Most modern controlled environment plant production operations (e.g., greenhouses and vertical farms) utilize soilless growing media. The majority of the growing media are formulated using materials such as peat moss, coir, wood material, perlite, etc. These materials can be expensive, may have inconsistent availability, and can come with significant carbon footprints during preparation (e.g., peat moss harvesting) and transportation. Further, at the end of each crop cycle, the used growing media and plant residues (e.g., roots, old leaves and stems left with the growing media and any other unsold plant materials) - termed „used media“ in this study- are normally disposed to the environment. Most used media still contain plenty of plant nutrients which can cause environmental pollution. To solve the above issues, we have been working with a local 3-acre, certified organic baby green greenhouse grower to develop protocols for composting their used media and reusing the stable compost for continuous crop production cycles. The goals of this project are to develop protocols for 1) composting used growing media and plant residues, 2) mixing the resulting compost with other materials to formulate new growing media with acceptable physical and chemical properties, and 3) developing rootzone management strategies (e.g., irrigation) to use the new compost-containing growing media for greenhouse baby greens production. This talk will present some of the results collected during this study.

As horticulture faces growing challenges linked to environmental regulations and the depletion of fossil resources, the reuse of spent growing media presents a viable strategy for a more sustainable hydroponic production. By recycling peat-based growing medium, strawberry growers can reduce their dependency on virgin peat and advance the transition to a more eco-friendly cultivation system. Besides, contributing to the circular economy implies lower costs on resources like peat and nutrients. In two greenhouse trials, the effect of multiple reuse and adjusted fertigation was assessed on the plant development and plant health, root development, yield and sorting, fruit quality and both physical and chemical characteristics of the growing medium. In the first trial, varieties Elsanta and Malling Centenary were planted in virgin, 1 year old, 2 year old and 3 year old peat-based growing medium. The age of the medium didn’t influence yield or sorting negatively for both varieties. In Malling, some wilting occurred as result of root diseases, but no significant benefit of steam treatment was observed. Repeated use of the substrate didn’t negatively impact physical properties and maintained a stable nutrient content without harmful accumulation of Na or Cl-salts when standard fertigation was applied. In the second trial, fertigation regimes with reduced P and K input had no significant effect on the performance of the crop. Also the effect on nutrient retention was limited. When fertigation was replaced by water during the last 2 weeks of cultivation, significant reduction of N, P, K, Mg and Ca contents could be observed in the substrate without loss off yield or fruit quality. These trials reassessed successfully the end-of-life status of spend peat in strawberry cultivation and advocate for more reuse in practice.

Peat is extensively utilized as a plant growth substrate component in horticulture. However, due to its non-renewable nature, there is an urgent need to reduce its usage. This study investigates the effect of reusing peat-based growing media in strawberry cultivation up to four times. The objective was to determine whether reusing growing medium affects fruit taste of the strawberry cultivars, Elsanta and Malling Centenary. The titratable acidity (TA) and total soluble solids (TSS) content of the strawberry fruits were analyzed. A panel of 20 individuals conducted a sensory evaluation of the fruits’ aroma, flavor, acidity, and sweetness. The analysis revealed that fruit preference is mainly determined by the cultivar, with Malling Centenary being favored. The tasting test results were in accordance with the TA and TSS content of the fruit. Fruits derived from plants grown in different substrates did not significantly differ in the sensory appreciation, underscoring the limited risk in altered fruit taste upon substrate reuse as a sustainable cultivation practice.