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A propagation trial conducted by fourth-year HAS Green Academy students found that cucumber plants grown in Cultiwool Prime showed stronger plant development, improved root growth and higher populations of beneficial Trichoderma compared with a commercial reference stone wool substrate.
Successful cucumber production begins during propagation. A uniform, well-developed young plant with a strong root system provides a solid foundation for establishment after transplanting and supports consistent crop development throughout the production cycle.
In high-tech greenhouse horticulture, stone wool is widely used because it provides growers with a clean, uniform and controllable root-zone environment. Its physical structure allows precision management of irrigation, nutrient availability, and oxygen around the roots.
The performance of stone wool is influenced not only by its fibres, but also by the binder used to hold those fibres together. Conventional stone wool substrates commonly use phenol-formaldehyde binders produced from petroleum-derived raw materials. Cultiwool Prime is manufactured using a sugar-based, plant-derived binder technology.
Combined with an optimised fibre structure, this natural binder technology is designed to provide uniform water distribution, predictable re-wettability and a stable balance between water and air. These characteristics help growers maintain precise root-zone control throughout propagation and production.
To understand how stone wool composition and structure can influence cucumber propagation, Cultiwool collaborated with fourth-year students from HAS green academy on a six-month Professional Assignment.
Two propagation cycles were conducted using cucumber cultivar ‘Blue Heaven RZ’. The trial compared Cultiwool Prime, which uses a sugar-based biopolymer binder, with Cultiwool Original and a commercially available reference stone wool substrate. The two comparison substrates used conventional phenol-formaldehyde binder technology.
Depending on the treatment, seedlings were inoculated with the beneficial fungus Trichoderma harzianum T-22, challenged with the root-zone pathogen Pythium ultimum, exposed to both microorganisms or grown without either treatment.
The students assessed plant height, internode length, leaf development, leaf area, visual root quality and shoot fresh and dry weight. Nutrient concentrations in the plants and drain water were also analysed, together with culturable populations of Trichoderma and Pythium.
Cultiwool Prime delivered the strongest overall crop performance in the trial, particularly when compared with the commercial reference substrate.
Cucumber plants grown in Cultiwool Prime were generally taller and developed longer internodes, more leaves and a larger leaf area. They also recorded stronger visual root development and higher shoot fresh and dry weights.
These results indicate that Cultiwool Prime provided favourable conditions for early cucumber development during the two propagation cycles. Stronger roots and greater early plant biomass are important advantages during propagation because they can contribute to more uniform batches, reliable transplant quality and vigorous crop establishment.
The findings also support the role of Cultiwool Prime as a precision substrate for professional propagation. Prime Starter Plugs and Growing Blocks are designed to combine uniform moisture control with stable EC behaviour and effective oxygen availability, supporting fast rooting and consistent plant development.
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The physical characteristics of Cultiwool Prime may help explain the stronger plant and root development observed during the trial.
Compared with the denser reference substrate, Cultiwool Prime showed a more open structure and a lower water-holding capacity under the conditions tested. This may have allowed more air to remain available within the root zone after irrigation, supporting oxygen supply to actively growing roots.
Maintaining an effective balance between water and air is essential in cucumber propagation. Roots require sufficient moisture for water and nutrient uptake, but they also need oxygen for respiration and healthy development. A substrate that can be irrigated accurately while retaining adequate air supports more precise crop steering and reduces the risk of an overly wet root zone.
The stronger root scores and above-ground growth measured in Cultiwool Prime suggest that its air–water balance supported active root development under the irrigation strategy used in the trial.
Cultiwool Prime has been engineered to provide consistent water distribution, predictable re-wettability and stable root-zone conditions. This gives professional growers greater control over irrigation timing, moisture levels and EC throughout the crop cycle.
The microbial analysis produced another positive result. Trichoderma harzianum T-22 successfully established in the stone wool, with higher culturable populations detected in Cultiwool Prime than in the commercial reference substrate.
Trichoderma is widely used in professional horticulture because of its ability to colonise the rhizosphere and interact with the plant root system. It can also compete with or antagonise certain root-zone pathogens.
The higher colony counts recorded in Cultiwool Prime indicate that the substrate provided an environment in which the beneficial fungus could establish and persist. This may have been influenced by the physical root-zone conditions, the sugar-based binder system or a combination of both.
The trial did not demonstrate that compounds from the binder were directly used by Trichoderma. Nevertheless, the microbial results show that the natural binder technology did not prevent establishment of the beneficial organism and may have contributed to a more supportive root-zone environment.
No clear effect of either Trichoderma or Pythium ultimum on plant growth was observed during the trial. Plant and disease pressure remained limited, meaning the protective role of Trichoderma and the negative effect of Pythium were not strongly expressed. Importantly, Cultiwool Prime still delivered stronger plant growth and root development under these favourable propagation conditions.
Differences in nutrient behaviour were also identified among the substrates. Drain samples from Cultiwool Prime contained higher concentrations of silicon and manganese and lower concentrations of copper.
These differences may have resulted from mineral release, adsorption or interactions between the nutrient solution and the stone wool matrix. However, they were not associated with visible nutrient disorders or negative effects on crop health during the trial.
The overall plant response remained positive, with Cultiwool Prime producing stronger growth across several crop measurements. This suggests that the observed nutrient differences were not a limiting factor under the conditions of the study.
For professional growers, propagation performance is about more than producing a larger young plant. The objective is to achieve a uniform crop with healthy roots, predictable development and the resilience needed for a smooth transition into the production greenhouse.
The trial demonstrated that Cultiwool Prime can provide a strong foundation for this process. Plants grown in Prime developed more shoot biomass, a larger leaf area and stronger root systems than plants grown in the commercial reference substrate.
These characteristics can support more consistent young-plant quality and crop establishment. A well-developed root system improves the plant’s ability to explore the substrate and take up water and nutrients, while uniform above-ground growth makes it easier to manage irrigation, climate and crop development across the greenhouse.
Cultiwool Prime combines these horticultural benefits with natural binder technology designed to reduce environmental impact without compromising precision or performance. Across the Prime portfolio, the optimised fibre structure supports uniform water distribution, oxygen availability, stable EC behaviour and reliable crop steering.
Under the conditions of the two propagation cycles, Cultiwool Prime was associated with stronger cucumber growth, improved root development and higher culturable populations of Trichoderma harzianum T-22 than the commercial reference stone wool substrate.
Although the trial does not isolate the binder as the sole cause of these results, it shows how natural binder technology, fibre structure and root-zone properties can work together to support plant performance.
For cucumber growers and propagators, the findings highlight the practical value of a substrate that combines accurate irrigation control with favourable oxygen availability and consistent root-zone conditions. By supporting rapid rooting, uniform plant development and reliable crop steering, Cultiwool Prime provides a strong starting point for efficient, high-quality greenhouse production.
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The Professional Assignment gave Cultiwool valuable insight into the interaction between stone wool composition, plant performance and microbial activity. It also provided the participating students with practical experience in greenhouse trials, crop measurements, microbiology and applied substrate research.
For Cultiwool Prime, the findings provide a promising basis for further investigation. The combination of stronger early crop development, improved root scores, and higher Trichoderma populations indicates that sugar-based binder technology may contribute to the development of stone wool substrates designed for both crop performance and a biologically active root zone.
Cultiwool would like to thank HAS Green Academy students Romi, Kjeld, Siddhant and Paula for their dedication, curiosity and professional approach throughout the project. Their work contributes to a better understanding of the stone wool root zone and supports continued innovation in substrates for high-tech greenhouse horticulture.
In professional greenhouse horticulture, growers often perform side-by-side trials to evaluate which substrate best supports their crop and cultivation strategy. A well-designed trial improves decision-making and helps identify the most efficient and reliable solution for consistent production.
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There are many aspects affecting the decision of which substrate to use, among these crop types and cultivation stages. Similarly to the way soil mixtures can be amended and customized, so are stone wool products tailor-made for the cultivation of a specific variety of crops. Stone wool can be manufactured in such a way that the density and orientation of the molten rock fibers determine the moisture holding capacity, air-filled porosity, and moisture gradient within the blocks.
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From a young age, we were taught not to try to fit a square into a circle. Child games utilizing different shapes emphasized this even more with specific shaped objects only fitting in the same shaped hole. And thus comes one of the most common stone wool questions we get. Why do people use a square propagation plug (AO) when the hole in the block is round? Well, there are a couple of different reasons why one might choose to use either a square Cultiwool plug (AO) or a round Cultiwool plug (i.e., macroplug). This article will elaborate on these reasons;