats to our conclusions. We would ideally repeat our trials in different growing seasons, in different regions and with different crops. In the future we would want to trial our peat-free recipes on different farms, in different years and with different crops such as spring onions.

A sustainable recipe

Peat stores carbon. When peat is extracted, the carbon oxidises and becomes the greenhouse gas, carbon dioxide (CO₂). In one estimate, peat extracted for UK horticulture in 2020 amounted to 880,000 tonnes of CO2 (equivalent to 4,600 car journeys to and from the moon!). We could assume that the alternative materials that we have used in our peat-free recipes may have a much lower carbon footprint than peat. However, we want to be certain that the ingredients used in our peat-free recipes really are more sustainable than those used in the standard peat block.

We need to consider multiple criteria when assessing the sustainability of our peat-free recipes. For example, whilst some peat alternatives may have a lower carbon footprint than peat, they may have a higher water use footprint. In the final part of our project, our peat-free recipes will be evaluated in line with the Responsible Sourcing and Manufacture of Growing Media scheme which has recently been developed by the horticulture industry. In this evaluation, growing media ingredients are evaluated in relation to seven responsible sourcing criteria including: energy use, water use, social compliance, habitat & biodiversity, pollution, resource use efficiency and renewability.

Affordability and peat

Our dependence on peat mirrors our dependence on fossil fuels. It will be better to leave it in the ground, yet our system relies upon its extraction. Our society has externalised the costs of its extraction and use so that citizens bear the long-term burden of climate change and biodiversity loss. As with many products that are more sustainable, the citizen pays the premium from their own purse. We are wary that the sourcing and the processing of our peat-free recipes will cost more than the production costs of blocks containing peat. We have kept this in mind when considering materials for the recipes, considering materials of low value such as waste materials. We’ll now start to evaluate our peat-free recipes in terms of affordability (i.e. will the production cost of a lettuce increase?).

Two years to create a peat-free blocking medium

Growing media manufacturers have told us that it usually takes a minimum of five years for a new growing medium to be developed for commercial production and our project only has funding for two years. We are now three quarters of the way through and we feel that we have gained a wealth of knowledge. We have shown that it is feasible to create peat-free blocking medium from UK sources. We have recipes for peat-free blocking medium that show comparable yields to blocking media that contains peat. We are going to meet the objectives of this project after carrying out the sustainability and economic analyses. However, Delfland Nurseries and Riverford Organic Farmers will not be able to grow seedlings in peat-free blocks as no one is yet producing the new formulations at a commercial scale.

We are now seeking funding for phase two of this project which will have the aim of scaling up production of our recipes. This project will fine-tune the recipe so, for example, there is less variability between batches of materials. This project will need to deal with sourcing the material in large quantities and will need to create an efficient production process.

Hope for a peat-free future

We were aware that there was looming legislation to ban peat sales to professional growers by 2030 when we started this project. This ban remains to be written into legislation as we are finishing this project. On 7^th November, Sarah Dyke, a liberal democrat MP for Glastonbury and Somerton introduced the Horticultural Peat (Prohibition of Sale) Bill to parliament for the second time. The bill is now awaiting its second reading on 24^th January 2025. We initially entered into this project as we know that removing peat from our seedling production is the right thing to do as a responsible business. The peat-free movement started approximately 40 years ago. The question remains, will it take another 40 years for the horticulture industry to become peat-free when legislation is looming but not in law?