Black Soldier Fly (BSF) frass is rapidly gaining recognition as a powerful and sustainable tool in agriculture. This byproduct of insect farming is not just another organic fertiliser—it’s a versatile soil amendment with unique characteristics that set it apart from traditional inputs. In this guide, we’ll explore what BSF frass is, its types, how it compares to other organic fertilisers, and how to use it effectively to enhance crop productivity.
What Is Frass?
Frass is the term used to describe the residue left behind by insects, including their feces and any uneaten organic material. For Black Soldier Fly (Hermetia illucens, BSF) farming, frass is the byproduct of larvae feeding on organic waste. According to the International Platform of Insects for Food and Feed (IPIFF), BSF frass is defined as “the byproduct of insects consisting of excreted material and any residual substrate not consumed by the insects.”
But frass is more than just waste—it’s a nutrient-rich, bio-active organic material with numerous applications in agriculture. Studies have shown that frass can act as a biofertiliser, providing essential nutrients, and as a biostimulant, enhancing plant growth and health. Its bioactivity includes plant elicitor effects, stimulating plant defenses against pathogens and environmental stressors.
Types of Frass
Not all frass is created equal. Depending on its processing and composition, BSF frass can be categorized into several types:
Not all frass is created equal. Depending on its processing and composition, BSF frass can be categorized into several types:
Not all frass is created equal. Depending on its processing and composition, BSF frass can be categorized into several types:
Un-composted Frass: Raw frass that hasn’t undergone composting. It retains its nutrients but may have high ammonia/urea levels or organic acids, making it less suitable for direct application or use for young plants.
Composted 100% Frass: Frass that has been fully composted, mineralizing nitrogen and reducing phytotoxicity. ProdTypes of Frass
Not all frass is created equal. Depending on its processing and composition, BSF frass can be categorized into several types:
Composted Frass Mixed with Carbon Sources: Frass composted with materials like sawdust, straw, or oil palm waste. The added carbon can increase the C:N ratio but it means customers rarely know precisely how much of what they are buying is frass.
Un-composted Frass Mixed with Other Ingredients: Raw frass blended with inorganic fertilisers or organic additives. These products are typical in countries like Malaysia where regulations do not require ingredient labeling. A mixed product may be beneficial or detrimental depending on what is added.
Liquid Extracts of Frass: A new and innovative category of frass products, liquid extracts are highly bioavailable and act as biostimulants. Products like Vitalis® offer a concentrated source of nutrients and beneficial microbes, ideal for foliar applications, targeted soil drench or use in fertigation / hydroponic systems.
Frass vs. Other Organic fertilisers*
BSF frass stands out among organic fertilisers due to its unique composition and benefits:
High Organic Matter with Low C:N Ratio: Unlike many traditional composts with high carbon content and a C:N ratio above 25, BSF frass often has a much lower ratio, minimizing the risk of nitrogen immobilization in soils.
Rich in Humic Substances: Composted BSF frass contains humic and fulvic acids, which improve soil structure, enhance nutrient retention, and support long-term soil fertility.
Plant Elicitor Effects: Frass contains bioactive compounds, including chitin, that stimulate plant immune responses. This “priming” effect can help plants resist common pathogens and environmental stressors.
Disease Inhibition: A growing body of evidence from researchers around the world suggests that BSF frass has potential inhibitory effects on pathogens such as Fusarium and Phytophthora among others
Compared to conventional composts and fertilisers, BSF frass delivers a combination of organic matter, nutrients, and biostimulant effects that make it a versatile tool for both soil health and plant resilience.
*Note that we are using the term fertiliser to refer to frass products in this article. However, depending on your geography and NPK values of the frass being used the frass product may be defined differently such as a soil amendment.
How to Use BSF Frass
The application of BSF frass depends on your agricultural goals. Here are three scenarios and how to use frass effectively:
1. To Rebuild Productive Soils
For depleted soils with low organic matter (OM), BSF frass provide excellent value for nutrients. A standout feature of BSF frass is its high organic matter content which can reach 75-70% in contrast to most composts or organic fertilisers with 30-60% OM. Unlike traditional composts, you need much smaller quantities to achieve the same increase in soil organic matter and because the OM is mostly in the form of humic substances it will be resilient and stay in the soil.
Example: Calculate the organic matter needed to raise your soil’s OM content to the target range (e.g. 3%) and apply the corresponding amount of frass over a cropping season. Re-test your soil the following cropping season and adjust the dose as required.
2. As a Biostimulant
Liquid extracts of frass, such as Vitalis®, are ideal for promoting new growth, boosting plant vigor and stimulating plant defences.
When to Apply: Use during the establishment phase of young plants, after transplanting, or prior periods of disease susceptibility .
How to Apply: Dilute the liquid extract according to the manufacturer’s instructions and apply as a foliar spray or drench to maximize bioavailability and stimulate growth.
3. To Improve Plant Disease Resistance
To reduce the risk of disease, frass can be applied to prime plant defenses. The bioactive compounds in frass, such as chitin, help stimulate the plant’s immune system. Keep in mind that ellicitors like Chitin cannot usually help a plant that is already infected, just as a vaccine in humans protects against future infections chitin should be applied early to prevent disease rather than treating it.
When to Apply: Add frass at the nursery stage, during transplanting, or before the onset of common diseases.
Benefits: Boosts plant resilience against pathogens like Phytophthora, potentially reducing losses from disease.
A Sustainable Tool for Modern Agriculture
It is not very common that new forms of organic fertilisers become available. Most organic fertilisers are made of up of some form of organic matter that has been subject to a relatively standardized composting system. Black Soldier Fly Frass is different. When processed correctly it is an organic biofertiliser that offers a distinct set of solutions to farmers at a time when agriculture needs innovative solutions to respond to climate change. But even though these products are new to agriculture does not mean they are new to plants. If you visit your local forest look under the leaves in the understory: you will likely see many small round balls: frass. In many ecosystems frass provides a significant portion of nitrogen deposition and plants very likely evolved systems such as the ability to detect chitin in frass due to its ubiquity in the natural environment. In terrestrial ecosystems frass can provide plants with information about their surroundings and be a source of important microbes.
Its versatility, from improving soil organic matter to acting as a biostimulant and disease inhibitor, makes frass an exciting innovation for farmers looking to enhance productivity while maintaining environmental stewardship. With fully composted frass biofertilisers like Diptia® and Vitalis®, the potential of BSF frass is only beginning to be realized.
Comments