Pests- Fungus gnats

Identification: Adult fungus gnats are delicate in appearance. Often they can be seen running across or flying near the soil surface. They are weak flyers and are attracted to light.

The larvae are small worm-like creatures up to 1cm long with shiny black heads . If you look closely at the top of the soil you may notice tiny (almost transparent) larvae. It’s hard to spot them, though, as they tend to exist mostly under the soil.


Damage: The larvae generally feed on decaying organic material or fungi growing in the soil. The larvae of some species will also feed on roots. This feeding is especially damaging to very young plants. With older, established plants, the initial sign of an infestation is that the plant loses its normal healthy appearance.

Dry conditions- take soils out and let them almost dry out (until first signs of plant withering) and plug them in the garden again. Dry conditions will kill the larvae. It might be necessary to repeat the procedure couple of times to

Yellow sticky paper- helps to monitor and keep down the number of fungus gnat adults but it does not solve the issue entirely.

Biological control- Hypoaspis miles are a natural predators of fungus gnat purpae.

Hydrogen peroxide- mix one part of hydrogen peroxide (3%) with four parts of water and add it to the tops of all the soils. Be careful not to burn young plant roots with a mixture that’s too strong! It can also be added to a water tank to prevent mosquitoes.

Biological control- Hypoaspis miles are fungus gnat larvae natural enemies


Both of my mint plants have mold and as Iooked closer you see thin larvae type beasties. On one plant it was all through the plant, the second one I’m trying to salvage. I have noticed small black bugs around my plants and my arugula was brown a d dying. I did not get a photo of that. But I have attached photos from my mint plant. Should I be rotating the covers to prevent mold because my tomato plant has mold too but no beasties. I’d love it if someone has some thoughts because I am concerned I’m going to lose more plants. Thank you

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Sorry to see that fungus gants are taking over your garden @jan . Please follow the instructions above and hopefully you can find out what would work for you best.

Thank you so much. I actually had 3% hydrogen peroxide on hand. Do you know off hand how much I should add to tank too?

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@jan, same concentration. But I’m not sure about the effect once added to the water tank, since it also needs to go through the wick. Maybe @Maret can give some insight from her experience?

I would suggest to take plants out of the garden and let plant pods to dry (until you see first signs of plants withering) and then plug them in the garden again. Repeat once a week if necessary. It’s more effective than hydrogen peroxide as larvae cant survive in dry soil.

As an additional measure, make a hydrogen peroxide mixture in the water tank (one part of hydrogen peroxide (3%) with four parts of water). Stronger solution may burn young plant roots.

Here’s some tips - I am trying after discovering gnats buzzing around my C&G garden. I suspect the culprit was an invasion due to the mold developing from seeds I was attempting to sprout or a sickly mint plant from Trader Joe’s. So I discarded the seeds and TJ’s plants. Really love my C&G and want to keep it healthy and thriving.

  • Spray (mist bottle) 1:4 ratio of hydrogen peroxide in water. It kills the gnats on contact. And added some of it to the water tank & soil. Harmless to humans and plants.

  • Sprinkle cinnamon powder (anti-fungal) on the pods soil. Gnats hate dry soil. Sand is another alternative - among other things like diatomaceous earth - but I want to keep my system as non-toxic and clean as possible.

  • Place a little jar of apple cider vinegar or sweet wine (gnats love it) to attract gnats and put a lid with little holes (I used a dollar store shaker jar lid) to trap them inside.

  • Post it note (gnats love the color yellow) with Vaseline on it - as a fly trap… I put it on the backside of my C&G tank. So it is not unsightly… but paint stores have a variety of free yellow sample cards… so will see if brighter colors work better.

  • Some YT hacks swear by seeping the mosquito pellets in water… but I am not sure if that will be toxic? Anybody know about that?


Yellow post it note sticker with Vaseline - gnat flies trap - experiment.


Cinnamon powdered on the pod soil… to dry it out and as a natural anti-fugal protection.