Strawberries Thrive in Second-Hand Substrate: The Case for Coir Recycling

Over the past few decades, there has been a significant shift from soil to soilless media in UK strawberry and raspberry production. With the phasing out of peat, coconut fibre (coir) has become the preferred substrate. Compared to field soils, coir enables growers to achieve consistently higher yields.

However, rising demand for coir, limited availability, and volatile shipping costs have increased production expenses for growers. The carbon footprint associated with importing substrate from Asia is also a concern, while further labour costs are incurred in replacing and disposing of waste coir.

As a result, the industry has come under growing pressure to find ways to extend the lifespan of coir. So far, growers have been hesitant to use it for more than a few cropping seasons due to concerns about the build-up of pests, diseases, and weeds, which reduce both yields and fruit quality. NIAB has been working with Overland Ltd to explore the potential for reusing coir substrate from strawberry crops.

Initial work was carried out through an EU-funded Interreg project, Horti-blue C, where coir bags used for strawberry production were directly replanted by removing the original plants and placing new plants into the same planting holes. It was found that where the coir was free of pathogens, June-bearing varieties tolerated replanting well, with little impact on yield.

However, everbearing varieties performed less successfully, showing a yield decline of 6–7% year on year. This is thought to be due to a reduction in air-filled porosity (AFP) and changes to the chemical and microbial properties of the coir as it ages.

Overland has since developed an automated system for recycling coir from strawberry bags. This includes low-labour, automated removal of bags from tunnels, followed by the extraction of plastic, leaves, roots, and crowns, leaving clean coir behind.

The coir is then treated in various ways before being made available for growers. Overland funded NIAB to conduct further research to evaluate how repeated cycles of growing and recycling alter coir properties over time. It was found that water-holding capacity increases while AFP decreases in recycled coir compared with virgin material. The extent of this change varied between coir manufacturers. Further changes were observed in pH, electrical conductivity, and nutrient content.

Automated, low-labour removal of bags from the tunnels

Interestingly, levels of crown rot (Phytophthora cactorum) tend to increase in directly reused and composted coir compared with virgin coir, though this has not been observed in Overland’s fully recycled product.

Growing Kent & Medway input

Overland and NIAB secured further funding from Growing Kent & Medway to accelerate research and introduce sustainable, recycled coir media into commercial strawberry production. The project aims to develop energy-efficient, robust methods to eliminate risks from pests, pathogens, and weeds in recycled material; demonstrate the use of recycled media at commercial scale; provide comprehensive agronomy advice; and compare the lifecycle of virgin and recycled coir to assess their economic and environmental benefits.

Results to date

At a commercial site (Kelsey Farms), the everbearing strawberry variety Katrina was planted in virgin Legro coir bags and compared with Overland’s recycled coir in bags, as well as reused coir (directly replanted into old bags). Each coir type was trialled in nine commercial tunnels (over 3,000 bags per coir type), with independent irrigation systems for each.

Unfortunately, during harvest, fruit from virgin and reused coir was mistakenly picked and recorded together. Therefore, the recycled coir was compared with both virgin and directly replanted coir combined. Yields were similar (approximately 1.3kg per plant), with no significant differences in pest (thrips), weed, or crown rot pressure between coir types. However, visible differences in plant growth were noted—plants grown in recycled coir appeared more vigorous and cropped 7–10 days earlier than those in virgin bags.

Plants in recycled media also required 12% less fertigation over the season. This reduction in water use was especially noticeable on hot days. The grower was highly satisfied with the performance and ease of managing the recycled media, and the trial has been repeated this season. In 2024, similar trials were conducted, comparing everbearing varieties grown in recycled coir with virgin coir and a 50/50 mix of the two. This is intended to increase grower confidence and explore further options.

At NIAB’s East Malling site, the everbearing variety Malling™ Supreme was trialled using virgin and recycled Legro and Cocogreen coir in troughs rather than bags. Separate irrigation systems were used for recycled and virgin coir, though not by brand. The two recycled coirs used 4% less water than their virgin counterparts. This was primarily due to a reduced need for wetting up at the start of the season, along with decreased irrigation demand on hot days, thanks to the recycled coir’s higher water-holding capacity.

Overall yield from recycled coir was slightly lower when comparing recycled and virgin Legro material. This is attributed to the virgin coirs of both brands being fairly comparable in water use, while the recycled coirs had different previous growing histories.

In particular, the recycled Legro had a much higher water-holding capacity than recycled Cocogreen, leading to over-irrigation of the former and under-irrigation of the latter—resulting in a slight yield decline. This highlights the importance of adapting irrigation/fertigation regimes to different coir types, or at least using separate irrigation valves to maintain optimal moisture levels.

NIAB’s research has shown that recycling coir offers significantly greater potential than either reusing or composting, with the ability to deliver strawberry yields and quality comparable to virgin material. The rate and extent of physical and chemical degradation vary depending on the coir’s type, manufacturer, and growing history, but cost-effective coir recycling is achievable with minimal loss in yield. However, irrigation and fertigation for crops grown in recycled coir must be managed separately from virgin coir due to lower AFP, or else overwatering may occur—leading to root death and diminished yield and quality.

Further research is planned to refine the recycling process, improving the physical properties and addressing chemical imbalances, as well as residual pests, weeds, and pathogens that may contribute to the small yield drop. Additionally, the root microbiome of strawberries grown in virgin and recycled coir is being studied to uncover any microbial imbalances.

An economic and environmental impact assessment of coir recycling will also be conducted, covering the full lifecycle—from substrate production and use on the farm to final disposal. This will include total costings and environmental footprint analysis.

Source: Hortidaily