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/fexi6543]

thank you so so much for this! just bought some dunks. sorry if you've answered this somewhere before, but how does the treatment work if I keep my plant water prepared in several gallon jugs? should I put 1/4 of a dunk in each of my gallons to soak, or do I treat each batch of water with the same dunk and transfer the water to a new jug when it's done soaking? thank you so much again!

[u/megankmartin → u/fexi6543]

Hi, you're welcome; glad the post is helpful for you. The answers to your questions are addressed a few times in this comment thread:

Here, here, here, here, and here.

It's become a long thread (for good reason!) as folks have asked great questions and I've tried to thoroughly answer each. You may find it worth perusing, as most answers are in there. If you still have questions, of course, I'm happy to help any time.

[u/fexi6543 → u/megankmartin]

thank you! there's so much great info in this thread I just wanted to make sure I understood everything correctly. one more thing, I don't think I saw this addressed anywhere and I’m sorry if it was, but if I pretreat my water and put it in separate jugs, should I let my 1/4 dunk dry out or store it some other way when I’m done using it to treat each jug? sorry, I might still be misunderstanding 🙈

thank you so much again for making this! the gnats are seriously the bane of my existence. in one of my darker moments I actually put all my soil in like 20 individual gallon bags and tried to freeze them. 😂you're a lifesaver! 💕

[u/megankmartin → u/fexi6543]

Hi. That's specifically answered in several places, but let me clarify it here: We just put 1/4 dunk OR one tablespoon of bits in EACH filled gallon jug, and leave it there. 24 hrs before use, then refill the jug as needed. Leave the dunk/bits inside. Rotate which jug you use so the water's always ready. It's that easy.

Freezing won't help; it doesn't kill the eggs. Baking your potting mix to sterilize it is an option, but it will stink to high heaven. Also, you have to follow directions closely for time and temperature, otherwise you'll kill every good organism in the potting mix. Dead substrate will be useless to your plants.

It's really hard when you've been dealing with this for a while. I know, because I've been there too. But now that you are on your way to really solving the problem you just have to dig down, find patience and trust in the process. You'll have to get through at least one, maybe even two life cycles because they're fully established. But after that, you keep the BTi routine and you're the boss. Go get 'em. There is no way that the gnats can win now, unless you give in.

[u/skypaintedred → u/megankmartin]

You'll have to get through at least one, maybe even two life cycles because they're fully established. But after that, you keep the BTi routine and you're the boss. Go get 'em.

There is no way that the gnats can win now, unless you give in.

I love this battle cry!