Insect Frass 101: The Aussie Gardener’s Secret Weapon 🌱

“Another great product from the Dr.Greenthumbs team.” – Jason Smith
“…noticed a massive decrease in gnat numbers! Happy days!” – Josh Van Limbeek 

Insect frass is one of the most underrated organic soil amendments in Australia. It improves soil biology, boosts plant resilience, and supports natural pest resistance—all with minimal effort.

Whether you're growing vegetables, flowers, or fruit trees, frass can help you build a living soil that works with nature instead of against it.

Table of Contents

• What is frass in plain English?
• Pest frass vs insect frass fertiliser
• Why insect frass can vary between products
• Why Gardeners Swear By Frass
• How to Use Dr Greenthumbs Insect Frass
• Using insect frass for indoor plants
• Frass for seedlings and transplants
• Frass vs Worm Castings: The Quick Low-Down
• Step-by-Step Application
• Insect frass tea: when it makes sense
• Frass in compost: a small boost that goes a long way
• Using insect frass with other soil amendments
• Composted vs fresh insect frass: what gardeners should know
• What research says about insect frass
• Frequently Asked Questions
• Next reads for building stronger living soil

If you want the easiest way to start using frass, these are the most practical options:

What is frass in plain English?

Frass is insect waste, but in gardening it’s not just “bug poo”.

Good insect frass is a mix of insect castings, leftover feed material and tiny bits of shed exoskeleton. That shed exoskeleton is the important bit, because it contains chitin — the same kind of structural material found in insect shells.

In simple terms:

• Frass found on damaged plants usually means pests are feeding.
• Insect frass sold as fertiliser is a processed soil amendment.
• Black soldier fly frass is one of the most common types used in organic gardening.
• Composted or stabilised frass is what you want for soil use.

The easiest way to think about it? Frass is a biological soil input first and a fertiliser second. It adds nutrients, yes, but the bigger win is how it supports soil life, microbial activity and natural plant resilience over time.

That’s why it fits so well in living soil. You’re not force-feeding the plant. You’re feeding the system around the roots.

Pest frass vs insect frass fertiliser

One common point of confusion is the word frass itself.

In everyday gardening, frass can mean two very different things:

• Pest frass - droppings left behind by insects like caterpillars, borers, or beetles feeding on your plants or timber
• Insect frass fertiliser - a processed soil amendment made from beneficial insects (most commonly black soldier fly larvae)

Pest frass is usually found:

• On leaves, branches, or around entry holes
• As fine sawdust, pellets, or gritty debris
• Alongside visible plant damage

In this context, frass is a warning sign, not a soil input. It tells you insects are actively feeding and action may be needed.

Insect frass fertiliser, on the other hand:

• Is collected during controlled insect farming
• Is stabilised and prepared for soil use
• Contains nutrients, beneficial microbes, and chitin

Throughout this guide, when we talk about insect frass, we’re referring specifically to processed black soldier fly frass used to support soil biology, not pest droppings found on plants.

Understanding the difference helps avoid confusion — and ensures frass is used in the right way, for the right purpose.

Why insect frass can vary between products

Insect frass isn’t just one single ingredient.

Depending on how it’s produced, frass can contain:

• Insect castings (digested organic matter)
• Shed exoskeleton material (a natural source of chitin)
• Small amounts of residual feed material
• Beneficial bacteria and fungi

This means the exact nutrient profile and microbial activity of frass can vary between producers.

Factors that influence this include:

• What the insects were fed
• How long the frass was aged or composted
• Whether it was blended with other organic materials

Rather than thinking of frass as a fixed fertiliser, it’s best viewed as a biological soil input - one that works by supporting soil life first, and plant growth second.

That’s also why frass performs best when used regularly in living soils, alongside compost, mulch, and organic matter.

Why Gardeners Swear By Frass

• Explosive microbial life – up to 20 × more biology than worm castings means faster nutrient cycling and healthier soil.

• Chitin triggers plant immunity – roots detect chitin fragments and switch on natural defence pathways against pests and pathogens.

• Improved soil structure & water-holding – frass feeds the fungi and bacteria that create fluffy, well-aggregated soil.

• Eco-friendly & odour-free – produced from food-waste-fed larvae, it turns trash into garden treasure.

Pro Tip: Pair frass with a quality living-soil mix like TurboDirt for an instant biology boost.

How to Use Dr Greenthumbs Insect Frass

(1 heaped Tablespoon ≈ 3-4 g) 

Using insect frass for indoor plants

Insect frass works particularly well for indoor plants when used gently and consistently.

For potted plants:

• Apply a light top-dress (½–1 teaspoon for small pots, up to 1 tablespoon for large pots)
• Water in well to activate soil microbes
• Repeat every 4–6 weeks during active growth

Because frass supports microbial balance rather than forcing growth, it’s well suited to:

• Houseplants
• Herbs grown indoors
• Seedlings and young transplants

Many gardeners also find frass helpful when dealing with fungus gnats, as healthier soil biology makes conditions less favourable for larvae.

For best results indoors:

• Avoid over-application
• Ensure good drainage
• Let soil dry slightly between waterings

As with all organic inputs, less is more — frass works with your soil, not against it.

Frass for seedlings and transplants

Frass can be a handy little boost for seedlings and young transplants, but this is one place where more is definitely not better.

Young roots are sensitive. They don’t need a heavy feed dumped under them. They need a gentle biological nudge, good moisture, oxygen and low stress while they settle in.

For seedlings:

• Use a tiny amount mixed through the potting mix.
• Avoid piling frass directly against soft stems.
• Water in lightly after transplanting.
• Don’t combine it with a heap of other strong amendments.
• Wait until seedlings are actively growing before repeating.

For transplants, frass works best as part of the “settle-in” routine. Mix a small amount into the planting hole or top-dress lightly after planting, then water it in. The goal is to wake up biology around the root zone, not overload a young plant that’s already dealing with transplant shock.

If you’re building a biological starter mix, Dr Greenthumbs Insect Frass High Calcium & Chitin is the kind of input you use lightly and consistently, not by the handful.

Frass vs Worm Castings: The Quick Low-Down

If you want to see how worm castings perform on their own—and where frass outshines them—our Worm Castings Australia: The Complete Gardener’s Guide breaks down the biology, nutrient release and real-world results.

Step-by-Step Application

1. Top-dress & water – Sprinkle the recommended rate and water immediately to activate microbes.
2. Brew a frass tea – Soak 1 cup of frass in 10 L of de-chlorinated water for 24 h, then drench soil or foliar-spray. And if you're stacking this tea with other organic inputs, the Kelp Meal: Australia’s Ocean-Powered Fertiliser (2025 Guide) shows how kelp hormones pair with frass to supercharge stress resistance and growth.
3. Charge your compost – Add a handful per 20 L of compost to accelerate decomposition.

Insect frass tea: when it makes sense

Frass tea makes sense when you want to apply insect frass more evenly through soil, pots or garden beds without digging around the roots.

It’s not a magic potion, and it shouldn’t replace good soil structure, compost or proper feeding. But it can be useful when plants are already in place and you want a gentle biological drench.

Simple method:

1. Add frass to clean, dechlorinated water.
2. Stir well and let it steep for around 12–24 hours.
3. Stir again before applying.
4. Drench the soil around the root zone.
5. Strain well if using through a watering can rose, sprayer or irrigation gear.

Use frass tea fresh. Don’t leave a bucket sitting around for days until it smells rough. If it smells sour, anaerobic or rotten, tip it on the compost and start again.

The other mistake is using frass tea as a foliar spray without straining it properly. Fine particles can clog sprayers fast. For most home gardeners, soil drenching is simpler, cleaner and less annoying.

Frass in compost: a small boost that goes a long way

Frass is a ripper compost booster when used properly. It adds biology, a small nutrient kick and chitin-rich material that helps diversify what’s happening inside the pile.

You don’t need much. A light handful through a small compost bin or a thin sprinkle between layers is plenty. The compost still needs the basics: greens, browns, air and moisture. Frass just helps nudge the biology along.

Use it when your compost is:

• Slow but not rotten
• Mostly finished and needs a final biological charge
• Being used to build living soil
• Heavy on dry carbon and low on biological diversity

Don’t use frass to “fix” a stinking, wet compost pile. If the bin smells like a swamp, the issue is usually too much moisture, not enough air, or too many wet greens. Add dry carbon, turn it, and sort the structure first.

Frass works best in compost that’s already heading in the right direction. It’s an accelerator, not a rescue crew.

Using insect frass with other soil amendments

Insect frass can be used on its own, but it also works well when combined with other organic inputs.

Some gardeners choose frass blends that include:

• Biochar – for long-term carbon storage and microbial housing
• Compost or humus – to increase organic matter
• Mineral amendments – to balance trace elements

You can also create your own “stack” by:

• Applying frass first to activate microbes
• Following with compost or mulch to feed them
• Using biochar as a long-term soil structure addition

Straight frass is ideal when:

• You want a simple biological boost
• Soil biology needs rebuilding
• You’re working with living soil systems

Blended products can be useful where soil structure or carbon levels need extra support.

Composted vs fresh insect frass: what gardeners should know

Not all insect frass products are exactly the same.

Fresh frass straight from insect production can be high in moisture and biological activity, which is why most frass sold for home gardening is stabilised or composted before use.

This extra processing step:

• Reduces excess moisture and odour
• Improves consistency and shelf life
• Helps ensure the product is safe and stable for soil application

When choosing an insect frass product, it’s worth checking:

• That it’s intended for soil use, not raw waste material
• How it has been processed or stabilised
• Storage guidance (dry, sealed containers are ideal)
  

Well-processed insect frass should smell earthy, not sour, and feel crumbly rather than wet or sticky.

At home, store frass in a cool, dry spot and keep the lid sealed to protect the beneficial microbes until you’re ready to use it.

What research says about insect frass

Interest in insect frass as a soil input has grown significantly in recent years.

Research into insect-derived fertilisers shows frass can:

• Support microbial diversity in soil
• Contribute slow-release nutrients
• Provide chitin, which may help stimulate natural plant defence responses

Studies also highlight that outcomes depend on:

• How the frass is produced
• Application rates
• Existing soil conditions

This reinforces a key principle of organic gardening: biology first. Insect frass isn’t about quick fixes — it’s about building resilient soil systems that support long-term plant health.

Frequently Asked Questions

Is insect frass safe for edibles?

Absolutely. It’s an organic input and leaves no harmful residues.

Will frass attract pests?

No. In fact, the chitin helps plants deter sap-sucking insects.

For growers chasing an even stronger phosphorus and calcium boost—especially in fruiting crops—our Seabird Guano: The Ultimate Aussie Grower Guide 2025 explains how to integrate guano without upsetting soil balance.

Can I overdo it?

It’s pretty forgiving, but stick to the rates above—less is more thanks to the dense biology.

Ready to Super-Charge Your Soil?

Grab a bag of Dr Greenthumbs Insect Frass (High Calcium & Chitin) today and see the difference for yourself. Your tomatoes, chilies and citrus will thank you!

Happy growing from the team at Dr Greenthumbs—proudly helping Aussie gardeners cultivate thriving, chemical-free gardens since 2012.

Next reads for building stronger living soil

Want to get even more from insect frass? These guides will help you build soil biology, compare organic inputs and choose the right natural fertilisers.

• Worm Castings Australia Guide
• Natural Garden Fertilisers Australia Guide
• Organic Gardening 101: Living Soil Aussie Guide
• Seabird Guano Australia Guide

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