Do Gnats Like Cinnamon? And How to Actually Get Rid of Them

Gnats do not appear to be attracted to cinnamon, and there is some indirect reason to think it could discourage them, but the evidence is far weaker than the internet suggests. No published study has directly tested cinnamon as a gnat repellent. The connection between cinnamon and gnat control rests almost entirely on cinnamon’s well-documented antifungal properties, which could, in theory, reduce what draws certain gnats to your houseplant soil in the first place. That theoretical link has taken on a life of its own in gardening forums and home-remedy listicles, to the point where “sprinkle cinnamon on your soil” has become standard advice despite never being validated in a controlled experiment on actual gnat behavior.

Why Cinnamon Keeps Coming Up

The gnats most people deal with indoors are fungus gnats, small dark flies in the family Sciaridae. The adults are the ones you see hovering around your face and your plants, but the real action happens underground. Female fungus gnats lay eggs in moist soil, and the larvae feed primarily on fungi, decaying organic matter, and sometimes plant roots. That fungal food source is the key to why cinnamon enters the conversation at all.

Cinnamon and its chemical compounds, particularly cinnamaldehyde, have genuine antifungal activity. Research has confirmed that cinnamon bark extract can significantly inhibit the growth of plant-pathogenic fungi, with higher concentrations causing visible deformation of fungal structures and substantially reducing fungal colonization of growth media.¹ A broader review of cinnamon’s bioactive properties concluded that it effectively hinders both bacterial and fungal growth, and noted its potential phytotoxic effects on plants at higher doses.²

The reasoning goes like this: if cinnamon suppresses fungi in the soil, and fungus gnat larvae depend on fungi for food, then cinnamon should make the soil less hospitable for gnat larvae, eventually reducing the adult population. It is a plausible chain of logic. The problem is that each link in the chain involves assumptions that have not been tested together. The antifungal concentrations shown to work in lab settings involve standardized extracts at specific percentages mixed into growth media, not a dusting of grocery-store cinnamon powder on the surface of a potted plant. And even if the cinnamon did suppress soil fungi, nobody has measured whether the reduction would be enough to meaningfully starve out gnat larvae, which also feed on decaying organic matter and roots.

The Gap Between Antifungal and Anti-Gnat

This distinction matters more than most advice articles let on. Showing that a substance kills fungi in a petri dish is not the same as showing it controls an insect population in a pot of soil. Fungus gnat larvae are not obligate fungivores in the strictest sense: while fungi are their primary food, they are opportunistic feeders. Larvae will consume decomposing plant material, algae, and fine root hairs when fungal resources are limited. Eliminating fungi from the top layer of soil, even if cinnamon could do that reliably, does not necessarily eliminate the larvae’s food supply deeper in the pot.

There is also the question of dose. The antifungal studies that show strong results use cinnamon bark extract at concentrations of 3 to 5 percent mixed into the growth medium, and even then, the effect scales sharply with concentration: one study found a threefold difference in fungal inhibition between 3 and 5 percent extract.¹ A light sprinkling of cinnamon powder on the soil surface is not remotely comparable to a 5 percent extract solution mixed uniformly into the medium. The active compound, cinnamaldehyde, needs to come into contact with the fungal organisms to inhibit them, and surface application does not penetrate well into moist, organic-rich potting soil.

None of this means cinnamon is useless. If you already have your gnats mostly under control and want to sprinkle some cinnamon on the soil surface as a supplementary measure, it probably does no harm and may offer a mild antifungal benefit in the top layer. But treating it as a standalone gnat solution is setting yourself up for disappointment.

A Caution About Cinnamon and Your Plants

The same review that praised cinnamon’s antifungal properties also flagged its phytotoxic potential.² Phytotoxicity means harm to the plant itself. At the concentrations needed to reliably suppress fungi, cinnamon compounds can damage plant tissue. This is why some researchers have explored cinnamon as a potential herbicide, not just a fungicide. If you are dumping large amounts of cinnamon onto your houseplant soil in hopes of killing gnats, you could end up stressing the plant, which would be counterproductive since weakened roots are more susceptible to feeding damage from gnat larvae. A thin dusting is unlikely to hurt most established plants, but heavy or repeated application deserves caution, especially with seedlings or sensitive species.

What Fungus Gnats Are Actually Drawn To

Understanding what attracts fungus gnats is more useful than trying to find something they dislike. Their life cycle revolves around moisture and organic decay. Adult females seek out moist soil rich in organic material for egg-laying. Overwatered houseplants with soggy, peat-heavy potting mix are ideal nurseries. The adults themselves are strongly attracted to light, a trait researchers have confirmed in controlled experiments: when given a choice, fungus gnats consistently move toward brighter light sources, with a higher percentage captured on traps positioned near directional light compared to those farther away.³

The adults are also drawn to the carbon dioxide and volatile organic compounds released by decomposing matter and fungal growth in soil. This is why the gnats cluster around your plants and not, say, your bookshelf. They are following chemical cues that tell them a suitable egg-laying site is nearby. Controlling those cues through soil management is far more effective than trying to mask them with cinnamon.

Watering Habits Are the Single Best Fix

The most effective thing you can do about fungus gnats costs nothing and requires no product. Let the top inch or two of your potting soil dry out completely between waterings. Fungus gnat eggs and early-stage larvae need consistent moisture to survive. If the upper layer of soil dries out regularly, eggs desiccate before hatching and young larvae die before they can burrow deeper. This alone can break the reproductive cycle within a few weeks for most houseplant situations.

Bottom watering, where you fill a saucer or tray and let the plant absorb water upward through drainage holes, keeps the soil surface drier while still hydrating roots. It is a practical change that directly addresses the gnats’ egg-laying preferences without any additional products. Combined with well-draining potting mixes that do not stay waterlogged, soil moisture control is the foundation that every other gnat-control method builds on.

Soil Amendments That Actually Have Data Behind Them

If you want to change the growing medium itself to discourage gnats, there are options with stronger evidence than cinnamon. Research on amending potting soil with black soldier fly byproducts found dramatic reductions in fungus gnat populations. Adding a mixture of byproducts to standard potting soil reduced the gnat population by about 93 percent compared to unamended commercial potting soil, while frass (insect waste) amendments reduced populations by 77 to 80 percent.⁴ Part of the effect came from adult females simply preferring not to lay eggs in the amended soil, suggesting the substrate itself was a deterrent to oviposition.

Black soldier fly frass is commercially available as a soil amendment and fertilizer, which makes this finding practically relevant if you are a greenhouse grower or a serious indoor gardener. For the average person with a few houseplants, though, sourcing and using these products may feel like overkill. The more accessible takeaway is that the composition of your potting mix matters. Dense, peat-heavy mixes that stay wet for days are gnat magnets. Adding perlite, coarse sand, or other inorganic components to improve drainage and reduce the organic richness of the surface layer makes the soil less attractive to egg-laying females.

One popular suggestion that falls flat in the evidence is diatomaceous earth. Research that tested adding diatomaceous earth directly into the growing medium found that it did not improve control of fungus gnat larvae at the concentrations tested, leading researchers to conclude it may not be beneficial for greenhouse producers dealing with this pest.⁵ A thin layer on the soil surface might deter adult egg-laying by creating a dry physical barrier, but that effect has not been convincingly demonstrated either.

Trapping the Adults

While soil management targets the larvae and egg-laying cycle, trapping deals with the adults you are already seeing. Yellow sticky traps are the standard. They exploit the strong visual attraction fungus gnats have to the yellow-green part of the spectrum. Placing them near the soil surface of infested plants can capture large numbers of adults before they lay eggs.

Adding light to those traps makes them work even better. Yellow sticky cards equipped with light-emitting diodes captured more fungus gnats over a 24-week test than identical yellow cards without LEDs.⁶ More detailed work on which wavelengths are most effective found that UV light around 382 nanometers was the strongest attractor, followed by green-yellow light in the 532 to 592 nanometer range. Combining UV and yellow LEDs on the same trap improved capture rates compared to either wavelength alone, and also outperformed plain yellow sticky traps.⁷ You can find small UV-equipped sticky traps marketed specifically for houseplant gnats now, and the research supports the idea that they genuinely improve on passive yellow cards.

Apple cider vinegar traps are another common recommendation. Research on fruit flies (Drosophila species) has confirmed that fermentation products like acetic acid, ethanol, and ethyl acetate are attractive to these insects, and that apple cider vinegar serves as an effective base attractant in trap designs.⁸ The catch is that this research focused on Drosophila, not Sciaridae. Fungus gnats and fruit flies are different insects with different ecological niches. A vinegar trap in your kitchen will catch fruit flies reliably, but it is less effective against fungus gnats, which are not strongly attracted to fermentation odors. If you have both types of gnats, a vinegar trap handles one and sticky cards near your plants handle the other.

How to Tell Which Gnat You Have

This is worth pausing on because “gnat” is an imprecise term that covers several distinct insects, and the right control strategy depends on which one is in your house. Fungus gnats are dark-bodied, delicate, and tend to hover near soil or fly weakly in zigzag patterns around plants. They are not interested in your fruit bowl. Fruit flies (Drosophila) are tan or brownish, slightly more robust, and gather around overripe fruit, drains, and anything fermenting. Drain flies (Psychodidae) are fuzzy and moth-like, and they breed in the organic buildup inside drains and pipes.

The vinegar trap that works beautifully for fruit flies does almost nothing for fungus gnats. The sticky card near your houseplant that catches fungus gnats will not solve a drain fly problem in your bathroom. And cinnamon, even if it worked as advertised, would only be relevant to fungus gnats through its soil-fungus connection. Identifying which insect you are dealing with is the first step that many advice articles skip, and getting it wrong means wasting time on the wrong remedy.

Why Essential Oil Remedies Tend to Fade

Beyond cinnamon, you will find recommendations for using other essential oils to repel gnats: peppermint, lemongrass, clove, and neem oil among them. Some of these do contain compounds with documented insecticidal or repellent properties. But there is a practical problem that rarely gets mentioned in the home-remedy world: insects can habituate to them.

Research on how insects respond to repeated exposure to essential oils found that larvae raised in the presence of lemongrass and clove bud oils developed gustatory habituation, meaning they became desensitized and the oils lost their deterrent effect over time. The reduction in feeding deterrence correlated directly with repeated exposure and measurable desensitization of the insects’ sensory organs.⁹ That study focused on caterpillars rather than gnats, so the specific findings do not transfer directly. But the principle of habituation is well established across insect groups. An essential oil that seems to work for a week or two may gradually lose effectiveness as surviving insects or new generations become less responsive to it. This is a real limitation of essential-oil-based pest control that synthetic pesticides were specifically designed to overcome.

Interestingly, not all oils behaved the same way. Fennel sweet oil did not produce habituation in the same study, suggesting that different chemical compounds interact with insect sensory systems in fundamentally different ways.⁹ The research on which specific compounds resist habituation is still early. For now, if you are using essential oils as part of your gnat control, rotating between different oils rather than relying on one continuously is the more defensible approach, though even that is an extrapolation rather than a tested protocol.

A Practical Layered Approach

If you are dealing with an active gnat infestation in your home, the combination that has the most support looks like this:

• Dry out the soil: Let the top layer of potting mix dry completely between waterings, and switch to bottom watering where possible. This disrupts the egg-to-larva cycle at its most vulnerable point.
• Trap the adults: Place yellow sticky cards at soil level near affected plants. If the problem is severe, consider UV-equipped traps for improved capture rates.
• Improve your potting mix: Repot with a well-draining mix that includes perlite or coarse grit. Avoid pure peat-based mixes that hold moisture near the surface for days.
• Check other moisture sources: Overwatered saucers, leaky trays, and damp organic debris under pots all provide habitat. Empty saucers after watering and clean up fallen leaves.

Cinnamon, if you want to use it, fits as a supplementary surface treatment after the fundamentals are in place. A light dusting on dry soil may offer modest antifungal benefit and is unlikely to harm established plants. Treating it as your primary weapon, though, is relying on the weakest link in the chain while ignoring the interventions that address the gnats’ actual biology.

When Gnats Persist Despite Everything

Sometimes the problem is not your care routine but your potting soil itself. Bags of potting mix can come pre-infested with fungus gnat eggs or larvae, especially if they have been stored in warm, humid conditions. If you repot a plant into fresh soil and gnats appear within a week or two despite careful watering, the soil was likely the source. Some growers microwave or bake small batches of potting soil before use to sterilize it, though this is impractical at scale and produces a memorable smell. A more common approach is to store new bags of potting mix in a sealed container and inspect them before use, discarding any bags that show signs of excessive moisture or fungal growth.

Persistent infestations in greenhouses or large plant collections sometimes call for biological controls like Bacillus thuringiensis var. israelensis (Bti), a naturally occurring soil bacterium that is toxic to fly larvae but harmless to plants, people, and pets. It is sold as a liquid or granular product and applied as a soil drench. Predatory soil mites, particularly Hypoaspis miles (now called Stratiolaelaps scimitus), are another biological option used in professional settings. These tiny mites live in the top layer of soil and feed on fungus gnat larvae and eggs. Neither of these requires a chemistry degree to use, but they do require a bit more commitment than sticking a yellow card in a pot. For most houseplant owners, the combination of watering discipline and sticky traps handles the problem without needing to escalate to biologicals.