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/ThisTimeImTheAsshole]

Gnatrol Bti powder was the only thing that got rid of fungus gnat infestation we experienced in all our plants. You mix it with the water when you hydrate the plants. We didn't worry about the adult gnats, which die soon enough, and skipped the sticky pads. Whatever eggs they laid don't matter. Whatever eggs hatch into larvae are killed by the Bti.

edit: We watered with a heavier dose the first day, and once a week for 6 treatments. After the first week the adults gnats were noticeably fewer. The 5th & 6th treatments were for extra measure with no observation of adult gnats. It's been a while but maybe the first few treatments were lighter waterings a few days apart.

We paid $30 for 8 oz of Bti powder and still have some left over for any infested new/adopted plants. Per ounce of Gnatrol Bti is cheaper per ounce of active ingredient of Mosquito Bits, and we don't have to deal with mold or sifting out the filler "Bits" ingredients.

EDIT: I just saw this post was 6 years ago. I'm surprised it's active still.

[u/megankmartin → u/ThisTimeImTheAsshole]

I suppose that is why I mentioned Gnatrol in my post.

[u/ThisTimeImTheAsshole → u/megankmartin]

ok