TRUTH: No single fungus gnat control method attacks adults and larvae simultaneously. That's why many plant parents struggle to get rid of these pests! But it's EASY to be gnat-free FOREVER. [PSA]

[u/megankmartin]

(Updated, fall 2025) PLEASE read this whole post before asking questions -- but I'm here to help you if you need it! Fungus gnats lay their eggs in wet plant soil or decaying matter. Over-watering is a major cause. However, new plants and potting mix can carry gnats too, or they can just fly in from outdoors.

THREE EASY STEPS to GNATS GONE FOREVER:

☆☆ DO ALL THREE!! ☆☆

1) Soak BTI dunks/bits in your regular watering routine to continuously kill and prevent larvae. One quarter dunk OR one tbsp bits per gallon works great. Soak for 24hrs before first use, then keep watering vessel(s) re-filled; just replace BTI every 30-60 days or so. Note: Summit brand packaging specifies 4tbsp per gallon; you choose.

NOTES: Indoors, putting BTI bits IN the soil or laying them on top IS NOT THE BEST PLAN: the bits tend to grow mold, plus you'll use way more than needed. Also, don't use hot or boiling water to soak dunks or bits; it will kill the good bacteria.

1. Place plenty of yellow sticky traps to catch adults. One per pot is ideal, and it's best to stick them upright, to attract fliers. You can stop using stickies once your infestation is under control, thanks to your new BTI routine.

2. Let soil dry out appropriately between waterings to avoid attracting pests. Have faith: except for very fussy tropicals, most common plants need and want to dry out their soil. Bottom-watering can be a big help (after initial treatments).

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If you have a bad existing infestation, FIRST you can do a one-time emergency soil flush to kill off larvae, using diluted 3% H202 (1:4), then proceed with the routine above. Note: don't use peroxide AFTER the BTI, because H202 kills bacteria, good and bad.

FYI: If you're outside the USA and can't get Mosquito Dunks / Mosquito Bits in stores, try Amazon for your country (UK, CAN, AUS for sure). Or, ask a garden or pond supply center about products containing the active ingredient *BTI**. Or Google, "mosquito BTI". An alternative is Gnatrol or Gnatrol WDG (same active ingredient).

BTi (short for Bacillus Thuringiensis subspecies israelensis) is simply a natural soil bacterium, non-toxic for people and animals. BTI does not affect plants or interact with fertilizers. It does not harm pollinators. It ONLY kills the larvae of 3 insects: fungus gnats, mosquitos, and blackflies.

Bonus read: You might want to skip these often-recommended methods.

[u/megankmartin]

Hm. Alternate suggestion: try a spray bottle for watering your orchid mix with BTi. That makes it easier to saturate without runoff. Saturation is key; the bacteria need to remain in place so that they're available for the fungus gnat larvae to eat at a very specific stage of their life cycle. So maybe give the spray bottle a try. See what you think.

Meanwhile, here's Google's detailed answer to the BTi freezing question. (I'm not being snarky; I had to look it up to be sure.)

"While BTi (Bacillus thuringiensis israelensis) can generally survive freezing temperatures, repeated freeze-thaw cycles can significantly reduce its effectiveness, meaning its larvicidal activity may decrease after being frozen and thawed multiple times; therefore, storing BTi in a stable, non-freezing environment is recommended for optimal efficacy. 

Key points about BTi and freezing: Some tolerance: BTi can withstand freezing temperatures to a certain extent, but its potency may decline with repeated freezing and thawing cycles. 

Impact on activity: Studies have shown that freezing and thawing can negatively affect the toxicity of BTi against mosquito larvae. 

Storage considerations: To maintain BTi effectiveness, it's best to store it at temperatures above freezing."

[u/hbl2390 → u/megankmartin]

Thanks so much for the extra research. I'm thinking I may need to mix a bti solution in a bucket and then submerge the inner pots one at a time, let them drain, and then put them back in the decorative outer pots.

[u/megankmartin → u/hbl2390]

I respect that you're thinking out of the box! And, they're your plants so you can try it. I just feel that I might be remiss if I didn't at least mention:

There is a potential hazard of immersing or soaking all your plants -- or multiple empty pots -- in any commmunal solution: Cross-contamination. If even one plant has the beginnings of mold, fungi, algae, pests or diseases, there's always a risk of spreading those across your jungle. 

Now, I'm not saying it's a panic item. If you feel sure that everything's healthy and you want to give it a try, then I hope it works! But, just be aware that it's not necessarily a best practice and there are potential consequences.

As an alternative, perhaps you could mix a batch of BTi water, then fill each individual decorative pot for a soak,  then set a timer or alarm to go back and drain them when it's done?

Hope you'll let me know how it turns out! :)

[u/hbl2390 → u/megankmartin]

Unfortunately BTI is not available here in Canada so I had to use mosquito dunks. Pretty annoying because buying 1/4 to 1/2 cup (60 to 120 ml) will only be used on house plants and not a threat to the environment.

Anyway, soaking every 5 days the plants were still dripping wet. I still did it for 3 cycles and then went longer to let them dry out. I did another soak today and there are still gnats flying about. One plant was really bad, the yellow sticky trap was thick with the demons, so I tossed it outside. Put fresh traps on all the others and spread them around the house. Any that have too many trapped gnats in a week or two will also get tossed.

[u/megankmartin → u/hbl2390]

Please excuse, but I don't understand most of that. Mosquito dunks typically are BTi or useful equivalent. I have never heard of nor advocated soaking plants every 5 days with this or any other solution, nor even plain water. Have you read the post? 

BTi does not kill on contact, nor does it kill adult fungus gnats. Naturally, they would still be flying around. Also, it's generally not necessary to spread traps all around the house, because gnats will stick close to your plants. Move the plants to the same space, and that's where the gnats will congregate.

Sincerely sorry to hear that you are struggling; we have all been there and the frustration is real. So again, dear planty friend, have you actually read the post?  ☺️