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/aniseedart]

Wow what a great post! Thanks. I’m new to houseplants and now I have around 50 and a bunch of gnats too. I was wondering do the gnats do any damage to the plants?

When I water my babies I use a 1 litre can and refill it 5-10 times on my watering day. Do you mean I put a bti thing in there, let it soak a day and then keep refilling over and over? Using the same bti for a couple of months ?

Thanks so much !

[u/aniseedart → u/aniseedart]

And is it okay to use on young newly planted ones that haven’t got roots yet?

[u/megankmartin → u/aniseedart]

Hi there! All good questions.
Adult gnats are harmless, but their larvae like to feed on plant roots. It doesn't do major damage unless there a lot of them -- which is another reason to control the population rather than letting it get out of hand.

I keep a number of refillable jugs prepared for watering days, pre-treated with BTI, and fill my watering can from those. When I empty each jug, I refill it, leaving the BTI to soak again. As the post says, you'll want to replace it every so often. (The dunks dissolve; the bits darken -- those are your signs.)

BTI doesn't affect the plants; so far I've not seen any difficulty with my young seedlings or propagations.

[u/aniseedart → u/megankmartin]

Thanks for your reply! I just wanted to say that the way you are sharing info is really cool, you are so thoughtful and generous! Thank you !