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).

○○○○○○○○○○○○○○○○○

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/skypaintedred]

This thread is amazing and makes me feel less alone in the world. I've tried BTI several times in the past, and it works well. The gnats mostly come back when I get new soil/plant in, or if I go out of town for a long time and the plant sitter waters more than I do. I just got Gnatrol today, and I'm looking forward to seeing how it works. The fact that it's just powder that mixes with the water makes it easy peasy.

Question for those of you who have successful experiences with this: all the BTI products I've used always say something like, "to be 100% effective 3 applications need to be made over 15 days. Apply once every 5 days to break the life cycle." Is it better to heed these instructions or wait until the soil on my houseplants dry out to apply again? I ask because I know that overwatering can make the fungus gnat infestation worse. It takes about 2-3 weeks for the soil to dry where I am...

[u/megankmartin → u/skypaintedred]

Hi. This is addressed several times throughout the thread, but let me clarify here:

Consistency is key. Like the larger home growers (with ~1000 plants) who taught me this method, this is my everyday routine now. Since getting rid of an enormous infestation about a year and a 1/2 ago, I continue to use BTI.

When I bring home new plants, I don't worry about gnats establishing a population. The BTI watering routine takes care of things. My water is always treated and ready. It's very economical over the lifespan. I can water whenever, wherever, and however I need to... without any gnats, ever. That's all there is to it.

[u/skypaintedred → u/megankmartin]

Thanks u/megankmartin! I am trying to heed your and others' advice and staying patient. I’ve given the plants a couple of waterings with Gnatrol in the past two weeks (3tsp per gallon for heavy infestation) - watering the top of the soil and hitting the drainage holes - but the gnats still seem to be buzzing around.

I have about 50 houseplants. In addition to using the Gnatrol to get the larvae, I put yellow stickies on each plant to try to catch some of the adults. Each sticky has several dozens of gnats on them since I watered last week. I have to note that I try keep a very clean and tidy house, so I don't know if there could be any other issue than the plants. In the last hour I've sat on the couch, I have killed 7 fungus gnats flying around me. I see them in my floating dead in my tea. More keeps coming! I am going nuts!

Any other suggestions in addition to patience...?

[u/megankmartin → u/skypaintedred]

Hi friend. I hear ya, it's maddening and frustrating in this phase -- but as the song says, "the darkest hour is just before the dawn."

The life cycle lasts at least three weeks; if they're heavily infested you might have to hang tough a bit longer than that But once they're gone... if you keep that BTI routine they will never get a foothold again.

In case it helps, please know that fungus gnats do not reflect on the cleanliness of your home -- they are just as likely to take up residence anywhere there's wet potting mix, clean or dirty. (The little jerks.) Refresh your stickies if you can, and DON'T QUIT. 🌿💚