Insect frass fertiliser in the UK: what it is, what it does, and how to use it

If you’ve been gardening for any length of time, you’ll have noticed a pattern: most “quick-fix” feeds can give a burst of growth, but they don’t always leave your soil in better shape. That’s why more UK gardeners are looking for natural fertilisers that work with the soil, not against it.

One option you’ll see mentioned more and more is insect frass fertiliser. It’s simple, surprisingly tidy, and (when it’s produced well) very consistent to use. This guide covers what frass is, how it works, and the practical ways to apply it around the garden and indoors.

What is insect frass?

“Insect frass” is the natural material left behind when insects are reared and fed. In plain terms, it’s a blend of insect droppings and other fine organic material from the rearing process.

Frass is used as a soil-friendly fertiliser because it adds organic matter and plant nutrients in a way that tends to be gentler than many synthetic feeds. It’s also easy to handle compared with some traditional organic fertilisers.

Is frass the same as “insect poo”?

Gardeners often call frass “insect poo” because that’s the easiest shorthand — but frass is usually a bit more than that.

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

• insect droppings
• tiny fragments of shed skins (a natural part of insect growth)
• small amounts of leftover feed material broken down into fine particles

What matters for you as a gardener is that it’s a stable, usable soil input that’s straightforward to apply and store.

What does insect frass do for plants?

Insect frass is typically used for three reasons:

It feeds plants more gently than “blast” fertilisers

Frass is commonly chosen when you want steady support rather than forcing fast, soft growth. Gardeners often use it to keep plants ticking along in a more balanced way, especially where the soil is already reasonably healthy.

It supports soil health, not just top growth

Many natural fertilisers focus on providing nutrients. Frass is also valued for the way it contributes organic matter, which helps with the overall functioning of soil — the bit that ultimately makes feeding more efficient.

It’s practical, clean, and consistent

For people who dislike the mess (or smell) of some traditional organics, frass can be a genuinely pleasant alternative: easy to sprinkle, easy to measure, and easy to store.

Frass vs compost, manure and liquid feeds

Frass isn’t a replacement for everything — it’s best thought of as one tool in a sensible soil routine.

• Compost is brilliant for improving soil structure and long-term fertility, but it isn’t always strong or consistent as a fertiliser on its own.
• Manure-based products can be effective, but they vary a lot in strength and can be heavier to handle.
• Liquid feeds (like seaweed) are useful for targeted support, especially in containers, but they don’t do the same job as adding a dry soil input.

Frass tends to sit in the “steady, practical, soil-friendly” middle ground — particularly handy for pots, beds, and general maintenance feeding.

How to use insect frass fertiliser

The safest rule with any concentrated natural fertiliser is: start modestly and build from there, especially with houseplants and young seedlings.

Here are the most common ways UK gardeners apply frass:

1) Mix it into compost or soil before planting

If you’re preparing pots, grow bags, or a new bed, frass can be mixed through the top layer of compost or soil. This is often the easiest way to spread it evenly.

2) Top-dress established plants

For established plants (houseplants, borders, veg beds), you can sprinkle a light layer around the base of the plant and gently work it into the surface. Water afterwards so it settles in.

3) Use it as part of a routine, not a rescue remedy

Frass is usually most useful as a regular, measured input. If a plant is already struggling badly (poor drainage, root issues, severe nutrient deficiency), feeding alone won’t fix the underlying problem — so it’s worth addressing conditions first.

Tip: If you’re using frass indoors, apply lightly and keep it off leaves and stems. Wash hands after use and avoid creating dust when pouring.

When should you apply frass in the UK?

For outdoor plants, feeding is generally most relevant during active growth. In the UK that usually means spring through summer, sometimes into early autumn depending on what you’re growing.

For houseplants, “season” matters less than light levels. Many indoor plants slow down in winter because of low light, so feeding is often reduced or paused — even if the home is warm.

Choosing a frass fertiliser you can trust

Because “frass” is a category, quality can vary. If you’re comparing options, look for:

• clear provenance (who produces it and how)
• a product that feels dry and stable, not damp or clumpy
• consistency from bag to bag (important if you’re relying on repeatable results)
• sensible guidance on how to apply it

Flytiliser: frass for home gardens and bulk use

If you want to try insect frass at home or in a typical UK garden, Flytiliser is available as a smaller format that suits pots, beds and borders: Flytiliser insect frass fertiliser (500g) is here: https://syntects.co.uk/product/flytiliser

For growers, landscapers, and larger sites, there’s also a bulk option: Flytiliser insect frass fertiliser (1 ton) is here: https://syntects.co.uk/product/flytiliser-insect-frass-fertiliser-1-ton

The bottom line

Insect frass fertiliser is popular for a reason: it’s a practical, soil-friendly way to support plant growth without the heavy-handed feel of some feeds. Used sensibly, it’s an easy addition to a routine that prioritises healthier soil and more resilient plants.