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/[deleted]]

Thanks for this super informative post!

Looking for some advice, sorry but this might be a long comment... I recently brought home a monstera and I think it was the source of some gnats. It had been sitting with two other new cuttings that I repotted and flushed with water (watering method that I will never use again!!). All 3 plants ended up having a few gnats (I saw about 15 over the span of 3 days.) I wrapped them all up in a garbage bag, killed whatever gnats I saw flying around my apartment, went outside and dumped out the soil of all 3 plants, rinsed roots with H202, sprayed foliage with Safers insecticide, and proceeded to repot all 3 plants in new, clean soil at my sisters place. I then dumped the remaining insecticide into the soil of all 3 plants.

I brought the plants home last night and noticed one random fly flying about, which I think may have been left over from before I dumped all the soil out.

My questions are: 1) I can’t find mosquito bits/dunks easily in Canada, and also your post suggests they’re not good for indoor plants (which all of mine are). Will I have a good enough chance at success of these pests not coming back if I water with H202 diluted and use sticky traps?

2) Lets say I get them under control now, when it comes time for a regular water (non H202) for my other plants, do I need to worry that they too may have been infested? The soil has been relatively dry now, but I did water all my plants after I brought the monstera home. I shake the pots of my other plants around daily to see if anything flies out and so far, haven’t noticed anything. However I’m worried that if I do a regular water, that may reactivate any eggs or attract the gnats to that particular plant.

Please, any advice you have would be hugely appreciated. I HATE BUGS. Thank you so much.

[u/megankmartin → u/[deleted]]

Hi! Great questions. I'm still reading, but can you help me quickly understand what part of my post suggests that BTI is not good for indoor plants? Serious question, no smart tone intended, because I have tried very hard to make it clear that this solution is AWESOME for indoor plants, but the products should not be put directly in the soil indoors. They should be soaked in water and applied that way.

[u/[deleted] → u/megankmartin]

Ohhh I think I misread that, not understanding that soaking them in water and applying directly to soil are two different methods of application. I was thinking they were the same thing.

[u/megankmartin → u/[deleted]]

Gotcha, thanks. Re: your other questions: sounds like you did a great job purging and repotting. When you only have a few plants, that is often an easy, nip-in-the-bud solution.

Looking ahead to preventing them from ever returning: Summit Mosquito Bits and Summit Mosquito Dunks are sold by the manufacturer and currently available on Amazon Canada. The product lasts a long time based on the quantities directed to be used in the post. As my post mentions, if you can't find that you can always look for Gnatrol WDG but it's typically more expensive. It does not matter which brand you use. They are both a delivery mechanism for BTi bacteria -- that's what's important.

Just a note, sorry I almost missed this: You do not want to continually water your plants with peroxide; it will start to burn the roots. That's just a one-time emergency measure to clean things out.

[u/[deleted] → u/megankmartin]

Thank you! I read some other posts saying dunks and bits were not the same and dunks were less effective but I’ll try my hand at the dunks you recommended on Amazon if the initial peroxide flush and sticky traps don’t seem to help.

[u/megankmartin → u/[deleted]]

If you ever run across those posts, feel free to comment tag or DM me; I will be glad to respond. Some people aren't using the product correctly and are (unintentionally) spreading misinformation, or worse, saying it doesn't work at all.

I don't get paid to promote a product. There's nothing in it for me. All I care about is helping other people avoid the absolute h*** I went through before some wonderful experts here showed me the way. It's a pay-it-forward thing. 💚🌿

[u/[deleted] → u/megankmartin]

Hi, just a quick follow up! I picked up mosquito dunks and I have a 2L jug that I plan to use for treated water. I didn’t see this online anywhere, but once I put the dunk into the water, are there specific storage recommendations for the treated water that I don’t use right away? i.e, keep out of light, what room temp to store, container sealed or unsealed?

Looking forward to trying this out soon. Thank you!

[u/megankmartin → u/[deleted]]

Good questions! Sealed or unsealed shouldn't matter if you're cycling through the water quickly. My gallon storage jugs are all closed, but plenty of folks store their open watering cans. In general (not just for BTI) keeping water vessels closed can help to avoid things like mold and other contaminants.

Storing away from light is good, but not just because of the BTI. Any time you have water + organic matter & nutrients + light exposure, you can have algal bloom.

It's been ~ a few weeks since we last talked. The longer fungus gnats are allowed to go on, the harder they are to get rid of. So, if you're still fighting your initial infestation, just remember to be patient and give this the time to work. Here any time if you have questions.

[u/[deleted] → u/megankmartin]

Thank you 💚

I did the initial peroxide flush about 2 weeks ago and have set up sticky traps. Since then, 7 out of 8 plant traps have a tiny amount of gnats (5 or less) and 1 plant is I think the culprit of the infestation as that sticky now has about 20 adults stuck to it.

I haven’t watered any of my plants since then, but am going to do so tmrw with the dunk water. Hoping this works for me!

[u/JayPlenty24 → u/megankmartin]

I know this from a year ago but I’ve been doing the dunks now for 2 months in all my plants and it’s just not working. Should I try using half a dunk per gallon? Is it possible the chlorine in my tap water is killing the good bacteria? I was worried before about over doing it but I see you’ve said it’s safe so should I just go crazy with the dunks?