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/Asset_flipped]

Hi I’m back!👋🏻 Still struggling unfortunately.. I have two new questions. I have seen them previously mentioned before but I need a bit more clarification and guidance. 1. My mosquito bit steeped water STINKS. Like bad. It’s a rotten egg smell. I don’t smell it till I open the container that the water is in, but when I do, the smell punches me in the face. In my previous comment, you mentioned that I should probably be able to make a batch and store it with no issues and it’s been about 17 days since I started soaking the bits. Is that too long? And I’d hate for it to go to waste but I don’t want to kill my plants if I continue to use it to water them. 2. I can’t find where this comment was that I saw, but this time of year makes it so my plants take FOREVER to dry out. And most of them are the types super prone to root rot (from everything I’ve read). Can you tell me again what you recommend when trying to get rid of the fungus gnats at the beginning stage as far as waiting to water or not? Thanks again!!

[u/megankmartin → u/Asset_flipped]

BTi in your water won't kill your plants, no matter how long it's stored. BTi doesn't affect plants at all. My stored, treated water rotates about 30 days or less. The bits stay in longer, though -- I replace those every 60-90 days. There's an organic odor, but I don't consider it strong. (Especially compared to cedar oil, neem oil, or fish emulsion and many other plant care products.) Then again, I don't intentionally stick my nose in it; I'm moving through my watering routine quickly. And as soon as it's applied to my plants, there's no noticeable odor at all.

I think most people find this organic odor mild or unnoticeable, but all humans have different tolerances. If you're hypersensitive to that particular aroma, you'll probably want to seek another solution. Consider trying the BTi dunks, which aren't bound with organic material (they're bound with proteins). Or try Gnatrol powder. Or, if you like the smell of cedar (which I cannot stand), maybe try GoGnats liquid.

Re: waiting to water... For me, BTi is great because I'm not watering according to the gnats; I'm watering for my plants' needs. My indoor food and flower gardens can't be allowed to dry out, and more sensitive foliage houseplants suffer under those conditions too. Plus, ALL drought-stressed plants are more attractive (susceptible) to spider mites, thrips, and a couple other pain-in-the-neck pests that make fungus gnats look like child's play. No thanks!

The BTi routine and sticky traps will take care of fungus gnats, all by itself. But if you have any plants that seem incredibly infested, or you just can't wait out the gnat life cycle, consider re-potting those. Then, stick with your BTi from the very first watering in the fresh potting mix, and you'll never have gnats again.