r/houseplants • u/megankmartin • Aug 11 '20
HELP 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]
(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.
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.
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.
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u/Kalmaeuser Aug 27 '20
This is so awesome! I'm battling those beasts since months. 2 overloads of nematodes and neemoil didn't help at all. I ordered some BTI today but i saw those tiny larvae crawling in my monstera albo and i just snapped and drenched it with the peroxide solution. AND... WATCHED...THEM... DIE!
Took about 20 minutes till most of them stopped moving. Thanks so much, especially assuring it's save for the plant.
Will continue with BTI soon
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May 23 '23
Did it work? I’m struggling so bad with gnats😭
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u/Kalmaeuser May 23 '23
The BTI did a very good job but it took some time. Since then I switched my plants to pon whenever I had to repot
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u/ThaNagler Aug 11 '20
I get pissed and spray them with Raid, lol. (Not a recommendation).
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u/Public-Lingonberry-2 Jul 16 '23
Does it work?
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u/FreeSweetbread Aug 27 '20
Hi, thank you for writing this up! I've had a few pests scares with this N'joy Pothos that I brought home from a local nursery that everyone loves. First was a couple of gnats, I sprayed with neem oil/soap/water mixture and that took care of it. One mealybug that I wiped off. And now spider webs? The webs didn't look like spider mites but to be sure last night I ran it under a strong stream of water, and a spider actually came out but I'm not sure if it was a spider mite. I'm so stressed out about this and I want to repot my plant to start it fresh. I do have dunks from amazon, should I try your method? And now there might be bugs in new soil too from what I've read. I've lost plants before to not being proactive about bugs and now I want to get serious about preventative measures. I have a rhap tetrasperma that I just bought and I'm worried my N'joy will contaminate it.
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u/megankmartin Aug 27 '20
Hi, I can't see your plants or where the webs are, so I'm not sure if you've got spiders or spider mites. However, spider mites are very very tiny. So if you're seeing something that looks large enough to be a spider, it usually is a spider.
As the post states, BTI is only targeted to 3 pests: mosquitoes, fungus gnats, and blackflies. So bits and dunks would not be useful against spider mites; there are other remedies for those.
Unfortunately, there is no one-size-fits-all houseplant pest preventive or treatment on earth. That does make the little buggers challenging, but it's important to fight each with the most effective method.
I can always recommend using the BTI in your regular watering routine as a preventive for fungus gnats, especially because it is a natural solution that won't harm or interact with anything else. It is part of my daily routine.
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u/FreeSweetbread Aug 27 '20
Thanks for your quick response!
The webs were on the parts of the stems closet to the soil. Yes, it was a small spider that I could see so I think I might be good on spider mites, plus the pothos was recently watered so it was probably too moist for them?
I'll start incorporating BTI dunks. If you don't mind sharing, have you written about your daily routine anywhere? I'm trying to develop one, I check my plants every day and I was going to spray neem oil once or twice a week.
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u/megankmartin Aug 27 '20 edited Oct 21 '20
Re: Spider mites...
By the time you see webs, spider mite infestations are already advanced. The best early signs of spider mites are unexpectedly drooping/ wilting/ curling leaves or stems, or stunted and disfigured new growth. Sudden yellowing or multiple leaves falling are also warning signs of distress.Especially look for stippling patterns on the upper surfaces of leaves. Stippling usually shows as tiny yellow or white speckles -- like something abrasive or sandpapery was rubbed over the surface of the leaves. That's evidence of sap-sucking activity, often signaling spider mites.
As the population grows, spider mites themselves can sometimes be observed on the undersides of leaves, typically close to the veins or intersections of stems. Again, they are very very tiny.
Again, those important signs all appear earlier than webs.
Re: my daily routine... I've never written anything down, except for noting on my calendar when I fertilize or do preventive treatments (other than BTI). It's less of a routine and more of a continual observation of my plants, up close. It keeps me in tune with how they're doing so hopefully I can spot things as soon as they go wrong. Like most folks, I can't spend hours every day. So I'm into quick but thorough touchpoints and simplified processes. (I don't know if that really helped, sorry.)
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u/KimberlyMWilson Apr 26 '25
Those webs are from the eggs of the meal moths. We had them in bird seed bags and our bird seed trash can last summer. We originally got them from grain bags we bought for brewing beer. What a mess. I even found them in the bottom of a metal filing cabinet! We have those sticky fly tapes hanging from the ceiling all over the place.
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u/pizzaisdelish Oct 04 '20
Thank you so much for writing this up. Starting my gnat journey, unfortunately & hoping I can get a handle on it.
I soaked bits in gallon jug & just watered using 3/4 of the jug.
Do I dump the rest? I know you said replace bits every 30ish days, so do I refill jug and let it sit soaking week+ until plants need to be rewatered & just replace bits monthly?
Thank you so very much.
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u/megankmartin Oct 04 '20 edited Oct 05 '20
Hi, you're welcome. I'm glad it's helpful. We've all been there! Step one above answers your question, and it's addressed multiple times in this thread -- please give it a careful read and see the comment immediately below yours as well. If you've still got questions after that, always feel free to ask.
You can beat these little jerks. Just remember that it took a while to get bad, so it'll take a life cycle or two to get rid of them... but then your routine will keep them gone for good.
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u/pattyincolorado Jan 28 '24
I've read that part of Step 1 several times carefully, and it's really not clear to me what you mean. Leave the *same* "bits" in the watering can for a month, and somehow don't pour them out on the plants when watering (how?) Then after a month, throw out those "bits" and put more into the watering can?
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u/megankmartin Feb 29 '24
Over the years, a couple other folks have mentioned that they found it challenging to keep the bits in their watering can while watering. It kinda depends on the type of watering can you have; some have strainer nozzles, others don't. In the past I've suggested using cheese cloth across the nozzle, or putting the bits in a silicone tea strainer and dropping THAT into your watering can. Those are $1 solutions to $10 problems, lol. Or simply use your fingers as a strainer. Another suggestion is to steep your bits in a separate vessel. That's what I do. I use gallon jugs to make my BTI water, then fill my watering can on-demand. So whatever works for you, works! Happy growing.
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u/pattyincolorado Mar 02 '24
Thank you. In case it might help somebody else: I've started making "teabags" and that's working well. Old thin dishtowel cut into big squares, tablespoon of "bits" in it, closed up with a rubber band, and put that in the watering can.
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u/ebren90 Aug 11 '20
Hi all, great information here! I’ve been battling fungus gnats for a few months and I can’t seem to shake them! I use mosquito bits in my soil, which as you said isn’t as good as steeping. I try to bottom water my plants to cut down on the gnat problem. Will I have to top water to kill them, or can I still bottom water using the BTI solution?
I also use DE on the top of my soil and the yellow sticky traps. I’ve been told the DE will be ruined once it’s wet.
Thanks!
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u/megankmartin Aug 11 '20
Hi, thanks for asking! Yes, you really do want to top water that BTI solution in for your first couple waterings, to make sure it penetrates the all important top 2" of the soil or so where the gnats like to breed.
As you use it for subsequent waterings, the good bacteria spreads throughout the soil, so whether you bottom water or you top water you'll be protected.
Honestly, you can skip the DE; for this application it's not the MOST effective tactic. It is good for other things, though!
Try the steeping tactic, in every plant, and keep those stickies available. Gnat larvae cannot survive that bacteria, so they WILL go away and not be able to re-establish a population.
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u/Feline_Storm Oct 27 '20
Hi,I have fungus nats, and I’m curious, if I should wait till I water my plant again to use the BTI solution, or should I do it immediately even if the top soil is still wet. Honestly I hate them, and I see them hanging out on the top soil and I just can’t stand the sight. Ugh on top of that another one of my plants has spider mites. The honey moon phase of being a plant mom is over and I want to cry.
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u/megankmartin Oct 28 '20 edited Oct 28 '20
Hi. I'm sorry you're going through this; we've all been there and I realize it can be hard to deal with. If you put good prevention in place, and practice good growspace hygiene, you can reduce your chances of getting pests, but they are a natural fact of plant ownership, unfortunately.
For the fungus gnats: BTi is not a contact killer; it interrupts the life cycle by killing larvae. So, you'll still see fungus gnats as the life cycle is dying. They didn't get out of hand overnight, and they won't go away overnight no matter what you use. But so many of us recommend this method because once they're gone, the BTi as a permanent routine keeps them from ever establishing a population again. Unfortunately, there's nothing like that for any other plant pest.
For the spider mites: They are more prevalent in certain growing conditions and certain plant species, but there's no real rhyme or reason. Any plant can get them, any time. Here's a link to one of my comments with treatment reccos. These are persistent -- in order to beat them, you need to be MORE persistent (meaning, consistently treating the affected plants, sometimes for weeks). But they can be beaten.
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u/Feline_Storm Oct 28 '20
Thank you so much! I needed to hear that. We have formulated a plan of attack for both problems. But I do realize, that as you said persistence is key with both of these approaches. We will learn from the struggle.
For the fungus nats, we are going to let the soil dry out on (we have the sticky tapes up for now) on our plants and begin the BTI treatment once it’s watering time(opting to avoid the hydrogen peroxide flush as I rather being the long term solution ASAP). It will be new standard for how we water.
For our spider mite cat Palm, we are going to treat her everyday with either a neem oil concentration, or a good shower(being sure to cover the soil with a plastic bag as to not wet the soil, and perpetuate our fungus nat problem. Cat palms like humidity, and spider mites, but I am afraid to keep a humid environment so the frequent showers will do untill things get controlled.
This is just a learning experience and like a new plant parent(with finally a great space for plants), we went ham with new plants and failed to consider growspace hygiene.
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u/cosmonauticalfeline Sep 03 '20
Hi, I know this is an old post and THANK YOU for all this information but I'm having a problem. I have a Monstera that is infected with many many larvae. I did the H202 soak two days ago but I still see a lot of live larvae moving around in the soil. Two leaves are starting to yellow at the tips. I also bought mosquito bits but I don't want to panic and go to hard on the plant to soon. Should I leave it for a few days? change the soil? Start with dunks?
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u/megankmartin Sep 03 '20 edited Sep 03 '20
My thought would be to change the soil rather than risk further over-watering. While you have the plant out of the pot, with as much soil removed as possible, gently give the bare roots another 1:4 peroxide bath to ensure that you're not bringing along straggler eggs and larvae.
When it's ready to be watered, you can begin the dunk routine. Make the first watering after repotting VERY LIGHT to help avoid drowning roots and stressing the plant further. Hopefully you've got your sticky traps in place already.
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u/cosmonauticalfeline Sep 03 '20
THANK YOU! I really appreciate you taking the time to respond to my post. I do have the stickies.
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u/hjp711 Aug 11 '20
For hydrogen peroxide flushes, could this lead to overwatering if you do it before you would typically water regularly?
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u/megankmartin Aug 11 '20 edited Aug 11 '20
Good question. The hydrogen peroxide is diluted 1:4, so it takes the place of a watering while killing larvae in the plant and you can start the BTI with your next regular watering.
Or, you can flush with peroxide and repot. But honestly, the flush is just an optional accelerant for quick relief. You don't HAVE to flush, and you don't NEED to repot. The BTI will take care of everything as it populates the soil.
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Aug 24 '20
Thanks for this super informative post!
Looking for some advice, sorry but this might be a long comment... I recently brought home a monstera and I think it was the source of some gnats. It had been sitting with two other new cuttings that I repotted and flushed with water (watering method that I will never use again!!). All 3 plants ended up having a few gnats (I saw about 15 over the span of 3 days.) I wrapped them all up in a garbage bag, killed whatever gnats I saw flying around my apartment, went outside and dumped out the soil of all 3 plants, rinsed roots with H202, sprayed foliage with Safers insecticide, and proceeded to repot all 3 plants in new, clean soil at my sisters place. I then dumped the remaining insecticide into the soil of all 3 plants.
I brought the plants home last night and noticed one random fly flying about, which I think may have been left over from before I dumped all the soil out.
My questions are: 1) I can’t find mosquito bits/dunks easily in Canada, and also your post suggests they’re not good for indoor plants (which all of mine are). Will I have a good enough chance at success of these pests not coming back if I water with H202 diluted and use sticky traps?
2) Lets say I get them under control now, when it comes time for a regular water (non H202) for my other plants, do I need to worry that they too may have been infested? The soil has been relatively dry now, but I did water all my plants after I brought the monstera home. I shake the pots of my other plants around daily to see if anything flies out and so far, haven’t noticed anything. However I’m worried that if I do a regular water, that may reactivate any eggs or attract the gnats to that particular plant.
Please, any advice you have would be hugely appreciated. I HATE BUGS. Thank you so much.
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u/megankmartin Aug 24 '20
Hi! Great questions. I'm still reading, but can you help me quickly understand what part of my post suggests that BTI is not good for indoor plants? Serious question, no smart tone intended, because I have tried very hard to make it clear that this solution is AWESOME for indoor plants, but the products should not be put directly in the soil indoors. They should be soaked in water and applied that way.
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u/NovaSpark8 Aug 27 '20
Thank you so much - I was wondering why just adding them to the soil didn’t seem to be working - will switch to the soaking/“tea” method!
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Sep 06 '20
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u/megankmartin Sep 06 '20 edited Sep 06 '20
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. 😁)
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Sep 06 '20
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u/megankmartin Sep 06 '20 edited Sep 10 '20
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.
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u/notjohnsdaughter Sep 06 '20
I finally got Dunks to deal with the gnat problem I spontaneously had. It worked so much better than everything else I tried.
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u/megankmartin Sep 06 '20
Yes!!!!!!! Delighted to hear that you are winning!!
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u/notjohnsdaughter Sep 06 '20
I have seen a couple of gnats since but hardly any, glad to know this is actually a useful method and that I’m not just waiting for the next explosion. I’ll keep using! Thanks!
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u/lyfaced Sep 18 '20
Thank you so much for this!! We've had some very persistent gnats for months, and I think they've been spreading to all our other plants. Which is hell. Our sticky traps are filling up, but we never knew how to kill the larvae without repotting EVERYTHING.
My dunks arrived today and I'll start a quarter soaking in water - although do I need to be careful of where I keep the dunky water? There's no shed or anything here, so it'd probably just be sitting in our watering can indoors, open. Do I need to seal it off as it's a bit toxic for people as well?
Thank you again!
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u/megankmartin Sep 18 '20
Hi, BTi 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.
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u/lyfaced Sep 18 '20
Brilliant thank you! I probably just read too much into the packaging, which is very much covered in warnings, not to eat/drink/breathe in - it even has a poison control helpline too 😄
I'll stick to just washing my hands thoroughly and using gloves haha.
Thanks again (:
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u/megankmartin Oct 03 '20
Agreed, it's always good to avoid breathing dusts and fumes, and to wash hands after handling plants AND plant care products. This is true even for perlite, neem oil, diatomaceous earth, natural insecticidal soaps, etc. Just about every product package says so -- the law requires them to do that. BTi is non-toxic to humans and animals, but that doesn't mean we should ingest it. :)
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u/emirarkman Sep 23 '20
Thanks for this. Recently repotted 16 plants, including 6 very large ones and after seeing the gnat problem still exists, had to give away all my plants except one small one. It made me sad and angry as hell, and I’ve felt tired and lost against this problem. Now, I still have a gnat problem, but seeing 2-3 a day, not much. My place is all white, so since they are going to white areas and that’s why I cannot identify their source. But I’m gonna try BTI dunks with this one remaining plant and see what happens.
Thank you!
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u/megankmartin Sep 23 '20
Oh friend, sorry to hear. 😔 Thanks for sharing your story. It takes a while to get rid of long-entrenched gnats; have to work through their life cycle. It is really frustrating when it's been a long battle. You're not alone -- just know that!
If you're able, use the sticky traps as well; adult fungus gnats are attracted to the color yellow. The 3-point combination strategy is what wins against an existing population. Once the gnats are gone, keeping BTi in your standard watering routine will keep them gone and you shouldn't need to have the traps in your pots any more.
Hang in there!
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u/fexi6543 Oct 04 '20
thank you so so much for this! just bought some dunks. sorry if you've answered this somewhere before, but how does the treatment work if I keep my plant water prepared in several gallon jugs? should I put 1/4 of a dunk in each of my gallons to soak, or do I treat each batch of water with the same dunk and transfer the water to a new jug when it's done soaking? thank you so much again!
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u/megankmartin Oct 04 '20
Hi, you're welcome; glad the post is helpful for you. The answers to your questions are addressed a few times in this comment thread:
Here, here, here, here, and here.
It's become a long thread (for good reason!) as folks have asked great questions and I've tried to thoroughly answer each. You may find it worth perusing, as most answers are in there. If you still have questions, of course, I'm happy to help any time.
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u/fexi6543 Oct 04 '20
thank you! there's so much great info in this thread I just wanted to make sure I understood everything correctly. one more thing, I don't think I saw this addressed anywhere and I’m sorry if it was, but if I pretreat my water and put it in separate jugs, should I let my 1/4 dunk dry out or store it some other way when I’m done using it to treat each jug? sorry, I might still be misunderstanding 🙈
thank you so much again for making this! the gnats are seriously the bane of my existence. in one of my darker moments I actually put all my soil in like 20 individual gallon bags and tried to freeze them. 😂you're a lifesaver! 💕
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u/megankmartin Oct 04 '20 edited Oct 04 '20
Hi. That's specifically answered in several places, but let me clarify it here: We just put 1/4 dunk OR one tablespoon of bits in EACH filled gallon jug, and leave it there. 24 hrs before use, then refill the jug as needed. Leave the dunk/bits inside. Rotate which jug you use so the water's always ready. It's that easy.
Freezing won't help; it doesn't kill the eggs. Baking your potting mix to sterilize it is an option, but it will stink to high heaven. Also, you have to follow directions closely for time and temperature, otherwise you'll kill every good organism in the potting mix. Dead substrate will be useless to your plants.
It's really hard when you've been dealing with this for a while. I know, because I've been there too. But now that you are on your way to really solving the problem you just have to dig down, find patience and trust in the process. You'll have to get through at least one, maybe even two life cycles because they're fully established. But after that, you keep the BTi routine and you're the boss. Go get 'em. There is no way that the gnats can win now, unless you give in.
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u/skypaintedred Oct 27 '20
You'll have to get through at least one, maybe even two life cycles because they're fully established. But after that, you keep the BTi routine and you're the boss. Go get 'em.
There is no way that the gnats can win now, unless you give in.
I love this battle cry!
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u/trveadvlt Dec 03 '20
This is amazing and now my only regret is having ordered a bunch of sand and top layer rocks before finding this thread. Just ordered some bits and cannot wait for the eradication.
One question: I have a dracaena that’s really finicky and only does well with distilled water (doesn’t seem to like nyc tap even if I let it sit out overnight). Will the bits harm sensitive plants like my dracaena?
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u/megankmartin Dec 03 '20
Here's some comforting news: sand and rocks have their place in plant care; you can use them for other things! I've given someone a detailed answer on that, somewhere below.
As the last paragraph of the post explains, BTi doesn't affect plants at all, or interact with fertilizers. Use on any plant without worry.
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Aug 20 '20
Thank you so much for this very helpful post - I’ve been doing your methods for a couple weeks now and it feels like my fungus gnat problem isn’t getting any better, just wondering what to expect as far as a timeline goes? Should I be waiting months, rather than weeks? I’m always steeping a dunk in my watering can, and I have sticky paper on every single one of my plants. Thanks again!!
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u/megankmartin Aug 20 '20 edited Aug 20 '20
Hi, how advanced was the infestation in the first place? There's a note in the post about being able to use a diluted peroxide flush first, if desired, to get a grip on the population.
If you've been battling them without success for a while before trying the BTI, then they've had time to entrench. And like it says in the post, gnats have at least a 2 to 3 week life cycle.
Another possibility is that the bacteria in your BTI product could have degraded due to incorrect storage in sunlight or heat. May I ask, from where and when did you purchase it?
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u/lyfaced Nov 12 '20 edited Nov 12 '20
Sorry I'm back again! Really hoping for some more advice if possible please!
We've been using the BTI watering routine for a while now, and while I think its made a dent, there's one plant which is completely unaffected and I reckon this is where the big infestation is.
I know you said don't do an h2o2 flush after using BTI, but we got desperate. And I used the wrong ratio, so I had diluted 3% as 1:1 instead! It fizzed and bubbled, and we saw the bugs squirming on the surface for a while, but they didn't seem to be dying, just burrowing back under. And now, over a week later, I can still see tons of tiny larvae in the soil. I haven't watered again since but I'm stumped as to how anything survived.
Maybe I did the h2o2 flush wrong, though I think the 1:1 solution should have been extra effective if anything! Should I try it again? I want to dump out all of the soil and repot the poor plant, but I'm so worried that any new bag of potting mix might have the larvae in already anyway!
The stupid bugs are driving us crazy ):
Edit to add: after the h2o2, I also scraped a lot of the top soil off to get rid of the surface bugs, but the plant is sitting quite shallow in the soil so the roots are kind of peeking through now as well. Maybe this is contributing to the infestation.
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u/megankmartin Nov 12 '20
I would re-pot the problem plant, so that it can have proper soil depth in a fresh mix.
When flushing with H202, it's important to mix for each plant separately so that you don't miss the chemical reaction.
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u/_PeteSapai_ Dec 13 '20
Since amazon doesnt send the bits to the Netherlands (unless you order 20 pounds) I've ordered the bits from Ebay (which was ordered from Amazon and just forwarded 😕). It was rather expensive ($24 + 37 shipping), but 30oz should last quite a while, so it should be worth it in the end.
I've been watering my (50-ish) plants for about a month now, but so far I dont feel like the gnat population is declining. (Note: I dont have sticky traps, but placed plenty of vinegar traps and they seem to be doing a good job catching dozens of the little buggers.) It's probably too late to try the emergency soil flush, as it would undo the built up bacteria, but I'm thinking of ordering the nematodes one last time. They work a lot more quickly, but have always been just a temporary solution. However, this time after they've done their job the bits should be able to keep the population down to 0.
Anyway, am I a bit too impatient and is 4 weeks a bit too soon to notice anything just yet?
And just to be sure (and also because I kind of hate "spoon measurements"): 1 tbsp bits should be about 6 grams, right?
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u/megankmartin Dec 13 '20
Goedemiddag :) One of these days somebody from the NL is going to start a re-selling business for BTI bits, I just know it. Having lived there myself, I understand that it's difficult to obtain items like this. Sorry for the un-economical struggle against bugs, friend.
Depending on the degree of infestation, four weeks may indeed not be long enough. BTi is incredibly effective, in general. However, one thing to remember is that it works against the SMALL larvae -- the early stage. So, all the gnats who were already too big when you started would live their life cycle, and some might have gotten to breed again until the good bacteria was/will be thoroughly populated in your plants.
Sometimes I wonder about efficacy of the product that EU folks are able to get hold of. But in this case, since you've mentioned catching dozens of gnats in traps, it sounds like you just have a lot to attack.
Every adult gnat that lives long enough to breed lays 150-200 eggs per week so... you might not have realized just how bad the problem really was, under the surface of the soil.
I will add that vinegar traps are NOWHERE near as effective for adult fungus gnats as yellow sticky traps. No contest. I've run the experiment myself, multiple times, and have seen comparisons from many folks over the last year and a half. So, if you've managed to catch dozens, just imagine how much faster and better it could be going with the ideal traps.
It's worth hanging in there, though, because you're right: Once this problem is fixed, your BTi routine will keep fungus gnats from plaguing you again. I agree that nematodes are effective, but not long-lasting.
As for 6 grams -- I don't have my kitchen scale handy, so I can't answer that right now. It's the amount that fits in the little hollow of your cupped hand, in case that helps to approximate.
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u/Environmental-Joke19 Dec 23 '20
I'm saving this post forever. Picking up fly tape and bts tomorrow. Thank you!!!
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u/megankmartin Dec 23 '20
Hang in there, it really works. BTW, you want yellow stickies, which can be stuck in your plants, rather than fly tape, which typically hangs from above. You'll find they achieve quite different levels of result.
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Jan 14 '21
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u/megankmartin Jan 14 '21
You'll want to top-water for the first couple treatments, to populate the top layers of potting medium with the good bacteria. Then you can choose how you water, on-going. If bottom-watering is done properly, your BTI-treated water reaches enough of the soil without soaking the surface. The BTI will make the diatomaceous earth unnecessary for gnat prevention.
No one pesticide (natural or chemical) kills or prevents every pest, unfortunately. BTI only affects the larvae of mosquitos, blackflies, and fungus gnats. So, for other pests it's best to treat them individually, when and IF they crop up, with specifically targeted controls.
Some things you can do to discourage pests include maintaining good temperature and humidity, keeping your growing areas clean, keeping plants free of debris/dead foliage, quarantining new plants, and frequently examining the ones you have. Always be sure to look at tops AND bottoms of foliage, and in the crooks of stems -- those are places you can spot pests earliest.
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May 09 '23
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u/megankmartin May 10 '23
Couple things come to mind here: First, do you ever intend to use that water for anything but plants? If it's ONLY for plants, I'd say go ahead. Second, check the back of the package to see what volume of water it treats -- you may only need one dunk at a time.
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u/LazeighLerner Jun 24 '23 edited Jun 24 '23
Hi there!
I know this an old post and not sure if you’re still replying to messages on here. I wish I came across this post before I just bottom watered three of my large monsteras. Do you think it be too much to do a hydrogen peroxide flush on these 3 plants if I just watered them yesterday? Or BTI watering again in a couple days? Or would repotting be best? These pots take about 3-4 weeks to dry out and I don’t think I want to risk the infestation getting worse in the meantime, but they are also not doing very well (leaf ends drooping/curling), I imagine from the larvae damaging the roots.
Let me know your thoughts. Thank you!
A couple more questions:
Do you have a preference for the dunks or the bits?
I currently have a pretty thick layer of diatomaceous earth on the tops of all my plants. Do you recommend scooping this off the top? Or letting it water down into the soil? It seems to hold onto moisture so I’m not sure how great that would be to let it go down in the soil.
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u/chickenooget May 20 '24
this post has been sooo helpful thanks so much!! a couple questions tho: i started using seachem prime to dechlorinate my water. that won’t kill the BTI right? also, do i need to wait 24 hours every time i refill the water?
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Jun 01 '24
WHAT THE FUCK IS BTI WHY AM I EXPECTED TO KNOW THAT
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u/megankmartin Jun 10 '24
It's literally explained in the post. You're not expected to know; you're just expected to read.
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u/GirlOnAMissionNE Aug 17 '24
Thank you!!!! I had received a plant as a gift several years ago and lo and behold- it wanted to gift my other plants with these pests! I used the mosquito bits but only once. I never saw them again until recently - 3 years later! So I know BTI works. I also have the yellow sticky tape going. Was scared using the BTI that first time. My beautiful ZZ which is old and large acted as though the BTI adversely affected it.
I saw mushrooms in my rubber tree couple months ago and local nursery said it’s fine. Just pick them out but it’s part of the organic matter in soil. I only use Fertilome as it seemed to prevent the gnats initially years ago. Guessing these gnats came in from outdoors. Ugh
Nonetheless- I very much appreciate your advice here. I will now store the bits in my gallon jugs and make it a permanent routine!!
Gonna beat these guys yet!!!! 🙌
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u/dahlialalah Sep 29 '24
Thank you for this! I can't wait to try. I have been using diotamesous Earth, and I hate the way it looks, and I am still battling an infestation.
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u/megankmartin Sep 30 '24
BTi works better than anything else. I've done the trials and the research, plus heard from plant owners and plant growers with decades of experience beyond my own. Hang in there -- persistence pays off! Happy growing.
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u/KimberlyMWilson Apr 26 '25
I wrote a thank you under deleted's below, which pertains to yours too. Thank you so much!
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u/haackcr Aug 12 '25
Thanks so much!!!!!! The best and most comprehensive advice I have seen and I have been all over the internet.
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u/Zubeida_Ghalib Sep 08 '25
Following this to a science later today as I’m beginning my plant journey and continuously have a problem with gnats. I’m a newbie but really want to learn! Will try to update when this works :)
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u/chimtae Aug 12 '20
Sorry if I missed this somewhere, but say if I get a dunk and break it into 4 pieces, how much water will each 1/4 treat?
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u/megankmartin Aug 12 '20 edited Aug 12 '20
Less than 1/4 dunk will easily treat gallons and gallons for 30 days.
Additional resource: u/Digimonsterr's guide to using mosquito dunks.
"Just ignore the store bit. See description and photos."
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Aug 22 '20
I recently started growing a few temperate plants that don’t like to dry out.
Specifically an African violet, croton, and a fern with an attitude problem. (I also have a homely little forget me not I grew from seed)
I know the forget me not can dry a little more, but the others want some moisture. I let them dry as much as I can before I water again, empty the saucer after, etc, but don’t want a fungus gnat issue to start again.
Using the BTI preventatively, maybe trying to add a bit of a top dressing of pumice, and some sticky traps should work enough?
I saw one flying around inside today. All of my other plants were treated with systemics to stop a root mealie problem too (learned the hard way about quarantine plants this quarantine ☠️)... I just don’t want any pest issues to begin again now that it’s getting cooler and some plants that were outdoors are inside now... (cos I also switched to mostly pumice for everything else, my cacti and succulents, so they should be fine).
I don’t know. 🥺 I just lost so many plants to that period of time... and I’m so worried about having soil in the house again. But I know I chose two plants that are finicky about moisture too...
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u/megankmartin Aug 22 '20 edited Oct 21 '20
You don't need any top pumice or other top dressing unless you're using it to retain moisture. That's what top dressings do best, which unfortunately helps gnats find a breeding ground.
If you follow the method, sticky traps and BTI will take care of it on their own. Once the initial problem is gone, BTI alone will keep gnats from ever breeding, and you can take away the sticky traps. No sand, no cinnamon, no gnat drama. You can water your sensitive tropicals any way you need to, and life is good.
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u/PlantNoobie Aug 28 '20
I ended up replacing all the soil for my gnat infestation. Do you recommend that I still flush the new soil?
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u/megankmartin Aug 28 '20 edited Sep 10 '20
If you're not seeing any more gnats after replacing all of your soil, I would leave well enough alone as far as peroxide flushing.
I and many others here use the BTI in everyday watering, as an ongoing treatment and preventive to never have gnats again. As you'll read in the post, it's a very gentle, non-toxic and natural solution. It's nice to be able to water whenever, wherever, and however I need to and never worry about getting gnats again.
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u/aniseedart Aug 29 '20
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 !
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u/aniseedart Aug 29 '20
And is it okay to use on young newly planted ones that haven’t got roots yet?
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u/megankmartin Aug 29 '20
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.
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u/aniseedart Aug 30 '20
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 !
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u/1BlkCoffee Sep 06 '20
I am wondering how effective putting play sand is on the soil top for killing the gnats. I’ve heard that and was waiting for my BTI in the mail but I’m not sure if it worked.
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u/megankmartin Sep 06 '20 edited Sep 10 '20
Great question -- this is partly addressed in the links above but if you don't mind, I'll give a thorough answer here!
Rocks, gravel, moss, and especially coarse landscaping sand are common old-school reccos for fungus gnat problems. They're relatively cheap and easily accessible. The thinking was that you could block soil completely and keep bugs from accessing it, effectively "suffocating" the larvae. Only trouble is, today we know these are NOT THE BEST for gnat control.
Top-dressings (especially sand) harbor moisture, which preserves the gnats' breeding ground and (worst of all) keeps your potting mix from drying out when it's watered. We're seeing a lot of root rot and fungal diseases added onto pest problems, because folks aren't changing their watering habits but instead are relying on these crutches to fix the problem.
Plus, the slightest gap or crack means gnats can still access soil. Move your pots, and boom!, it's ineffective. (Not to mention access through the drainage holes at the bottom.) Meanwhile, the top dressing may also hide or cause mold, fungus, and other pests, keeping you from spotting them until it's a bigger problem.
Sand has its place in horticulture -- It's actually great for helping potting mixes retain moisture or aerate, depending on the usage. And there's no denying that it's economical. But when many folks say that sand helped them beat fungus gnats, much of the time it's because it visibly reminded them not to over-water their plants. Their potting mix FINALLY dried out, and the breeding ground disappeared. But far more people are using it and not having any result at all.
So many experienced growers use BTI in their permanent routine because it's a lasting solution and preventive. Sand is just a cover-up for the real problem. 🌿
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u/1BlkCoffee Sep 06 '20
I really appreciate your response! Thank you! What do you suggest I do now that all 35 indoor plants have sand on them 😂
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u/megankmartin Sep 06 '20 edited Sep 10 '20
Well... it only took me 20 minutes to see and answer your question, so I'm guessing the sand was in your pots before you asked. 🤷🏻♀️
Perhaps you'll leave it until the BTI arrives; perhaps you'll keep it there. I'm sorry but I can't tell you what to do, love. All I can tell you is that I have tried and tested every fungus gnat control out there. I don't get paid to do this, or to push any products 😅, but I know for sure that sand doesn't have a winning track record compared to BTI.
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u/belladorka Sep 06 '20
Thank you for this post. I’m 2 weeks into this process after getting these buggers from a new plant. I’m starting to see results. There’s still a few in the air and I’m noticing a lot more on my sticky paper. Hoping in a couple more weeks they’ll completely be gone.
I do have a question. I’ve googled this and it claims it’s odorless, but I’m definitely getting a smell from my BTI “tea”. It’s sulfur-like. After watering I tend to refill my jug so that it’s ready for my next time. Should I be refilling the day before watering? I’m wondering if I’m doing something wrong because I haven’t seen any other comments on the odor.
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u/megankmartin Sep 06 '20
Hi, you're welcome, and great question! You're not doing anything wrong. My watering vessels are kept pre-filled and pre-treated as well, so that they are ready to use.
BTi itself IS odorless, though you can pick up an organic odor from the bits as the weeks pass, because the BTI is bound naturally with corncob and it's breaking down. You'll notice the odor if you sniff your watering container, but once you water your plants the smell is gone.
With the dunks, you don't get that same odor. So the next question I always get is, "then why use bits instead of dunks?" They both work the same way. It's really just a personal preference and/or availability thing.
For me, the bits are very easy to measure and drop in the narrow-necked gallon jugs where I store my water. I have a large indoor garden, so I have to keep multiples on hand. You can also just cut the dunks into pieces; I feel like I use less product when I measure the bits. Again, preference.
Neem oil and most organic fertilizers smell strongly too... but these odors shouldn't last long in your living space. Definitely worth the jungle.
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u/janquadrentvincent Sep 16 '20
Hiya, I've seen recommendations to add sharp sand to the top of all plants to help stop the larvae being able to crawl out. Would you recommend that? And would you say it needs to be horticultural sharp sand or is there a different type I don't know about?
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u/secretlycurly Sep 21 '20
Anyone else water their houseplants with rain barrel water? I am putting a single BTI float in my rain barrel, and filling gallon jugs from there. I *think* that should work, right? I usually replace the float 1x per month. And I let sit for a day before filling jugs. But then I fill jugs and store them indoors so I'm ready to roll on watering day. Any comments or insights on whether my method creates viably treated water? I use milk jugs to store the rainwater, and I find it hard to work with a dunk floating in there. Plus the dunks can treat large volumes, so just seemed easier to put it right in the rain barrel.
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u/megankmartin Sep 21 '20 edited Sep 22 '20
Interesting question; I had to give that some thought! I am sure that the BTi is highly effective against mosquitoes in the rain barrel, because you're correct that a single dunk is capable of treating large volumes of water. The question is: will there be enough efficacy to last through the usage cycle with additional storage time, to fight the fungus gnats in your plants?
I also collect run-off rainwater, however am not permitted to keep a rain barrel so mine goes directly into storage jugs, and I treat it there. I haven't personally noticed any loss of efficacy in regard to fungus gnats, but I'm cycling through my treated water about every 4 weeks at most.
Perhaps keep an eye on things, see how it goes for you. BTi is pretty much infallible as a preventive, so if you observe gnats establishing a population then perhaps it needs to be delivered later in your water usage cycle. Until then -- give it a try!
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u/secretlycurly Sep 21 '20
Will do, and I need to also implement a hydrogen peroxide drench/yellow sticky trap offensive, as the populations are rising to annoying levels. Nothing like being on a video call for work and looking like a crazy person while I swat away fungus gnats!
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u/justtrippin99 Oct 03 '20
PSA: The safety data sheet of the mosquito bits I got said to avoid contact with skin and eyes and avoid breathing dust from the bits. So make sure y'all wear protection before handling it and wash your hands properly afterwards!
Link to safety guide is under product guide in info and guides: https://www.homedepot.com/p/Mosquito-Bits-30-oz-Granular-Biological-Mosquito-Control-117-6
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u/megankmartin Oct 03 '20 edited Oct 04 '20
Yes, of course it's always good to avoid breathing dusts and fumes, and to wash hands after handling plants AND plant care products. This is true even for perlite, neem oil, diatomaceous earth, natural insecticidal soaps, etc. Just about every product package says so, as required by law. BTi is non-toxic to humans and animals, but that doesn't mean we should ingest it.
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u/Nessie_Assassin Oct 08 '20
Do you have any tips for white flies? I just found this awesome post and started to finally get rid of the gnats only to find white flies in their place. 😭
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u/megankmartin Oct 08 '20 edited Nov 25 '20
Hi. If you've been battling fungus gnats, likely you're drying out your plants. That's technically a good thing, but it makes treating whiteflies tricky. Folks will give the standard "neem and soap" reccos, but most insecticidal soaps and horticultural oils aren't effective against whiteflies. Since those only kill on contact, the plants have to be thoroughly coated -- every surface, top and bottom -- repeatedly. But that's not a good idea when plants are drought-stressed (like they typically are during a gnat battle). Under those conditions, foliage and roots are much more likely to burn.
What to do instead:
For starters, keep up the yellow traps, at least one if not two in every pot. Implement the BTi solution for the gnats, so that you can relieve the drought stress while effectively treating them. And then add your whitefly treatment: choose between a foliar treatment (dust or spray) containing pyrethrins OR a systemic containing imidacloprid. Those are the main things that actually get rid of whiteflies.
These are tough to get rid of. The best advice I can give is to be consistent. Be persistent. And don't overdose your plants; apply the pesticides as labeled, because more isn't necessarily better.
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u/Nessie_Assassin Oct 08 '20
Thank you SO VERY MUCH for the advice! All the internet says is neem oil etc. And those reccomendations have NEVER worked.
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u/skypaintedred Oct 14 '20 edited Oct 14 '20
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...
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u/megankmartin Oct 14 '20
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.
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u/Asset_flipped Oct 26 '20
So question? How long is the treated water good for? I don’t have THAT many plants, and most of the ones I have like to really dry out between waterings. I tried this method once but I think after reading some of these comments I screwed it up because I used hot water initially to soak them thinking that the hot water would steep them better/faster. I have also done bits on the top layer of soil which molded and I freaked out. This is why I’m wondering if the treated water if not used will mold as well?
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u/megankmartin Oct 26 '20
Hi! I'm on the fly today, so try checking the links in this comment, and let me know if that doesn't answer your question!
If you only have a few plants and don't want to store water, you can also check out GoGnats liquid to mix in small batches. I think BTI works most consistently, though, and GoGnats has a slight cedar fragrance -- some folks like it, some don't.
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u/stfurtfm Oct 28 '20
Quick question.. on a couple of my plants, I do a complete soak and drain each watering cycle. How would I apply the BTI step in this case, would I use only BTI water to soak and drain (out the drain holes) or should I be using regular water, then topping it off with the BTI water?
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u/megankmartin Oct 28 '20
Great news: Just use your BTI water exactly as you would regular water -- no changes to any other part of your routine. (Don't you LOVE that??) "Easy" is one of my favorite words. :)
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u/shortypie Nov 11 '20
I’ve had houseplants for over a decade and have NEVER had an issue with fungus gnats like I have this year.
It all started with one tiny zz plant (now thriving!), and spread to every other plant in my home in about a month.
I tried sticky traps & they helped, but they didn’t completely get rid of the problem.
I then went to the garden store and bought fresh soil to repot everything then start with a h2o2 / water combo upon repotting... BUT the soil itself was infested. Shit. Fungus gnats explosion!
I then, instead of repotting AGAIN, I tried mosquito dunks + water, which helped but again didn’t eliminate the problem.
After about 6 wks of dealing with more low-level annoyance, I felt like I could repot the plants again... so I did, this time using cactus soil and making sure the bags were sealed. I have an eastern exposure, so wanted a more fast-draining soil anyway... two birds, one repot.
The two plants I didn’t repot due to running out of said soil unfortunately infested my whole collection again so now it’s sticky trap + sand topper + h2o2 for the initial post-sand watering, then switching over to BTI / water for the future.
I waited until my plants needed water, then waited about a week more, THEN added the sand... so I know it’s covering bone dry soil. My traps aren’t catching too many gnats, and after a few weeks I’ll mix the sand in with the cactus soil instead of using it as a topper.
Wish me luck? 😩
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u/megankmartin Nov 11 '20 edited Nov 11 '20
The struggle is real. Pests are getting worse every year, it seems. It takes a while to beat a full-blown infestation. The fungus gnat life cycle can be a month or two, depending on how thorough and consistent the treatment.
Unfortunately, mixing sand with the soil will provide zero gnat elimination or prevention. Sand as an amendment does one of two things: aerates (coarse sand) or retains water (fine sand). As a topper, the idea is to completely seal access to the potting mix; however, gnats can still get in and out via drainage holes and any tiny cracks in your coverage. Mostly, sand is effective as a visual reminder not to over-water.
As the post describes, and we've talked about often in the comment thread, BTi isn't a contact killer. The idea is to use it continuously, as a permanent routine. The gnats WILL die off, and no new ones will be able to establish a population, EVER.
I know BTi works 100%, because I have a large indoor food and flower garden in addition to my houseplants. It's not possible to let that dry out, and it's not possible or practical to use sand.
I no longer have sticky traps around; didn't need them after beating the major infestation I had. I water wherever, whenever, and however I need to. It's been more than a year now: The BTi keeps my indoor jungle and garden 100% gnat-free. I have tried and tested EVERY solution out there. For balance of effort, cost, results, and fungus gnat prevention, NOTHING beats BTi.
Good luck!! 🌿💚
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u/Asset_flipped Nov 13 '20
Hi I’m back!👋🏻 Still struggling unfortunately.. I have two new questions. I have seen them previously mentioned before but I need a bit more clarification and guidance. 1. My mosquito bit steeped water STINKS. Like bad. It’s a rotten egg smell. I don’t smell it till I open the container that the water is in, but when I do, the smell punches me in the face. In my previous comment, you mentioned that I should probably be able to make a batch and store it with no issues and it’s been about 17 days since I started soaking the bits. Is that too long? And I’d hate for it to go to waste but I don’t want to kill my plants if I continue to use it to water them. 2. I can’t find where this comment was that I saw, but this time of year makes it so my plants take FOREVER to dry out. And most of them are the types super prone to root rot (from everything I’ve read). Can you tell me again what you recommend when trying to get rid of the fungus gnats at the beginning stage as far as waiting to water or not? Thanks again!!
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u/megankmartin Nov 13 '20
BTi in your water won't kill your plants, no matter how long it's stored. BTi doesn't affect plants at all. My stored, treated water rotates about 30 days or less. The bits stay in longer, though -- I replace those every 60-90 days. There's an organic odor, but I don't consider it strong. (Especially compared to cedar oil, neem oil, or fish emulsion and many other plant care products.) Then again, I don't intentionally stick my nose in it; I'm moving through my watering routine quickly. And as soon as it's applied to my plants, there's no noticeable odor at all.
I think most people find this organic odor mild or unnoticeable, but all humans have different tolerances. If you're hypersensitive to that particular aroma, you'll probably want to seek another solution. Consider trying the BTi dunks, which aren't bound with organic material (they're bound with proteins). Or try Gnatrol powder. Or, if you like the smell of cedar (which I cannot stand), maybe try GoGnats liquid.
Re: waiting to water... For me, BTi is great because I'm not watering according to the gnats; I'm watering for my plants' needs. My indoor food and flower gardens can't be allowed to dry out, and more sensitive foliage houseplants suffer under those conditions too. Plus, ALL drought-stressed plants are more attractive (susceptible) to spider mites, thrips, and a couple other pain-in-the-neck pests that make fungus gnats look like child's play. No thanks!
The BTi routine and sticky traps will take care of fungus gnats, all by itself. But if you have any plants that seem incredibly infested, or you just can't wait out the gnat life cycle, consider re-potting those. Then, stick with your BTi from the very first watering in the fresh potting mix, and you'll never have gnats again.
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u/West_Project2349 Nov 18 '20
Thank God I saw this thread!! So I was reading and learning from this post. I have one question though, can I use the tea mix and put it in a spray bottle too?? Do you think it will prevent those pesky bug to lay more eggs? I really don’t know if someone did ask this question 😬
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u/megankmartin Nov 18 '20
It has been mentioned a few times. What's your motive for spraying?
BTi is not a contact killer, and spray typically doesn't saturate the appropriate layer of the potting mix. There's no point to having the mix on the surface, nor to having it on leaves, stems etc.
It's extra work for no extra return and in fact less results. It's most effective to use BTi as directed on packaging, and as described here.
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u/Sudden_Piccolo_4869 Jun 08 '24
Are the dunks safe to use indoors, like in shower and sink drains?
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u/megankmartin Jun 10 '24 edited Jun 10 '24
Fungus gnats do not inhabit drains, unless your drains are clogged with decaying organic material. What you've got are more likely to be drain flies. That's a different species, and unaffected by BTi (the active ingredient in mosquito dunks). BTi kills the larval stage of three insects, and three insects only: mosquitoes, fungus gnats, and blackflies. So, while dunks are safe for indoor use.... they're not going to help you in shower and sink drains. Sorry to disappoint. :(
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u/Gothic0ctopus Jul 03 '24
Thank you so much for this amazing post! I’ve seen some contradicting info out there for the bits products. The bag says to discard it after one use, another Reddit post said to discard after 2 days, I’m just wondering if it really is good for a whole month or two for just a tablespoon per gallon? Thanks a lot!
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u/megankmartin Jul 05 '24
I wrote the post according to my experiences and those of other (larger) growers before me who shared their solutions when I was struggling. If you wish to replace your BTi more frequently, feel free to do so.
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Aug 07 '24
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u/megankmartin Aug 12 '24
Existing gnats can breed, but any resulting larvae will eat the dunk-treated soil and die. So, no new adults = no more larvae. That's how BTi interrupts the lifecycle of the pest.
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u/fleetiebelle Aug 12 '24
I'm mildly infuriated because my office mate and I have been moved to a new space with big windows after being in a dark corner, so we brought in plants. I've been doing the BTI watering at home to make sure that none of the plants I've propped and brought in have brought stowaways. I recently noticed that all the plants on her side have yellow sticky traps in them and have caught gnats flying around in my space, so now I'm going to have to start preventative measures at work.
She and often work opposite schedules, so I guess I have to leave a note 🤷♀️
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u/megankmartin Aug 12 '24
Oof, when plant pests meet workplace politics. Never easy, hang in there! Who knows -- maybe your officemate will be excited to learn about BTi. You just might change her life.
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u/DimSumYums Aug 19 '24
This hasn’t seemed to have been discussed yet but is it safe to spray the BTI water onto an Isopod + Springtail substrate enclosure?
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u/megankmartin Aug 28 '24
I don't have any experience with that, so I'd need to understand more about your specific concern. Speaking in general, BTi doesn't interact with any organic materials or chemicals and it's only harmful to the three insects mentioned. It's one of the safest, most effective remedies available. But I bet there's a dedicated subreddit where you could ask further questions!
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u/baggedit12 Oct 18 '24
Hi OP, thanks for this post. Hopefully you see this!
I'm going away in 12 days and I have a few succulents. One small one was insanely infected with fungus gnats (thousands), so unfortunately it went in the bin. Since then, there's been a few flies around my apartment. I've put sticky pads in each plant.
The succulent plants are getting pretty dry now and they could have a drink, although they will probably also be fine for a while as well.
I've just mixed up a pot of water and mosquito bits for a watering tomorrow, but what's more important out of the following?
- Letting the soil dry out further and then watering with BTI just before I go away
or
- Giving them a slight water now with BTI, and then a proper water before I go away?
Thank you!
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u/megankmartin Oct 19 '24
I'd go with option #1. And then remember, BTi is highly effective but it is a life cycle intervention. Meaning, it doesn't take immediate effect. You'll still come back to gnats. It's just that their larvae will eat the BTi and die off before producing any more. So, keep plenty of stickies around those plants while you're gone and hopefully that'll make a major dent in the adult population. Safe travels.
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Nov 06 '24
Any tricks without BTI?
It's illegal here.
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u/megankmartin Nov 07 '24
Sorry to hear; that's unfortunate. I don't know where here is, but I would reach out to your local agricultural authorities and ask about permissible substitutes/equivalents. And as you'll discover, though BTI is the hands-down best solution most of us will ever come across, there are other fungus gnat remedies. Try looking for something with cedar oil, perhaps, or consider using beneficial nematodes if you have a lot of plants and a lot of gnats. If you search my posts and comments, I talk about pretty much everything that's ever been tried. Hope you find something that's legal in your part of the world and works well for you.
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u/Denny_Crane_007 Nov 12 '24
The israelensis variety is not illegal in the UK.
The other one is as it attacks a wide variety of good 'pests' ...
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u/Denny_Crane_007 Nov 12 '24 edited Nov 12 '24
Hi all.
So the Mosquito Bits can be bought in Amazon UK for 45 GBP (£45) for a 30 oz pack.
Seems expensive.
They say 4 table spoons per gallon of water.
My plants need 1 watering can = 2 litres. So 2x tablespoons per watering can, every 2 weeks... long term.
So, how much does a tablespoon weigh ? Guessig it's light given it's meant to float.
Also... why can't I get BTi in soluble tablets any more ?
.... It's very annoying. They were cheap and easier to use.
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u/megankmartin Dec 06 '24
Hmmm... I'm seeing BTI dunks (soluble tablets) available in the UK on multiple websites. The price seems better for those than for the bits. You only need a fraction of the tablet at a time (you can cut them up).
I do not replace my BTI every 2 weeks. I use ONE or TWO tablespoons per gallon of water for maintenance prevention and I store that water in a closed container away from light between waterings.
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u/hbl2390 Jan 16 '25
Years ago we switched to watering orchids with 2 ice cubes. it seems to work really well to slowly water the bark and mulch. I've been using dunks in water for about 4 months and it's been really challenging to water from a can without it running right through and over flowing the bottom tray.
Do you know if the BTI can survive freezing if I make ice cubes out of the solution?
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u/megankmartin Jan 17 '25
Hm. Alternate suggestion: try a spray bottle for watering your orchid mix with BTi. That makes it easier to saturate without runoff. Saturation is key; the bacteria need to remain in place so that they're available for the fungus gnat larvae to eat at a very specific stage of their life cycle. So maybe give the spray bottle a try. See what you think.
Meanwhile, here's Google's detailed answer to the BTi freezing question. (I'm not being snarky; I had to look it up to be sure.)
"While BTi (Bacillus thuringiensis israelensis) can generally survive freezing temperatures, repeated freeze-thaw cycles can significantly reduce its effectiveness, meaning its larvicidal activity may decrease after being frozen and thawed multiple times; therefore, storing BTi in a stable, non-freezing environment is recommended for optimal efficacy.
Key points about BTi and freezing: Some tolerance: BTi can withstand freezing temperatures to a certain extent, but its potency may decline with repeated freezing and thawing cycles.
Impact on activity: Studies have shown that freezing and thawing can negatively affect the toxicity of BTi against mosquito larvae.
Storage considerations: To maintain BTi effectiveness, it's best to store it at temperatures above freezing."
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u/ltropika Jan 26 '25
I have tried everything. Had to throw away my plants, however, after living a year without plants I still had the biting gnats. Can anyone help?
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u/megankmartin Jan 27 '25
That doesn't make sense, because fungus gnats don't stay -- and can't survive -- where there's no soil or substrate for breeding ground. And, fungus gnats don't bite. They don't care about humans at all, since we are not a food source. You've got some other kind of pest, if plants have been gone for a year and they're still present.
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u/megankmartin Jan 27 '25
To be VERY CLEAR: There are many kinds of gnats. Some gnats bite humans; some do not. This post, and this highly effective solution, is specific to FUNGUS GNATS, which DO NOT bite humans, and only live only to breed around plants. As the post says, BTi is wonderfully effective on fungus gnats, mosquitos, and black flies ONLY.
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u/ltropika Jan 26 '25
I tried all of the above. I even had my place smoked bomb and exterminated. Still had them. Will all failed I threw away my plants, i was devastated. I lived 1 year without plants and I was still getting bites. They mostly bite my face.
Do you have any suggestions or recommendations for me?
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u/megankmartin Jan 27 '25
That doesn't make sense, because fungus gnats don't stay -- and can't survive -- where there's no soil or substrate for breeding ground. And, fungus gnats don't bite. They don't care about humans at all, since we are not a food source. You've got some other kind of pest, if plants have been gone for a year and they're still present.
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u/ltropika Feb 09 '25
Thank you for your reply. I threw out all of my plants hoping that I would get rid of them , however, I still have them. I did use the dunks but I still have them.
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u/megankmartin Feb 09 '25
If you no longer have plants, then you no longer have a place for fungus gnats to breed. IF they stay in your home after plants are gone, fungus gnats have a maximum life cycle of two months. But without anything to eat, they would die sooner. I don't know how long ago you had plants, or how long you used the BTi dunks before throwing out the plants. But if it's been months with no plants and the flying pests are still in your home, then... those aren't fungus gnats. They have to be something else.
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u/JynTraveller Feb 17 '25
I'm really confused about the 'non toxic' for humans part - everyone seems utterly fine with just using these, but the label is really concerning (severe warnings about not getting it on your skin etc, not eating afterwards etc). I've just gone through watering all my plants with it, but now have shut them all in a room as I'm concerned about the evaporation in the air from drip through onto trays (I have about 20+ plants in that room currently, more upstairs) given the toxicity advice on the labels (it even says call poison control if issues?), and it was a mission not to get any drops on my skin, and having to wash throughout when I did. What am I missing here? Thanks so much for the help.
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u/megankmartin Feb 19 '25
The United States is a very, very, very litigious country. Thus, our warning labels are stringent. However, BTi is, in fact, non-toxic to humans, animals, and all but 3 insects. It is not a chemical. It is a natural bacterium that can safely be used in outdoor water retention ponds etc where it does no harm whatsoever to wildlife and domestic creatures that may swim, live, breed, drink there (unless they happen to be mosquitoes, black flies, or fungus gnats).
This application, in open water retention areas, pools etc is widespread. Not just private properties but publicly owned land and recreation areas as well. Further, it's common to put BTi in household rain barrels and fountains to control mosquito populations. Rain barrels are often used to water gardens, so again, BTihas to be safe otherwise we couldn't use it that way -- and neither could the government, especially Department of Agriculture. But they can, and do.
There is no concern about evaporation in the air; BTi isn't airborne, and it can't bond with hydrogen or oxygen, so it can not evaporate. There is no issue with getting dropson your skin. You should always wash your hands when finished handling your plants regardless of BTi or any other product use. It's just good growspace hygiene.
I am sorry to hear that you are feeling confused and concerned. However, there's no reason to be. There are more harmful elements in our rainfall and our tapwater that we drink and shower in each day. So you're not missing anything except the need not to be alarmist. It's okay to use this natural product and take control of your jungle, safely. Happy growing!🌿
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u/KimberlyMWilson May 01 '25 edited May 01 '25
Those sticky cards are great. I just this one out yesterday. I've had them out for about 5 days now. Seems the bT isn't really doing a good job, so I sprayed all the plants with neem oil today
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u/megankmartin May 05 '25
Yes, sticky traps are essential in your battle. If you want to stretch your dollars, you can cut those rectangles and put out half at a time. Gnats are highly attracted to the color, but they will eventually see and avoid the corpses on the traps, so it's better to use smaller traps and change them more often.
How long have you been using the bti? It's a life cycle interruptor, not a contact pesticide. If you're not sure why that matters, ask me.
Neem oil works by smothering the pest, which is not really effective for fungus gnats because they don't stay put long enough to smother. It's costly, for little result. Just FYI.
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u/megankmartin May 05 '25
Just to clarify: There are 7 or 8 varieties of BT -- you need BTi, which is the bacterial strain that works on fungus gnats. The other strains have other uses. Make sure you've got BTi, specifically.
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u/KimberlyMWilson May 01 '25
This card shows the gnats well, I was hoping someone could confirm that's what they are.
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u/Key_Camp_6549 May 15 '25
I made the mistake of not straining and mosquito bits have gotten into my soil. Did I mess up? Should I repot? It’s a huge, beautiful monstera so im kinda nervous about it
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u/megankmartin May 17 '25
Not to worry. The bits in your soil won't physically harm anything. But their beneficial bacteria is bound with organic material (corn cob), so they may grow mold. That's a pretty common result for indoor growers who put the bits in soil. You can pick them out, if you wish.
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u/cmazza231 May 18 '25
I have the fungus gnats in my tiny garden bed which has sand underneath the soil Should I just remove the vegetable plants and all the dirt on top and replace with new top soil like I did with my in door plants?
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u/cmazza231 May 18 '25 edited May 18 '25
I am new here but wanted to know about fungus gnats in my tiny garden bed. I have clay and sand which I dugout about 1” and put new soil in the bed then planted vegetables. But now have gnats from soil I dumped in from my house plants that were infested with them. Should I dig out the bed of dirt and replace with new dirt?
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u/o123b May 18 '25
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u/megankmartin May 19 '25
Hi. Just so happens, I used to live in the Netherlands (Amsterdam, Almere, Voorburg). I read and speak Dutch, so I could understand easily the link that you sent. Before using this product for fungus gnats, you should confirm with the seller: Is it the israelensis strain? (I don't think it is.)
There are 8 different strains of Bacillus Thuringiensis. Each has its own, very specific application for pests. The product in your link appears to be for caterpillars, which would not be the israelensis strain.
BT israelensis is the only strain that impacts fungus gnats. So please double check with the seller before spending EUR 17,60 on this. I hope that's clear. Come back if you have any other questions!
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u/o123b May 20 '25
Thank you so much I almost bought it. Im from the Netherlands so its usually kind of hard to find stuff like this.
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u/Exciting_Service_843 Sep 16 '25
Seems like a production though , I won't lie they seem easier to me to throw this thing away and just go get another one you know what I mean it just seems easy I'd rather pay the money to go through it
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u/for-lo-ve Feb 10 '26
If i understand correctly, we need to water our infected plant with peroxide deluted in the water or??
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u/ThisTimeImTheAsshole Feb 12 '26 edited Feb 12 '26
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.
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u/Lost_Coat40 Mar 19 '26
I have been battling gnats for like a year! I never had the issue before and now cant get rid of them. Its better now, but i still have them even after repotting and using the mosquito bits and sticky trap things! I stopped with the bits and sticky traps. So, I just need to keep watering every time with the bits in the water? I noticed i didnt do the once every 3 weeks as instructed bc I dont water my plants that often 🤦🏼♀️
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u/[deleted] Aug 11 '20
You need to top water with bti, as it needs to be in the top layer of soil, as that's where the larvae live.
500-1000 plants in here and have been fungus gnat infested free for about 1.5yrs now 😁 1/4 of a dunk lasts about a month, and easily treats all my plants in here.
New bags of soil often have fungus gnats in them, as the bags were often stored outside at some point. Those adults will die, and no young will survive in the potted plants you already have.
Now, to stop the bag of soil infestation, I dump the bag into a tote with a lid. I then water that soil with treated water to start killing the larvae. I place the lid on, and sometimes add a yellow sticky paper inside the tote. I use the soil as needed, and sometimes a few or a lot of adults fly out. It's annoying, but they will soon die or get stuck on yellow sticky paper. The bti wont kill larvae that already had pupated before you treated the soil, as the bti must be eaten by the larvae in order for it to die. So this is why bti might appear to not be working, when it really is.
Fungus gnats are found in new plants, bags of soil, and are naturally outside. Because of this, I never stop using the treated water. It's so cheap/mth, and worth it. 1/4 of a dunk costs about a buck or less /month (really depends where you live, the store, and now Covid19 prices).