The phase-out of peat by 2030 poses a significant challenge to the horticultural sector in Germany. This study investigates the ecological impacts of reducing or eliminating peat in substrates within established cultivation systems.

The study's methodology involved developing a typical production system for potted basil in collaboration with herb growers and industry experts, with primary data collected through surveys and validated in focus groups. This data informed the creation of a theoretical model representing scenarios with reduced peat content and peat-free production, considering both winter and summer cultivation.

Factors such as increased fertilizer use, irrigation volumes, and extended cultivation periods were incorporated into these scenarios. The Product Carbon Footprint (PCF) of a 13 cm basil pot, ready for distribution, was calculated using the Hortifootprint Category Rules, based on the European standard for the Product Environmental Footprint. The assessment boundaries extend from the raw materials of the production to the finished product, covering the entire cradle-to-gate lifecycle.

The results show that a reduction in peat content reduces the PCF in summer production by 8% from 0.469 kg CO_2e to 0.430 kg CO_2e per unit, with a further reduction to 0.387 kg CO_2e in peat-free production, a decrease of 17%. In winter, reducing peat content lowers the PCF by 3%, from 1.530 kg CO_2e to 1.490 kg CO_2e per unit. However, peat-free production with an extended cultivation period increases the PCF to 1.631 kg CO_2e per unit, a 7% increase. Although increased fertiliser use and water consumption partially offset carbon savings, peat reduction still contributes to lower overall carbon emissions.

The study’s limitations arise from the use of theoretical models and assumptions due to limited practical experience. Nonetheless, these findings provide valuable insights for transitioning to more sustainable horticultural practices.

Composts are considered to be a sustainable component of horticulture growing substrates that can be used in Organic production systems. Some composts are capable of offsetting, or replacing, traditional fertilizer applications, however there is a high level of variability reported in the effectiveness of composts used as fertility sources. In this study, we collected >100 commercially available compost sources from across the United States and assessed their suitability as a growing media for Organically grown tomatoes. The composts surveyed were categorized as yard trimmings (YT), yard trimmings composted with food waste (YTFW), or yard trimmings composted with animal manure (YTM). The composts had wide ranges of electrical conductivity (EC), total nitrogen (TN), nitrate (NO3), ammonium (NH4), C:N ratio, bulk density, and cation exchange capacity (CEC). Two mixes (100% compost, and a 1:1 v/v compost:peat mixture with chicken litter added as a fertility source to deliver an additional 0.7 lbs TN/YD3) and a control mix consisting of peat alone and synthetic fertilizer were planted with Tomato cv. Mountain Merit plugs. After 4 weeks, the plants were harvested at the soil line and weighed. As expected, plants grew very differently based on chemical properties and mixture rate. Plants grown in the composts with high NO3-N (>10 ppm), TN (>0.65), and CEC (>25), and low C:N (<20) typically grew similar to, or better than, the control treatment. Plants grown in compost with low TN and high C:N typically showed poor growth which was largely attributed to immaturity or N immobilization, and these media would be considered unacceptable for commercial production. Although the variability across composts were relatively high, compost chemical properties were highly predictive of compost suitability. Further refinement of these key parameters should improve commercial grower’s confidence in compost use in Organic production systems and help to offset the use of traditional fertilizer inputs.  

The increasing use of soilless cultivation systems in horticulture has driven a rising demand for growing media. With regulatory restrictions on peat use and increased demand for growing media, growing media producers are seeking raw materials in quantities exceeding 100 000 m³ per year, which must be available with reliable quality. In this study, several renewable raw materials were tested including miscanthus (extruded, chopped, and co-composted with green wastes), hemp, bark (extruded and composted), and woody biochar. The raw materials were characterized in the lab and tested in the greenhouse as mixtures of 49% peat, 21% coir, and 30% tested materials, as well as one peat-free mixture (20% wood fibre, 20% composted bark, 20% extruded bark, and 40% coir). Peat-based mixtures containing 30% biochar, miscanthus co-compost, or extruded bark showed plant growth comparable to the reference peat-based mixture. For hemp, chopped miscanthus, and extruded miscanthus, adjustments to base fertilizer dressings and fertigation regimes (frequency and nutrient strength) improved plant growth. In the peat-free mixture, plant growth was reduced by about 25% compared to the reference substrate. The findings highlight the importance of substrate processing, base fertilizer dressing, and fertigation management in cultivation using renewable raw materials.

Increasingly retailers are requiring plant producers to provide containerised plants in peat free growing media, given the negative ecological and environmental impact of peat extraction. Identifying suitable alternative soilless substrates for use in annuals plant production is an ongoing challenge for producers. In this glasshouse study, nine peat free alternative experimental blends, including one commercial blend, were compared to three commercial growth media, consisting of a 100% peat and two peat reduced (65%) growing media mixes. The experimental growth media were create by using organic materials, including woodfibre, coir, composted bark, composted green waste and sphagnum moss, and the inorganic material, perlite, in various proportions and combinations. Their impact was tested on seven different plant species and cultivars. The plant species used in this study were Begonia cucullata var. hookeri (A.DC.), Gazania rigens (L.) Gaertn., Impatiens walleriana Hook. f. and Lobularia maritima (L.) Desv. Plant plugs were transplanted into 10.5cm grey plastic pots and grown in a glasshouse for a period of 10 weeks. Chemical and physical characteristics of all 12 soilless substrates were assessed. Evaluation of the plants was based on fresh and dry weight plant biomass. Additionally a qualitative evaluation of the plants and their root development was completed. The evaluation of the plant quality was assessed by an expert group, while root quality evaluation was carried out using a pictorial grading system and completed by persons in the field of research.