Sassy. Frassy. Keep it Classy.

Sassy. Frassy. Keep it Classy.

What is “frass” and why should it be in your garden?

Hello and good day fellow Symtonians! Welcome to this month’s Symton LEARN segment, where we create content to educationalize your brain with bug stuff! Seriously, we’re excited to be growing and learning alongside you as we dive into topics related to sustainability, agriculture, and of course - insects! Last month, we learned all about our trusty pal, the black soldier fly. Thus, we thought it most fitting to dig a little deeper into what this amazing insect can do, starting with…


AKA, insect “frass”

One of the lesser known, yet important benefits of the black soldier fly larvae lies in its ability to convert low-quality organic material into high-quality fertilizer. Yes, that’s right. We’re talking about bug feces. Here’s why it's cool:

  • It is a substantial source of plant-digestible chitin
  • Helps fight disease, pests, and other pathogens
  • Recaptures nitrogen and phosphorus to be used as fertilizer
  • Aids in balancing the pH level in soil
  • Contains various types of beneficial microbes and nutrients
  • Reduces heavy metals from waste stream
  • Symton BSFL frass is 100% organic

  • Frass and Nitrogen

    One study showed that the highest nitrogen uptake in vegetable crops was achieved by using frass, and proved especially powerful when combined with NPK supplements. However, frass alone outcompeted its commercial competitor, Evergrow (Anyenga, A.O. et al, 2021). This is important because plants need adequate amounts of nitrogen in order to grow! Not only that, but they need it in a form that is “digestible”- frass fertilizer contains tons of beneficial microbes which support the mineralization process of nitrogen, allowing your plants to thrive. 

    Frass and Chitin

    Frass may have a lower NPK ratio than many commercially available fertilizers, but what it lacks in numbers it makes up for in chitin. It is one of the only sources of plant-digestible chitin, as the frass itself is essentially broken down plant material, embedded with all sorts of beneficial microbes and minerals fresh from the gut microbiome of the larvae that processed it. Chitin is responsible for regulating and stimulating plant growth, inducing or enhancing defense mechanisms in plants, disease control, and much more (Shamshina, et al, 2019). Frass is a powerful tool that sustainably supports your plants’ long term health by releasing its nutrients slowly. Ever heard of living soil? BSF Frass is a key contributor, and scientists all over the world are jumping to learn more (Kenyan Agripreneurs:

    Frass and Heavy Metals

    In an increasingly urban environment, fungal and bacterial diseases aren’t the only problems we face as agriculturalists. Heavy metals intoxicate our soil, our waste, and our waters. However, black soldier fly larvae boast the super-power ability to accumulate heavy metals into their tissues, thereby removing it from the environment and preventing it from re-entering in their waste product: frass. In one study, researchers tested BSFL by adding toxic levels of mercury to the food they ate and monitored what came out on the other end- a non toxic byproduct (Basri et. al, 2022). This was a turning point in BSFL research, as it proved that one insect had the capability to remove, or significantly reduce, heavy metals present in our waste streams. Something to think about when considering frass against common synthetic fertilizers, which often contain toxic elements and directly contribute to the global waste problem. This research is an excellent example of how insects can be used to prevent toxicity in the things we consume!

    How much Frass do I need? 

    Frass can be beneficial, but should always be used in the proper amount: 

    Approximately 1 cup of frass per 1 cubic foot of soil OR

    ½ - 1 cup of frass for 1 gallon of potted soil OR

    ½ cup of frass for 1 gallon of water

    To make frass tea, let the frass steep in water for 2-5 hours before application. Thoroughly drench the base of the plant and avoid hitting the foliage. Refrigerate leftovers for up to one week. 

    For ongoing treatments, take a small handful of frass and gently massage it into the surface soil. Repeat once every month or so.

    *Remember, frass is a highly concentrated substance and can be toxic to plants if overused or overapplied. Use in moderation.

    Different plants will produce different results, but remember: using frass is the best way to help your soil help itself. Anyone can use frass- we sell 5lb, 10lb, and 20lb bags right on our website with affordable shipping anywhere in the United States.

    A Frassy Experiment!

    Over the last few months, we collaborated with local New Jersey gardener Elyse Schear on a frass experiment in her vegetable garden! Elyse is a retired research librarian with a green thumb who was excited to test the powers of bug poop for the first time. In May, she planted the seeds of three vegetable crops in large pots in her outdoor garden: Mizuna lettuce, spinach, and cabbage. Two tablespoons of frass were added to the soil of each plant-to-be. Each vegetable had a twin that she used as the control (no frass), so that a proper comparison could be made for each type of plant. 

    Elyse reported back in July with interesting results: both the cabbage and Mizuna lettuce plants benefited from an application of frass, noticeably outgrowing its frass-less counterparts. The spinach, however, did not seem to respond to the addition of frass. This can be due to a variety of factors, as plants are highly dependent on circumstantial elements like regional soil quality, humidity, inclement weather, watering schedule, pests, etc. We encourage you to try your own experiment this growing season, and let us know what you find! 


    Mizunah lettuce with frass (left, top) and without frass (right, bottom). June 2023. Elyse Schear.

    Cabbage with frass (left) and without frass (right). June 2023. Elyse Schear.














    Spinach with frass (left) and without frass (right). June 2023. Elyse Schear.

    Thanks for reading and see you next time on Symton LEARN!


    Anyega, A. O., Korir, N. K., Beesigamukama, D., Changeh, G. J., Nkoba, K., Subramanian, S., van Loon, J. J. A., Dicke, M., & Tanga, C. M. (2021). Black Soldier Fly-Composted Organic Fertilizer Enhances Growth, Yield, and Nutrient Quality of Three Key Vegetable Crops in Sub-Saharan Africa. Frontiers in Plant Science, 12.

    Basri, Noor Ezlin, et al. “Potential Applications of Frass Derived from Black Soldier Fly Larvae Treatment of Food Waste: A Review.” Foods, vol. 11, no. 17, 2022, p. 2664,

    Kenyan agripreneurs fly high with black soldier flies. (n.d.). ACIAR. Retrieved July 20, 2023, from:

    Shamshina, Julia & Oldham, Tetyana & Rogers, Robin. (2019). Applications of Chitin in Agriculture. 10.1007/978-3-030-16581-9_4.


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