In the bustling nurseries of the UK, where growers are racing to meet the 2025 peat ban, one common strategy has been to ramp up fertilizer to compensate for the shift from traditional peat-based media. However, recent research challenges this approach, suggesting that excess nutrients may do more harm than good.
Key Findings from Commercial Peat-Free Trials
The Royal Horticultural Society (RHS) has conducted extensive trials across UK nurseries, focusing on the nutritional needs of plants in peat-free substrates. These studies, spanning three years and involving herbaceous perennials, shrubs, and trees, compared peat-free growing media from five manufacturers against peat-reduced controls under standard commercial conditions. The results indicate that increasing fertilizer application does not enhance plant performance and can instead impede growth and root establishment. According to the trials, peat-free mixes—often biologically active and pre-loaded with nutrients from raw materials—require a recalibrated feeding regime. After 14 months, peat-free plants exhibited no nutrient deficiencies, while some peat-reduced plants did, despite identical fertilizer rates. This underscores the distinct chemical and physical properties of peat-free substrates compared to the stable, low-nutrient profile of peat.
Implications for Grower Practices and Costs
The findings highlight several practical implications for the horticulture industry as it transitions to sustainable growing media:
- Resource Efficiency: Overfeeding leads to unnecessary costs and environmental leaching. For instance, reducing fertilizer by just 1kg per cubic meter could yield significant savings across large-scale operations, while minimizing nutrient runoff into waterways.
- Crop-Specific Optimization: Trials emphasize the need for individualized testing, as the “sweet spot” for nutrition varies by plant group and media type. Growers relying on pre-mixed nutrients in media—common in the UK—may be able to cut additional inputs without compromising yields.
- Environmental Benefits: By avoiding surplus fertilizer, growers can reduce ecological impacts, aligning with broader sustainability goals amid the UK’s peat-free mandate.
Dr. Raghavendra Prasad, RHS Transition to Peat-Free research fellow leading the studies, noted:
"This means feeding needs to be approached differently and traditional nutrition regimes that were based on peat systems may need to be modified."
These insights build on the 2023 RHS Industry Survey, which identified plant nutrition as a top concern for peat-free adoption, alongside irrigation and costs. The ongoing fellowship collaborates with eight major UK growers and six media manufacturers to provide science-based guidance, fostering a smoother industry shift.
The Role of Collaboration and Further Research
Collaboration between growers and manufacturers emerges as a critical factor in optimizing peat-free systems. Manufacturers can detail inherent nutrient profiles, while growers contribute on-site performance data, enabling tailored formulations. Dr. Prasad advises:
"Carrying out collaborative trials with your growing media manufacturer, comparing the amount of fertiliser you currently add with the results you get from adding slightly less and slightly more, will help to identify how much your plants actually need."
For example, if a grower typically adds 4kg of fertilizer per cubic meter, testing 3kg and 5kg variations could inform future specifications, building a knowledge base for peat-free practices. Irrigation management intersects with nutrition, as overwatering accelerates leaching. The trials, following 2024’s irrigation-focused results, show that precise watering enhances nutrient retention, indirectly supporting growth while cutting expenses and environmental harm.
"By optimising irrigation, you are indirectly addressing nutrition. Keeping nutrients available to plants by reducing leaching improves growth while reducing environmental impact and expense to growers," explained Prasad.
While these initial results are promising, they remain indicative rather than definitive, with ongoing trials needed to address uncertainties in long-term performance across diverse conditions. The 2025 RHS Peat-Free Horticulture Conference, themed around nutrition, brought together experts, scientists, policymakers, and industry leaders to discuss these challenges and solutions. How do you see these findings shaping your approach to sustainable growing practices in the coming years?
