Often considered only a minor houseplant pest, fungus gnats can quickly become a major issue if an infestation gets out of hand. Here’s how to identify, get rid of, and prevent fungus gnat infestations in your plants.
What are Fungus Gnats?
Fungus gnats are a fruit fly–sized insect pest that primarily affects indoor houseplants. Attracted to the moisture of potting soil, adult gnats lay their eggs (up to about 200) on organic matter near the soil surface. After about three days, the eggs hatch into larvae, which burrow into the soil to feed on fungi and decaying plant material. Two weeks after that, adult gnats emerge from the soil to repeat the process. Adults live for about one week.
Fungus gnats are completely harmless to humans, since they can’t bite and don’t spread diseases. They can be a problem for houseplants, however, when their population explodes and their larvae starts to feed on plants’ roots. Fungus gnats may also spread Pythium, a group of plant pathogens that causes “damping off” in seedlings.
Once you have a fungus gnat infestation, using consistent management and prevention techniques is key to ending it. Further down on this page, we’ve listed a few of the best ways to both get rid of adult gnats and prevent new gnats from emerging.
Table of Contents
1. How to Identify a Fungus Gnat
2. Fungus Gnat Damage
3. How to Get Rid of Fungus Gnats
4. How to Prevent Fungus Gnats
Reader Comments
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Fungus gnats
Many years ago when " My Big Fat Greek Wedding" was new, i used Windex to kill scale on my aloe. I used it again on the soil when my plants got fungus gnats. It works. Spray the soil & any bugs who are disturbed every couple of days. The movie was right- it works for everything!!
Fungus Gnats
This is a terrible article. Sticky paper? Really? Apple cider vinegar? Really? I was hoping for something a lot more insightful coming from Farmers Almanac, but you gave me sticky paper.
How about this… For fungus gnat prevention, cover your topsoil with sand, or small pebbles. This prevents the adults from being able to burrow into the organic soil to lay their stupid eggs. Boom! Problem solved!
I’ve also heard that pepper sprinkled on the topsoil works, but I can’t verify that. I’ve tried it, but without knowing how much or how often, I’m not sure I did it right.
Now… my problem is that the gnats have infested the soil I blended for my succulents. I thought it would be safe due to the high ratio of sand that went into it. Unfortunately, it was not. Fungus gnats have infested my flat of baby succulents & I need to know how to get rid of them.
This article was a lot less than I expected. Disappointed.
Fungus Gnat Solutions
A layer of sand, small gravel, or even perlite can help to prevent adult gnats from accessing the soil from above, but it needs to be a relatively thick layer (at least ½ inch) and doesn’t prevent them from getting in through the bottom of the pot.
We’ve had the most success using a combination of sticky fly traps to capture the adults and water treated with mosquito dunks to kill the larvae in the soil.
Gnat larvae
I heard one part peroxide to four parts water kills larvae on contact. Don’t water too often with this though I do it every other time I water my plant.
Rubbing Alcohol
Plain, drugstore 70% isopropyl rubbing alcohol sprayed on the surface soil has worked for me. Not sure if it would hurt the plant to water immediately after, but I've always waited a day to water after spritzing on alcohol. I don't get these gnats very often, but when I have, rubbing alcohol has always worked.
FUNGUS GNATS
Oh Lord I got them from re-potting a houseplant. They must have been in the new soil. I used the yellow sticky traps and made water from mosquito bits. I almost have them under control. Now I have another plant that needs to be re-potted. So I have potting soil baking in the oven at 400 degrees. After it cools I will feel safe to use it. These things are a hot mess!!!!!
Fungus knats
Tried and true...did it many times.....DE foiliar spray slurry knocked the he'll out of aphids and white flies also......eliminates them quickly......my infestations started prior to flowering, ergo most of the "dirty leaves are gone before harvest.....I'd rather not spray buds with all that particulate (probably would wash up nice) . Be sure to cover soil when spaying so pests don't fall in substrate.
Fungus Gnats
I tried all those neem oil and stuff. The only way I got rid of them was to take out two inches of soil in the pots and replace it fresh soil. Worked, and haven’t had a problem since.
Getting Rid of Fungus Gnats
A surprisingly easy method I heard about a few years ago & have used successfully ever since is Mint Tea. Specifically, mint tea bags. I brew my usual pot of mint tea, using 3 tea bags, then place the (slightly) used tea bags on top of the soil in my indoor pots (& I enjoy drinking a pot of tea). Some recipes call for you to brew the tea & drench the soil with it, but I've found putting the tea bags on the soil works continuously & effortlessly. Just dampen them every time you water your plants & you have constant mint aromatics that the gnats do not like & they disappear. You can replace the tea bags (or just let them compost into the soil...) as often as you drink pots of mint tea.
how to simply rid your plants from these pests
I found that a light sprinkling of Diatomaceous earth on the soil and a misting of apple cider vinegar kills adults and babies. It doesn't damage the plants and the smell quickly goes away. No traps just d. earth and the all trust-worthy a.c. vinegar.
Gnats
I moved into a house that had been vacant for about 2 years. There were the usual spiders and other bugs, there were also interactive cat toys (aka mice). So I called pest control to come out and spray for the bugs and set up mouse traps that would be safe to use around my cats. Well the cats seem to have taken care of the mouse problem. When I went to go pick up the mouse traps, I noticed it was all sticky stuff and they were covered with gnats, flies, spiders and my arch nemesis - Stink bugs. Shame on me for not asking to see the traps before they were set because I would not have allowed them to be put out, I wanted traps that I could bring the mouse outside and release it.
So if you know you don't have a mouse problem but want to get rid of bugs this might be the trap for you. The pest person said these traps have a scent that would attract mice. I also use the cider vinegar traps and they work well. I tried the tape traps for the gnats and that was a total fail. Someone suggested that I spray some flowery scent on the tape. I moved and the plants did not survive the trip.
Prevent curing knats
I use grit or sand in top of pot which seems to help. Then letting it dry out from the top and water from below. I like the sticky cards idea
Fungus gnats in houseplants
While in college (MANY years ago) I was too broke to afford potting soil for my split leaf philodendron so used outdoor dirt. OOPS. Fungus gnats worked hard to eat the roots and take over my dorm room. In desperation I put the plant into a large plastic trash bag and sprayed regular aerosol Lysol (from the cleaning closet!) on the dirt, then pulled up the bag around and over the plant. I gave it another heavy spray onto the bag walls and finished very tightly closing the bag. I left it sealed for a couple days, to live or die. Upon opening it, I found a living, if still stressed plant, and a thick layer of larvae. I scooped off the nasty baby bug layer then gave my green pet a good drink. SUCCESS!!! I make no guarantees how it might work on more tender plants, but it worked on the philodendron!
fungus gnats
I have powdered the soil as well as the saucers and trays upon which the containers sit, with diatomaceous earth. I also removed older plants from my greenhouse and repotted them with fresh soil with a smidge of d-earth. I then placed domes on the plants in trays to isolate the critters. What was an out of control greenhouse pandemic became a manageable small infestation quickly, easily handled with a spray bottle of 70% isopropyl alcohol. I knocked them out of the air when they took flight upon removing the dome.
Stinkers love bottom soil as well
Thank you! Everyone usually talk about how fn lay their eggs in the top two inches of soil, but no one really talks about them laying their eggs in the bottom of the pot as well, which is a problem im currently having. I have added a layer of sand and rock to the top of my potted plants and cut down on watering but to my suprise they seem to have just migrated to the bottom of the pot, thanks for the tips!
fungus gnats
Beneficial nematodes work great for eliminating fungus gnats. Had an an out of control infestation in my greenhouse, and after just two weeks of applying the nematodes, they were gone.
Hydrogen peroxide
I read on a forum, and then had success with, that using a solution of 1:4 hydrogen peroxide to water and watering the effected plant helps get rid of fungus gnats when used with other methods. It provides oxygen which kills the food source and the fizzy actions causes them to take flight and get stuck on those sticky traps. I usually treat potting soil with this before using because the bags in the garden center yard are exposed to all kinds of critters before being purchased. Don’t get carried away using this because too strong of a solution will harm plants.
fungus gnats
Can you not spray neem oil on the dirt and it kill these? I've used this in the past with houseplants that I normally set on my back porch during the warmer weather and I seem to recall it working well? I have not brought my plants in this year yet but will be doing so in the next week.
FUNGUS GNATS
A layer of playbox sand on top of the potting soil works every time for me. It is abrasive to the flies coming and going
Fungus Gnats
I read somewhere that cinnamon sprinkled on the soil worked. I tried liberally covering the soil around my peace lilies with cinnamon powder after a good watering. Following this, I then let the top dry out well and the gnats are gone. Plants are still healthy :)
Fungus Gnats
Either bake (solarize), or pour boiling water through any potting (at least the inert kind that contains no living compost in it's list of ingredients) mix that you intend to bring indoors. Also, buying potting mix well ahead of time and letting it sit in it's sealed bags for months before use, is often enough to disrupt the cycle. Most commercial potting mixes that contain active compost, will likely have fungus gnats.
Fungus Gnats
I'd like to ask a question regarding fungus gnats. It is often said that you should remove the top inch of soil regularly to remove eggs etc, so does this mean the adult gnats are capable of actually burrowing right down under the soil (up to an inch) to lay their eggs? The adults look so fragile you wouldn't think they would be able to burrow that far down.....
Fungus Gnats in Soil
Are there any suggestions for Fungus Gnats that are in the lawn? I live near a creek and the ground never gets super dry. Would beneficial nematodes help?
Thanks!
What concentration of hydrogen peroxide?
Having read all the positive comments regarding watering with a mixture of hydrogen peroxide and water, I thought I would try it to solve our gnats problem; but what percentage of peroxide is safe for this? I've seen various for sale from 3% all the way up to 90%?
I obviously don't want to use anything that will be toxic to either myself or my plants?
Thank you
Hydrogen Peroxide
The typical “drugstore variety” 3% peroxide is enough for dealing with gnats. We wouldn’t recommend anything higher than that for this purpose.
Rooting cuttings in water
You can't attract fungus gnats to cuttings rooting in water can you? Also where would I go to get verification of the answer.
Cuttings in Water
Fungus gnat larvae live in soil, so cuttings rooting in water will not attract them. A curious gnat may stop by to check out the cutting, but it will have nowhere to lay eggs and for the larvae to live.
Preventative Care
Hello, if two of my thrift indoor plants have fungus gnats, should I treat them all in case? Thank you.
Gnat eggs and larvae in outdoor pots
I'm looking for a solution for gnats in outdoor pots. At our Northeaster Wisconsin cottage we have many outdoor pots that stay outside all winter. In spring (Memorial weekend) my sister plants the pots up and we are immediately inundated with what we think are some sort of biting gnats, could be no-see-ems, but they are not mosquitos. They bite at the back of your neck at hairline or on scalp. These bugs seem to love us. It seems disturbing the soil is what sets them off. Does anyone have a protocol we can follow?
Gnats
They’re not black flies, are they? Fungus gnats do not bite.
In any case, you could try watering the containers (starting a couple weeks prior to Memorial Day weekend) using water that has been treated with mosquito dunks. This may kill the larvae of the flies, if they are in fact living in the container soil.
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