Get rid of fungus gnats now! Personally, I have tried every other method recommended but with no success. See how I get rid of fungus gnats effectively and safely!
How to get rid of fungus gnats is easy, and natural but ongoing. I tell you why you are never free of these plant gnats and I have links to what I use. Learn how to kill not only the fungus gnats but also the fungus gnat larvae.
I wrote this article as I was getting so many questions on how to get rid of gnats in houseplants aka indoor plants. Be sure to read to the end as I added some updated information for you.
What Are Fungus Gnats – Plant Gnats?
Fungus gnats (families Mycetophilidae and Sciaridae) are the grayish-black, delicate little winged critters that resemble fruit flies or tiny mosquitoes. They love humid and moist conditions.
If you have bugs in your soil that fly up from your houseplants when watering then you most likely have fungus gnats!
Are Fungus Gnats Harmful?
Yes! The adults can cause harm to your plants by spreading fungal diseases to your plants and seedlings. Worse yet, they lay eggs, a lot of eggs in the soil.
A typical fungus gnat can lay up to 300 eggs.
When the fungus gnat eggs hatch the gnat larvae in the soil feast on the roots of seedlings, young plants, and cuttings you are attempting to root.
This can weaken and kill your plants.
Can you see why we need to control these houseplant pests?
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Why Fungus Gnats Persist
Fungus gnats persist because new plants you bring home and potting soils all have them.
These insects live and breed in the soil. That is why you can’t get rid of fungus gnats once and for all.
Gardeners can’t get away from it. It is part of the great circle of life, especially if you are an organic gardener.
Potting soils purchased at garden centers, big box stores, and so on are all stored together.
The potting soils are moist and full of conditions fungus gnats love to breed in.
It is no one’s fault.
If you have a fungus gnat problem it is not because you are overwatering. I roll my eyes each time I read someone saying that.
Case in point, I was rid of the fungus gnats in my home. I suddenly noticed I had them again and wondered what was going on.
I water on a consistent schedule and adjust as the needs of plants change because of the environment and season.
Then I remembered I had brought home some herb plants that were on sale at a great price at a big box store and had placed them on my kitchen window sill until I could get them re-potted and into the greenhouse to grow on.
Sure enough, the plant soils were infested with fungus gnats.
Hydrogen Peroxide and Fungus Gnat Larvae
Many gardeners I know love to use Hydrogen peroxide to kill fungus gnat larvae.
I cannot claim that it is strictly organic as the 3% solution you can purchase has chemicals and additives in it that may not fit the criteria.
To use 3% hydrogen peroxide first dilute it to a mix of 4 to 1. An example of that is 1/4 cup of the 3% peroxide to 1 cup of water.
You can water with the diluted hydrogen peroxide solution from the top of the soil if you don’t splash the leaves.
If it is seedlings and you can’t water from the top then you can set the seedling pots or tray into the solution to soak up from the bottom. (I have found that seedlings are super tender and you may need to dilute it more or use an alternate method)
I have had limited success with hydrogen peroxide so if you find that it does not do the trick for you either, read on.
Treat Fungus Gnats at Home
One of the best fungus gnat killers is Yellow Sticky Traps. Yep, these simple little yellow pieces of sticky paper.
They keep the population of adults down so they cannot lay eggs and repeat the circle of fungus gnat life.
When the flies in your plants start to come out when you water and fly up they land on these traps to their everlasting demise.
They come with little wire spikes to stick them into the soil but I don’t use those. I peel one side of the paper off to reveal the sticky stuff.
Then lay it, sticky side up, on an edge of the pot that I have noticed gnats swarming up from when watering.
On my plants inside the house, I see an outbreak typically at the end of February and the beginning of March so I set out traps.
After a few days, I see them starting to pile up on the traps.
To control fungus gnats inside my greenhouse I keep sticky traps out all year round.
My greenhouse is where I re-pot plants, start seeds, etc and I have my bags of potting soil or mix my own from my compost so fungus gnats get brought in constantly.
(I don’t like the odor of Neem drench so I don’t use it in my greenhouse either)
It sounds too simple but that really has been the easiest and most effective method to control fungus gnats.
I purchase my sticky traps at a local garden center. They can also be bought from Amazon and box stores.
Not only do they work for Fungus Gnats but also White Fly, Aphids, and Leaf Miners. More bang for the buck!
Some people make their own but the traps are so inexpensive that it is not worth the bother to me.
Some have mentioned that the traps can catch beneficial insects too but I have not had that be an issue. Mostly I only catch the fungus gnats and recently a spider.
Be gone you pesky gnats!
Mosquito Bits for Fungus Gnats
This is an update to this article. I found out about this a couple of years ago and it works!
When you use the yellow sticky traps and the bits together you have a well-rounded method to get rid of both the adults and the larvae.
Mix the bits into any new potting soil you use and you should see a dramatic reduction in any fungus gnats problem.
This year I have been putting the Mosquito Bits granules into the pitcher of water I let sit out to come to room temperature before watering.
This allows the agent that kills the larvae to filter through the soil of established plants.
I had been sprinkling it on top of the soil but then I noted the granules would grow mold.
Is your Potting Soil Infested?
Crazy as it sounds sometimes I pasteurize my soil if I notice an excess of fungus gnats before potting up sensitive plants and cuttings. Do I always do this?
No, but it has been effective for so many problems.
Buying sterile seed starting mix takes care of the need to pasteurize but I was starting seeds on a larger scale and wanted to use my own compost mix.
Not only does pasteurizing get rid of the larvae present in just about any potting soil out there but it will also get rid of the pesky bacteria that can cause damping-off when you start seeds.
This temp is enough to get rid of the bad organisms without killing the good.
How to Pasteurize Soil
Note: I no longer bother with pasteurizing when just repotting plants, I tell you why at the end of this article.
Pre-heat your oven to 200 degrees Fahrenheit. Pour up to 4 inches of your potting soil into a large baking pan (I like the large aluminum ones you can get at the Dollar Store) and put a meat thermometer in the center of the tray, deep into the dirt.
Place the tray in the oven and keep an eye on the dirt’s temperature. Once the center of the dirt reads 160 degrees, bake for 30 minutes.
Allow the dirt to cool thoroughly before using.
When I am in a hurry, I pour boiling water through the soil, in a wire sieve and let that do the work. (I primarily do this now as it is so easy to do though a bit messy so it is an outdoor job)
What hasn’t worked to get rid of fungus gnats
When researching how to handle fungus gnats I came across many methods that sounded good but did not work for me when I tried them. (others may have found them effective, but I did not)
Letting the soil dry out.
This did not work because a few of my plants got stressed and showed signs of it by getting brown leaf tips like my Peace Lily (Spathiphyllum) Peace Lilies like constant moisture.
Also, new cuttings just rooted and planted need to be kept moist to grow best so letting them dry out to the first two inches would be a death sentence for them.
We are talking moist, not drenched but they do need constant moistness to thrive.
And that is doubly so for seedlings, letting them dry out is a huge no-no.
Removing topsoil and replacing it with sand.
If you get potting soil that is already infested then the bug larvae are deep enough to be noshing away on the plant roots.
Sand is supposed to discourage the adults from laying eggs and continuing the cycle but if you read above on why fungus gnats persist you will see why this is just added work.
I did try it though but did not get the results I wanted. The rascals started to go in along the bottom drain hole instead of on top.
There are a couple of things I have not tried which are an organic pesticide soil drench (Neem, I have it but don’t use it for plants in my home as I don’t care for the odor of it) or beneficial nematodes.
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