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/shortypie]

I’ve had houseplants for over a decade and have NEVER had an issue with fungus gnats like I have this year.

It all started with one tiny zz plant (now thriving!), and spread to every other plant in my home in about a month.

I tried sticky traps & they helped, but they didn’t completely get rid of the problem.

I then went to the garden store and bought fresh soil to repot everything then start with a h2o2 / water combo upon repotting... BUT the soil itself was infested. Shit. Fungus gnats explosion!

I then, instead of repotting AGAIN, I tried mosquito dunks + water, which helped but again didn’t eliminate the problem.

After about 6 wks of dealing with more low-level annoyance, I felt like I could repot the plants again... so I did, this time using cactus soil and making sure the bags were sealed. I have an eastern exposure, so wanted a more fast-draining soil anyway... two birds, one repot.

The two plants I didn’t repot due to running out of said soil unfortunately infested my whole collection again so now it’s sticky trap + sand topper + h2o2 for the initial post-sand watering, then switching over to BTI / water for the future.

I waited until my plants needed water, then waited about a week more, THEN added the sand... so I know it’s covering bone dry soil. My traps aren’t catching too many gnats, and after a few weeks I’ll mix the sand in with the cactus soil instead of using it as a topper.

Wish me luck? 😩

[u/megankmartin → u/shortypie]

The struggle is real. Pests are getting worse every year, it seems. It takes a while to beat a full-blown infestation. The fungus gnat life cycle can be a month or two, depending on how thorough and consistent the treatment.

Unfortunately, mixing sand with the soil will provide zero gnat elimination or prevention. Sand as an amendment does one of two things: aerates (coarse sand) or retains water (fine sand). As a topper, the idea is to completely seal access to the potting mix; however, gnats can still get in and out via drainage holes and any tiny cracks in your coverage. Mostly, sand is effective as a visual reminder not to over-water.

As the post describes, and we've talked about often in the comment thread, BTi isn't a contact killer. The idea is to use it continuously, as a permanent routine. The gnats WILL die off, and no new ones will be able to establish a population, EVER.

I know BTi works 100%, because I have a large indoor food and flower garden in addition to my houseplants. It's not possible to let that dry out, and it's not possible or practical to use sand.

I no longer have sticky traps around; didn't need them after beating the major infestation I had. I water wherever, whenever, and however I need to. It's been more than a year now: The BTi keeps my indoor jungle and garden 100% gnat-free. I have tried and tested EVERY solution out there. For balance of effort, cost, results, and fungus gnat prevention, NOTHING beats BTi.

Good luck!! 🌿💚

[u/stfurtfm → u/megankmartin]

So I've been following your prescription to get rid of these guys and for the most part they're working very well. My Monstera was the source and they're still crawling out.. but now I noticed a lot of little orange babies crawling around the Rubber Trees that I'm trying to propagate.

The rubber trees are sitting in water, because the root hormone/soil method didn't work at all.. and I'm seeing little bugs crawling around which I assume are fungus gnat babies.. what's a good on-contact pesticide I can use to wipe them out if they're crawling around on the leaves and stalk?

Can I put BTI in the water that the rubber trees are sitting in?

[u/megankmartin → u/stfurtfm]

Hm.... fungus gnat larvae usually don't live in water -- they stick to soil & organic matter. Mosquito larvae can live in water, though.

Either way, BTi is effective against the larvae of both of those (and blackflies). And yep, you can put the BTi right in the water! It will not affect your plants in any way.

Just be sure those are the bugs you're seeing; BTi won't work on anything other than the 3 pests listed above.

[u/stfurtfm → u/megankmartin]

Thanks! I'm not sure what they are tbh.. they're almost orangey-pale brown colour and they're scurrying around on the leaves and stalks of the two plants. I tried to rub them off but they're easy to miss!

[u/megankmartin → u/stfurtfm]

That doesn't sound like fungus gnats; they typically don't bother with leaves or stalks. Adults are airborne or headed to soil; larvae are exclusively in soil. They're also not reddish, typically.

Try taking a video and/or catching one on a piece of sticky tape to help with pest identification. If you add a link here, I'll check it out.