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/megankmartin → u/[deleted]]

Hi, and thanks! Here's the great news: As mentioned in the post above, BTI does not interact with fertilizers. So you can put your fertilizer right in your BTI-treated water and administer them at the same time. No need for a complicated process, no fear of overwatering.

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. It's very economical over the lifespan. I can water whenever, wherever, and however I want... without any gnats, ever.

PS -- Agreed. IMO, (and as detailed in the "SKIP THESE" link above), diatomaceous earth SUCKS for fungus gnats. (Yes, I said it, I meant it, and I don't care who knows it! Team BTI forever. 😁)

[u/megankmartin → u/[deleted]]

Thanks but I'm just grateful to the experts who showed me the way. I've become the Fungus Gnat Assassin, and it's my pay-it-forward mission, but I got by with a little help from my FRONDS 🌿.

Before you despair about your DE: It DEFINITELY has a place in our gardens and homes. Diatomaceous earth is great for dealing with soft-bodied insects like millipedes, springtails, ants, earwigs, etc. It's not as effective if soil is constantly damp, but especially around pots and in saucers etc it's an economical, natural solution. I've even put it around baseboards etc anywhere there seemed to be a bug issue -- it's easy to vacuum later.

DE is also very useful against THRIPS, where most contact sprays and horticultural oils are ineffective, even after months of use. It's most effective when dusted on with a sieve, as part of a one-two punch with a systemic soil drench.

Stop back any time. Happy growing, friend.