If tiny black flies are hovering over your houseplants every time you water, you are probably fighting fungus gnats — and the part you can see is only half the problem. The adults are annoying, but the real damage is happening underground, where their larvae chew on fine roots in the top few inches of soil.
That is exactly what Mosquito Bits are for. They carry a naturally occurring soil bacterium called Bti that kills fungus gnat larvae when they eat it — and nothing else. No harsh chemicals, no repotting everything, no throwing plants away. This guide shows you how to mix the tea, how often to use it, and the mistakes that make people think it “didn’t work.”
Quick answer: Soak 1 tablespoon of Mosquito Bits in 1 gallon of water for 30 minutes, strain out the granules, and water your plants with the tea until it drains. Repeat every 5–7 days for 3–4 weeks, and hang yellow sticky traps for the flying adults. Larvae die within 24–48 hours of eating the Bti; the adults fade over the next 2–3 weeks as no new gnats hatch.
What Are Mosquito Bits, Exactly?
Mosquito Bits are small corn-cob granules coated with Bacillus thuringiensis israelensis — Bti for short. Bti is a naturally occurring soil bacterium that produces proteins toxic to the larvae of certain flies, including mosquitoes, blackflies, and fungus gnats. It has been used for mosquito control for decades and is registered with the EPA.
When fungus gnat larvae feed in treated soil, they ingest the Bti proteins, which disrupt their gut so they stop feeding and die, usually within 24–48 hours. The key word is ingest: Bti only works on larvae that eat it. It does nothing to eggs, pupae, or flying adults — which is why one treatment never finishes the job, and why the repeat schedule below matters more than the dose.
Just as important is what Bti does not do. It does not harm your plants, your pets, or you when used as directed on the label. It does not kill earthworms or beneficial insects. That is what makes it a good fit for houseplants: you can treat the soil your plants live in without treating the plants themselves.
First, Make Sure They Are Fungus Gnats
Mosquito Bits only help if the flies are actually fungus gnats. If the flies are hanging around ripening fruit or the trash, they are probably fruit flies. If they are fuzzy little moth-like flies near a drain, they are probably drain flies. Fungus gnats hover around the soil and pots, run across the soil surface, and show up near windows and lights.
Still unsure? Hold a piece of white paper just above the soil and tap the pot. Fungus gnats will jump and fly up from the soil; fruit flies will mostly ignore you. If you want the full identification walkthrough, our fungus gnat guide covers the look-alikes in detail.
The Mosquito Bits Tea Recipe
You have two ways to use Mosquito Bits: sprinkle them dry on the soil, or soak them in water first and use the water. The tea method wins for houseplants. Soaking releases the Bti into the water, and watering with it carries the Bti down into the top few inches of soil where the larvae actually feed. Dry granules sprinkled on damp soil often go fuzzy with mold before they do much good.
Follow your product label first — dosing varies by brand. The standard tea recipe most growers use is:
| Pot size | Mosquito Bits | Water | Steep time |
|---|---|---|---|
| Small pots (4–6 inches) | 1 teaspoon | 1 quart | 30 minutes |
| Medium pots (8–10 inches) | 1 tablespoon | 1 gallon | 30 minutes |
| Large pots (12 inches and up) | 2 tablespoons | 2 gallons | 30 minutes |
Use room-temperature water, and make a fresh batch each time you treat. Mixed tea is not something to store for weeks — mix what you need, use it, and start fresh next time.
How to Apply the Tea in 6 Steps
- Measure the Bits. Use the table above for your pot size. A kitchen measuring spoon is fine — no precision lab work needed.
- Soak for 30 minutes. Stir the Bits into room-temperature water and let them sit for at least 30 minutes. Give it a stir halfway through.
- Strain out the granules. Pour the tea through a fine strainer or cheesecloth into your watering can. The granules have done their job; leaving them on the soil just invites mold.
- Water thoroughly. Pour the tea slowly and evenly across the whole soil surface until water runs out of the drainage holes. The Bti needs to reach the top few inches of mix, where the larvae live — a light sprinkle on one side will not do it.
- Empty the saucer. Dump any runoff after 10–15 minutes. Standing water keeps the soil wet, and wet soil is what invited the gnats in the first place.
- Treat every plant with gnats — and the ones next to them. Adults fly between pots, so treat the whole shelf or windowsill, not just the worst offender.
How Often to Repeat (and Why 3–4 Weeks)
This is the part most people get wrong. Bti kills larvae, not eggs, pupae, or adults. Eggs already in the soil will hatch after your first treatment, and pupae will keep emerging as adults for days. One drench kills one generation of larvae; the schedule kills the infestation.
Use Bti-treated water every time you water — or at least every 5–7 days — for 3–4 weeks. That covers the full fungus gnat life cycle, which takes about a month indoors at typical room temperatures, with adults living about 7–10 days, according to the University of California IPM houseplant guide.
| Week | What is happening | What to do |
|---|---|---|
| Week 1 | Larvae die within 24–48 hours of eating Bti; adults still flying | First tea drench; sticky traps up |
| Week 2 | Fewer new adults emerging; traps start catching less | Second and third drenches, every 5–7 days |
| Week 3 | Trap counts drop sharply if the schedule held | Keep treating; let the top 1–2 inches of soil dry between waterings |
| Week 4 | Only the occasional stray gnat | Final drench; if traps are nearly empty, you can stop |
If your home is warm or the infestation was heavy, keep going for 6–8 weeks. Consistency matters more than intensity — a steady weekly drench beats one heroic soak followed by nothing.
Mosquito Bits vs. Dunks vs. Gnatrol
All three products use the same active ingredient, Bti. The difference is format and convenience.
| Product | What it is | Best for | How to use |
|---|---|---|---|
| Mosquito Bits | Granules | Most houseplant collections | Tea method above; easy to dose per gallon |
| Mosquito Dunks | Solid rings | Watering cans you refill often | Steep 1/4 dunk per gallon for 30 minutes; reuse the dunk |
| Gnatrol | Liquid concentrate | Large collections or greenhouses | Mix per label; no soaking or straining |
For a typical home collection, Bits are the easiest starting point. Dunks are handy if you water from the same can every time — just drop a piece in and leave it. Gnatrol is overkill for a few pots, but it is the tidiest option if you have dozens of plants.
Pair It With Yellow Sticky Traps
Mosquito Bits handle the larvae. Yellow sticky traps handle the adults — and they are how you know the plan is working. Adults that keep flying around keep laying eggs, so catching them shortens the infestation and gives you a visible scoreboard.
Stick traps right at the soil line, not across the room — adults hang out where they hatched. Use 1–2 traps per medium pot and replace them when they are covered, usually every 7–14 days. If the number of gnats on fresh traps drops week to week, you are winning. If it does not drop after 2–3 weeks, something else is off — usually the soil is still staying wet on top, the Bti is not being applied with every watering, or there is another breeding spot nearby, like an open bag of potting soil or a drip tray full of water.
5 Mistakes That Waste Your Mosquito Bits
- Treating once and stopping. One drench kills the larvae alive today. Eggs and pupae survive it. Without repeats, the next generation replaces them.
- Treating one plant and ignoring its neighbors. Adults fly. If you only treat the worst pot, the gnats next door will re-infest it.
- Sprinkling dry Bits and leaving them. On damp soil the granules go fuzzy with mold and release little Bti where the larvae feed. Make the tea and strain it.
- Watering the tea onto dry, hydrophobic soil. If the mix has dried out and shrunk from the pot edges, the tea runs down the sides and out the bottom without wetting the root zone. Bottom-water for 15–20 minutes first, or water slowly in two passes.
- Using an old, open bag. Bti products lose potency with age and poor storage. Check the date on the bag, keep it sealed and dry, and replace it if it has been open for years.
When Mosquito Bits Won’t Fix It
Mosquito Bits are a larva-killer, not a cure-all. If the flies are not fungus gnats, Bti will do nothing — confirm the ID first (see above). If the soil smells sour and stays soggy for a week or more, the mix itself is the problem: no treatment fixes a pot with no drainage or a mix that never dries. In that case, repot into fresh, chunky mix and check the drainage holes — and read our guide to saving an overwatered plant before the roots give up entirely.
Seedlings and cuttings with heavy larval feeding may still struggle even after the gnats are gone, because the larvae have already chewed the fine roots. Give them time, keep the soil barely moist, and expect slow recovery — or start a fresh cutting if the plant is failing. And if you have already treated for 6–8 weeks with no drop in trap counts, look for a hidden breeding spot: an open bag of potting mix, a self-watering reservoir, a humidity tray, or a cachepot holding water under the nursery pot.
After the Gnats Are Gone: Keep Them From Coming Back
Once the traps are nearly empty, the work shifts to prevention. Let the top 1–2 inches of soil dry between waterings — that alone makes your pots far less inviting. Empty saucers and cachepots every time you water. Seal open bags of potting mix, and quarantine new plants for 2–4 weeks before they join the collection — fungus gnats often arrive in newly bought plants. Our overwatered vs. underwatered guide can help you find the watering rhythm that keeps the surface dry without stressing the plant.
Frequently Asked Questions
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Do Mosquito Bits kill adult fungus gnats?
No. Mosquito Bits only kill larvae. The Bti has to be eaten by larvae feeding in the soil, so flying adults are untouched. That is why you pair the tea with yellow sticky traps: the Bits stop new gnats from hatching, and the traps catch the adults already flying. Expect the adults to fade over 2–3 weeks as no new ones emerge.
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How long does it take for Mosquito Bits to work on fungus gnats?
Larvae die within 24–48 hours of eating Bti in treated soil. You will not see that directly, though — what you see is fewer adults on your sticky traps over the next 2–3 weeks. If trap counts are not dropping after 3 weeks, check that you are treating with every watering and that the soil surface is drying between waterings.
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Can I just sprinkle Mosquito Bits on the soil instead of making tea?
You can, and the label allows it, but the tea method works better for houseplants. Soaking releases the Bti into the water, and watering carries it down to where the larvae feed. Dry granules left on damp soil often go fuzzy with mold and release little Bti. If you do sprinkle, water them in right away and remove any moldy granules.
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Are Mosquito Bits safe for pets, kids, and my plants?
Yes, when used as directed on the label. Bti targets the larvae of certain flies and does not harm plants, pets, or people. Still, store the bag out of reach of children and pets, and follow the label instructions — it is a pesticide product, even a gentle one.
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How often should I water with Mosquito Bits?
Use Bti-treated water every time you water, or at least every 5–7 days, for 3–4 weeks. That covers the full fungus gnat life cycle. For a heavy infestation or a warm home, keep going for 6–8 weeks. Once the traps are nearly empty, you can stop and switch to prevention: letting the top 1–2 inches of soil dry between waterings.
Related Rescues
- How to Get Rid of Fungus Gnats in Houseplants — the full plan this article fits into, from ID to prevention.
- How to Use Neem Oil on Houseplants (Without Burning the Leaves) — neem helps with other pests, but it is a weak fungus gnat tool on its own.
- Sticky Leaves on Houseplants: 3 Causes and How to Fix Them — if the sticky stuff on your leaves is honeydew, the culprit is a sap-sucking pest, not gnats.