An Introduction to Frass!




Frass is created through the digestive process of Hermetia ilucens, commonly called black soldier fly (BSF) (Quillam et al. 2020). This process involves BSF transforming organic waste into a high quality manure (Boccazzi et al. 2017). BSF manure contains high levels of proteins, fats and minerals, which have proven to be an excellent organic fertiliser for plants (Beesigamukama et al. 2020). Frass contains high concentrations of nitrogen, phosphorous and potassium which plants require to grow healthy foliage, strong roots, stems, flowers and fruits. Studies have found frass to outperform other organic fertilisers, like compost, likely due to its high mineralisation rate resulting in better supply and availability of nutrients to plants (Beesigamukama et al. 2020). Frass has also been found to increase drought resistance and salt tolerance in various plant species (Beesigamukama et al. 2020). A variety in the diet of BSF results in a diverse composition of frass offering a wide supply of nutrients and organic matter to soil, and promoting varied microbial communities and supporting plant behavior (Schmitt and Vries 2020). Frass also encourages healthy ecosystems, with studies showing the addition of frass to soil can encourage more pollinators, larger plant growth, plus greater production of flowers and seeds (Schmitt and Vries 2020). BSF frass presents an exciting, sustainable method for recycling and upgrading low value food waste and animal tissue materials, into a rich organic fertiliser.




Chitin is the main component of insect and crustacean exoskeletons, and the cell wall of fungi. Insect larvae are rich in chitin. As the larvae develop and grow, they repeatedly shed their exoskeleton which is then left behind in the frass (Quillam et al. 2020). Insect frass is the only plant digestible form of chitin. It has been demonstrated that the frass has the ability to induce beneficial modifications in soil microbiome, and to promote healthy ecological systems through suppressing pest pressures (Schmitt and Vries 2020). Chitin elicits a range of defense responses in host plants in response to microbial infections (Hadrami et al. 2010). A recent study has found the application of BSF frass can attract wasps, which prey on pests, and subsequently protect crops from pest damage (Schmitt and Vries 2020). Another study found soil amended with chitin to increase total actinomycetes population (beneficial soil microbes that breakdown resistant forms of organic matter that plants cannot degrade), and produce a potato harvest with significantly less tuber scab than the untreated soil (Hadrami et al. 2010). Chitin naturally creates antimicrobial peptides when under environmental stress by making mineral nutrients inaccessible to pathogens and halting the discharge of pathogenic mycotoxins (Choi and Hassanzadeh 2019). This process forms defense against pathogens from harming the plant, while successively stimulating the growth and activity of beneficial microbes in the soil (Sharp 2013).


Chitin’s biochemical compounds are similar to that of the cellulose found in plant cell walls (Sharp 2013). Akin to cellulose, chitin supports the mechanical and physical barriers that offer structural strength and combined with other compounds helps facilitate stronger plant tissue (Sharp 2013).



Green Man Char recommends applying biochar + frass or frass by mixing it into the root zone with soil or applying as a top dressing for established plants. Application rates and frequency vary depending on plant nutrient requirements. In general, fertiliser application is more beneficial when the concentration is low yet applied regularly (less runoff, less nutrients taken up by weed species, less chance of root burn, etc). Our biochar + frass products can be used with other fertilisers and soil conditioners, however, care should be taken to not over-fertilise the soil. The addition of biochar to the frass results in a more slow release fertilizer. Biochar and frass compliment each other extremely well, it is a fantastic product for all gardens, farms and plants! 

 Here we applied a blend of biochar, frass, compost, worm castings and wood vinegar to replete soil after growing demanding brassica crops over winter:





Beesigamukama, D., Mochoge, B., Korir, N.K., Fiaboe, K.K., Nakimbugwe, D., Khamis, F.M., Subramanian, S., Dubois, T., Musyoka, M.W., Ekesi, S. and Kelemu, S., 2020. Exploring black soldier fly frass as novel fertilizer for improved growth, yield, and nitrogen use efficiency of maize under field conditions. Frontiers in Plant Science11.


Choi, S. and Hassanzadeh, N., 2019. BSFL Frass: A Novel Biofertilizer for Improving Plant Health While Minimizing Environmental Impact.


El Hadrami, A., Adam, L.R., El Hadrami, I. and Daayf, F., 2010. Chitosan in plant protection. Marine drugs8(4), pp.968-987.


Schmitt, E. and de Vries, W., 2020. Potential benefits of using Hermetia illucens frass as a soil amendment on food production and for environmental impact reduction. Current Opinion in Green and Sustainable Chemistry.


Sharp, R.G., 2013. A review of the applications of chitin and its derivatives in agriculture to modify plant-microbial interactions and improve crop yields. Agronomy3(4), pp.757-793.


Varotto Boccazzi, I., Ottoboni, M., Martin, E., Comandatore, F., Vallone, L., Spranghers, T., Eeckhout, M., Mereghetti, V., Pinotti, L. and Epis, S., 2017. A survey of the mycobiota associated with larvae of the black soldier fly (Hermetia illucens) reared for feed production. PLoS One12(8), p.e0182533.



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