Mealworm Frass Fertiliser: Frequently Asked Questions

Mealworm frass is simple to use, but it is still a fertiliser—not a magic powder. This FAQ answers the most common questions about what it is, what is actually in RichRoots frass, how to use it, and what current research does and does not support.

Quick answers

• What is it? A dry, fine material produced during mealworm rearing, made primarily from mealworm excreta with small amounts of shed insect material and residual feed particles.
• Does it need composting? No. RichRoots is supplied for direct soil application at the rates we recommend.
• How do I apply it? Sprinkle it onto soil, lightly mix it into the surface where practical, then water as normal.
• How often? For actively growing plants, every 2–4 weeks is a useful starting point.
• Does it smell? Dry mealworm frass has a mild, earthy or grain-like smell rather than the strong odour associated with many fresh animal manures.
• Can I overapply it? Yes. Like any fertiliser, more is not automatically better. Use modest rates, especially around seedlings and sensitive plants.

1. What is mealworm frass?

Mealworm frass is produced by the larvae of Tenebrio molitor. In practical terms, it is the fine material left behind as mealworms eat and grow. It contains plant nutrients, carbon-rich organic matter and insect-derived compounds such as chitin.

Frass is a natural material, so its composition is not identical across every farm or every batch. Mealworm diet, rearing conditions and processing can all influence the final nutrient profile. That is why we prefer to publish the analysis of the actual RichRoots material rather than rely on a generic “frass NPK” number.

2. What nutrients are in RichRoots mealworm frass?

Our current independent analysis found the following:

It also contains naturally occurring trace elements. Because frass is a natural product, results can vary somewhat between batches.

3. How do I use mealworm frass?

For ordinary home-garden use, our recommended method is deliberately simple: apply a modest amount to the soil, lightly incorporate it into the surface where practical, and water it in.

Our step-by-step mealworm frass application guide gives starting quantities for small, medium and large pots, garden beds and new plantings.

For seedlings, newly established plants and plants already under stress, start lightly and observe the response before increasing the amount.

4. Can mealworm frass burn plants?

We do not describe any fertiliser as impossible to overapply. Mealworm frass is often used at relatively modest nutrient concentrations compared with concentrated mineral fertilisers, but dose, plant species, pot volume, soil condition and growing environment still matter.

The practical approach is to follow sensible application rates rather than assume that an unlimited amount is harmless. This is especially important in small pots and around young or sensitive plants.

5. Is mealworm frass suitable for every plant?

It can be used across many common garden and container plants, but plants do not all have the same nutrient requirements. Species adapted to very nutrient-poor conditions, specialised growing media or unusual pH regimes may need different treatment.

If you are growing carnivorous plants, highly sensitive seedlings, orchids in specialised media, hydroponic crops or another system with tightly controlled nutrition, do not assume the standard soil rates apply.

6. What about microbes and chitin?

Mealworm frass contains insect-derived organic matter and chitin, and research has found that frass can influence soil microbial activity and plant responses. However, the mechanism is more nuanced than saying that every handful contains a guaranteed population of “beneficial microbes” that will produce the same result in every garden.

For example, a 2023 mealworm-frass study found that the frass microbiota was not required for the fertilising effect observed in that experiment. The same study found a systemic defence response against Botrytis cinerea under controlled conditions, while a local root defence response was not detected. These are interesting findings, but they are not a guarantee of pest or disease protection in a home garden.

For a deeper review, see The Science Behind Mealworm Frass Fertiliser.

7. Does RichRoots frass need to be composted first?

No. For the soil applications described on our site, RichRoots is supplied for direct use. You do not need to compost or “age” it before applying it at the recommended rates.

8. Does mealworm frass smell?

Dry mealworm frass generally has a mild scent closer to grain or soil than fresh animal manure. Once it is incorporated into soil and watered in, the smell is usually unobtrusive.

9. What size should I buy?

For repeated feeding across several plants, veggie beds or larger pots, the 360g Large Garden Pouch is our main garden-size option.

Shop the 360g Large Garden Pouch →

More useful guides

For practical rates, read How to Use Mealworm Frass Fertiliser on Plants. For the broader soil-health story, read Why Frass Fertiliser is the Future of Soil Health. Delivery and returns information is available on our Delivery, Shipping & Returns page.

Selected research

1. Houben, D. et al. (2020). Potential use of mealworm frass as a fertilizer: Impact on crop growth and soil properties. Scientific Reports. doi:10.1038/s41598-020-61765-x
2. Blakstad, A. et al. (2023). Frass from yellow mealworm (Tenebrio molitor) as plant fertilizer and defense priming agent. Biocatalysis and Agricultural Biotechnology. doi:10.1016/j.bcab.2023.102862
3. Amorim, H. C. S. et al. (2024). Insect frass composition and potential use as an organic fertilizer in circular economies. Journal of Economic Entomology. doi:10.1093/jee/toad234