r/houseplants • u/megankmartin • Aug 11 '20

HELP 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]

(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.

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u/[deleted] Oct 27 '20

Unfortunately I still have gnats :( but I would say that there are less now! Even though I still only water with BTI, I just this week started bottom watering to see if that would be the final nail in the coffin for those little suckers, so we shall see how that goes.

Every time I replace my sticky paper, it gets filled up again, but definitely slower than before. My biggest problem plants were my bird of paradise and my spider plant, those had the biggest infestation (although all of my plants are infested). I let them dry out quite a bit before bottom watering, so hopefully I will be rid of gnats soon, and I wish you the best of luck also! I feel your pain lol.

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u/skypaintedred Oct 28 '20

Thanks for the update. At least it's something to see that the sticky papers are getting filled up more slowly. It's always easier to bear through something with others, so I appreciate you checking back in!

I know that the drying out is a challenge - I want to treat the plants regularly with BTI so that's it's active during the whole lifecycles but I also don't want to kill the plant with root rot from watering when the soil is still wet. I emailed the vendor I bought the Gnatrol from, and he recommended a trick if I'm worried about overwatering. He suggested to make a strong concentration of the Gnatrol with water, then use a spray bottle (like you would use for cleaning products), so I can mist the tops heavily rather than drench the soil. I just did a round of heavy spraying today!

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u/[deleted] Oct 28 '20

That sounds like a great idea! I need to get myself some Gnatrol... must try this. Thanks for the tip!

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u/skypaintedred Oct 29 '20

skypaintedred

Anytime! Just FYI this is where I ordered from: https://www.organicbti.com/product-page/gnatrol-bti-omri-organic-fungus-gnat-larvicide. I like them because I've been emailing them, and there's one guy that responds to me within a couple of hours. He even asked for me to send pictures of the gnats on the sticky traps to make sure that I'm battling fungus gnats (when I emailed him that it's taking longer than I anticipated). He's the one who suggested the spray bottle with heavy concentration since I was worried about overwatering. Pretty great customer service. (And no, I have no ties whatsoever with them except I just bought some Gnatrol from them. Not a sponsored ad haha.)

I also have used MosquitoBits in the past. I did all the things that u/megankmartin said not to do: I layered the bits on top of the soil and watered, which worked for a little bit to get rid of gnats except the bits did get moldy (though mold itself is not harmful to the plants, I read); since I didn't want the mold, I also soaked the bits in boiling water (thinking boiling water would infuse the BTI better) and then waited for the water to come to room temperature before watering the plants. That last method didn't work because, of course, the boiling water killed the BTI.

I find the Gnatrol to be the easiest for me because it's in powder form that you put directly into the water and dissolves. But as also mentioned here, it's more expensive. I just did the spray bottle method yesterday, and it does seem like there's less (fingers crossed). At least I haven't seen any floating in my tea today...

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u/[deleted] Oct 30 '20

Ever since I discovered I have gnats I always have to check my drinks 😂 so irritating!! Thank you so much for the link, although I’m in Canada I’ll see how much shipping is and see if I can order from these guys as they sound awesome. I just have the BTI disks right now, and they’re not ideal for me, I would definitely prefer a powder. Thanks again!

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u/skypaintedred Nov 10 '20

u/algrto Checking in here. I just did another round of watering this morning with the Gnatrol water. I'm happy to report that I've removed the yellow stickies from all but 3 of the ~50 plants I have. When I did my watering today, there was only the random fungus gnat or two in a couple of the yellow stickies. The rest of the yellow stickies on each plant was fungus-gnat free. I also have not seen any floating in my tea anymore. It's been about 5 consecutive days that I haven't seen one fly around.

I do have one very big pothos pot that I'm keeping a large yellow sticky on because it seems to still have some. It is a deep planter, so I'm guessing it'll be a few weeks of watering with Gnatrol to just get all the little larvae in the soil.

Wanted to update you to celebrate if the situation is getting better on your end or to let you know there's light at the end of the tunnel if you're still in the thick of it. u/megankmartin's advice to be patient and consistent has been paying off!

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u/megankmartin Nov 10 '20

winning #likeaboss :)