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Sustainable soil solutions: Combining Biochar and Insect Frass for improved plant and soil health
Charlotte Thompson, Codi Treacy, Swagata Sarkar, Georgina Michael, Jashkumar Jaysukhbhai Davra, Chelsia Viju ● 2026-03-31 ● Research
Charlotte Thompson, Codi Treacy, Swagata Sarkar, Georgina Michael, Jashkumar Jaysukhbhai Davra, Chelsia Viju ● 2026-03-31 ● Research
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Through Flinders University’s Science Connect program, our team partnered with Mobius Farms to investigate how sustainable soil amendments could improve plant growth and soil properties. Two solutions that we investigated were biochar, a carbon-rich material that improves soil structure and nutrient retention, and black soldier fly frass, a nutrient-rich organic fertiliser containing beneficial microbes.
While both sources have shown benefits individually, emerging research suggests they may work even more effectively together. Biochar’s porous structure can act as a carrier for frass nutrients and microbes, potentially enhancing nutrient availability and supporting a healthier soil ecosystem. To test this, we grew rocket (Eruca sativa) seedlings in both ‘high’ and ‘low’ nutrient soils, comparing biochar and frass alone, as well as different combined ratios.
Sustainable horticulture focuses on efficient, high-quality food production while maintaining soil health. Unlike traditional fertilizers, a combination of biochar and frass can be used as sustainable soil amendments:
Despite many positive effects, both amendments require careful consideration regarding feedstock selection and production protocols to ensure quality and avoid contaminants before future commercialisation.
To investigate whether biochar and frass worked better separately or together, we tested the growth rates of rocket seedlings. The biochar was sourced from Schutz Winery (2025 vineyard cuttings) and used in a fine dust form, while the frass was sourced from Mobius Farms’ own colony.
Our study design utilized two main soil treatments:
We tested various ratios, including a control group, frass-only (10% volume), biochar-only (20% volume), and combined mixtures at 10%, 20%, and 50% volume. We “loaded” the biochar by soaking it with frass in water for 2 hours prior to planting. Over seven weeks, we measured shoot height, leaf colour, root length, and soil nutrient composition.
The results determined that the rocket plants grown in low nutrient soil with the 10% biochar and frass mixture had the highest growth rate, reaching 43 cm. Conversely, plants in high-nutrient soil with the 50% mixture had the lowest growth rate (23 cm).
Interestingly, stress flowering was observed in almost all treatments except for the high-nutrient frass-only and 50% combined treatments, which appeared the healthiest despite slower vertical growth. We identified several limitations for future study, including the need for a fully controlled greenhouse environment and germinating from seeds to ensure initial plant consistency.
Overall, our experiment showed that biochar and black soldier fly frass have a positive effect on growth, but the results are highly dependent on the existing nutrient content of the soil and the application rate. While we initially hypothesised a 20% mixture would perform best, the 10% treatment in low-nutrient soil proved to be the most effective balance. This strategy represents a promising step in Mobius Farms' dedication to circular and sustainable soil solutions.
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