What Is Frass?

Insects are the future! We often hear this statement, especially when it comes to food! And indeed, edible insects are increasingly present on our shelves. But these insects also produce waste that is also increasingly popular in our gardens: frass!

Where Does Frass Come From?

To fully understand where frass comes from, we need to take a few moments to look at the major global trend of incorporating edible insects into our human and animal diets. Indeed, insects are increasingly added in feed mixes for livestock. Because insects are very easy to raise and propagate, edible insect farms have grown exponentially. And of course, as with any industrial production, we ended up with a waste product: frass. So it was while looking for ways to reuse this material that its benefits for the garden were discovered.

Frass is therefore composed of insect excrement, exuviae (the old mutating skins of insects), fragments of exoskeletons and microorganisms. Frass can come from different insect farms, but it is the black soldier fly (Hermertia illucens) which is the most famous. In the industry, it is often called BSF. But other insects, such as the two-spotted crickets (Gryllus bimaculatus), the silk moth (Bombyx mori), the African golden emperor moth (Gonimbrasia krucki), the mealworm (Tenebrio molitor), the desert locust (Schistocerca gregaria), the Garden fruit chafer (Pachnoda sinuata) and the rhinoceros beetle (Oryctes rhinoceros) are used for frass production.

What Makes Frass So Special?

First, frass is interesting because it is a great example of circular economy. Insects are raised for food and the residue is collected to make a garden fertilizer: frass. There are few or no chemical inputs, no processing that generates toxic pollutants in the air… Frass is dried, ground and packaged. It is therefore a very interesting natural product.

But what turned out to be most interesting about frass is its fertilizing capacities. It’s been less than 10 years since any real studies have looked at the properties of frass. So it’s a very recent product on our shelves. And it turns out that it’s a very good natural fertilizer! My garden trials also confirm this statement.

For those who have been wondering since the beginning of this text where the word “frass” could possibly come from: it is quite simply a German word relating to animal nutrition.

What Does Frass Contain ?

Most of the studies I’ve read prove that frass is an excellent fertilizer, particularly rich in nitrogen and phosphorus. Depending on the insect’s source, there are also amounts of potassium, magnesium, calcium, and sulfur. In smaller doses, there are also traces of manganese, copper, iron, zinc, boron, and sodium. It’s therefore a very complete fertilizer.

The frass of black soldier flies is richer in nitrogen and potassium. That of crickets is richer in phosphorus, and that of grasshoppers produces phosphorus that remains available in the soil for a longer period.

Also, it has been discovered that constant use of frass stimulates microbial life and increases the presence of microscopic bacteria and fungi that are essential for a living soil.

And as if it took more convincing, we are beginning to discover that frass also has the ability to control certain diseases.

How to Apply it?

Being a fertilizer marketed in the form of coarse powder or granules, it is incorporated into the soil, only in the first 10 centimeters (3 inches) of depth. Its effectiveness lasts for several weeks. Some manufacturers recommend an application every month. Most studies confirm that frass releases fertilizing materials over a period of 60 to 90 days, on average. For my part, my first experiments confirm that two applications should be made per growing season, one in spring, at the time of transplanting and another 6 to 8 weeks later. Personally, I have really observed tangible results with the use of frass, unlike biochar, which is also a newcomer in the world of amendments and natural fertilizers.

In short, there’s still a lot to discover about frass and its properties. But for now, the future seems paved with small carcasses and dried insect excrement! And we love that!