Fungus gnats are pesky little bugs that can live in the soil of your houseplants.
If you have ever had a plant with fungus gnats, then you know how frustrating and annoying they can be.
These little bugs can fly around your head and make it impossible to enjoy your plants.
While annoying, fungus gnats are relatively easy to control, though eliminating them completely is much harder.
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What are Fungus Gnats?
Fungus gnats are small, dark-colored flies with long legs and wings.
They are very small with the adults being, at most, 1/8 of an inch long.
Fungus gnats are most often found in damp, poorly drained soils.
Fungus Gnats or Fruit Flies?
At first, it may be hard to know if you have a fungus gnat problem or a fruit fly problem.
Both look similar, though their behavior is different.
If most of the flies you see are around your houseplants, you probably have fungus gnats.
On the other hand, if most of them are in your kitchen, especially if near the fruit, they are probably fruit flies.
How do Fungus Gnats Get in Houseplants?
Fungus gnats are most often introduced into the home through new plants or potting soil.
Unfortunately, it doesn’t matter what potting soil you buy, any brand can have fungus gnats.
I have gotten fungus gnats multiple times from the potting soil I have bought.
I’ve tried multiple brands and all have given me fungus gnats.
How Fast Do Fungus Gnat Populations Grow?
Fungus gnat populations grow very quickly.
Female fungus gnats can lay up to 200 eggs a day which can lead to a population explosion in just a few weeks.
It’s best to try to control the population early on before the second or third generation are laying eggs.
Are Fungus Gnats Harmful to Plants?
Typically fungus gnats are more annoying to you than harmful to your plants.
That said, if a fungus gnat infestation becomes extremely bad, it can eventually cause plant damage.
Fungus gnat larvae feed on decaying organic matter and fungi in the soil, which will not hurt your plant.
But, if you get large numbers of larvae they could start feeding on plant roots, which will hurt your plant.
Are Fungus Gnats Harmful to People?
Fungus gnats are not harmful to people or animals, but they are a nuisance.
Adult fungus gnats are attracted to light and tend to fly around people’s heads or into their drinks.
This can be annoying, but fortunately, the fungus gnats do not bite or sting.
How to Get Rid of Fungus Gnats
There are several methods for getting rid of fungus gnats, some easier than others.
Hydrogen Peroxide
One way to get rid of fungus gnats is to use hydrogen peroxide.
To do this, mix one part hydrogen peroxide with four parts water.
Then water your plants with the hydrogen peroxide solution.
Make sure you get the soil thoroughly wet and allow the excess water to drain out of the plant.
The hydrogen peroxide will kill the eggs and larval stage and eggs of the fungus gnat.
While this method does work there are a couple of issues with it.
Wet Soil
The first issue is that the soil ends up very wet, which can cause problems on its own.
Some plants will get more stressed by wet soil than they were from the fungus gnats.
Kills the Beneficial Bacteria
The second problem is that hydrogen peroxide can kill the beneficial bacteria in the soil.
Killing the beneficial bacteria in your soil means your plants may not get the nutrients they need.
Let the Soil Dry Out
One of the best ways to get rid of fungus gnats is to let the soil of your indoor plants dry out.
This works because fungus gnats need moist soil to lay their eggs and for the larvae to survive.
Without eggs or larvae, the fungus gnat population will die off.
Fungus gnat eggs and larvae can live for a day or two in dry soil, so if your plants can tolerate it, wait at least 3 days after the soil dries to water next.
Adult gnats can live about a week, meaning they may lay more eggs once you water again.
But if you consistently let the top two or three inches of soil dry out between waterings, you will have significantly fewer fungus gnats.
Also, make sure all the pots you use have drainage holes to prevent the soil from staying too wet too long.
Repot the Plant
Another way to get rid of fungus gnats is to repot the plant.
When you repot the plant, you want to make sure you use new potting soil.
If you use old potting mix, there is a chance you will end up with fungus gnats again.
You also want to make sure you are using a clean pot or clean the current pot before putting the new soil back into it.
Unfortunately, there is still a risk that you will end up with fungus gnats again, as any potting soil, new or old, can have fungus gnat eggs in it.
Yellow Sticky Traps
Yellow sticky traps are my favorite method of getting rid of fungus gnats.
Just be aware that if you have cats like mine, they will occasionally be racing around the house with a yellow sticky trap stuck to them.
My cats seem to think these things are awesome to chew on and have been known to get them stuck to their tails or belly.
Yellow sticky traps work by attracting fungus gnat adults to them and then they get stuck to the trap.
These are super easy to use, just peel the paper off both sides and put the nonsticky part into the soil near the plant.
When I’ve used these, I’ve had fungus gnats land on them within a few minutes.
The yellow sticky traps I bought on Amazon say they are good for two to three months or until more than half the trap is covered in bugs or dust.
You can also buy them at some garden centers.
Cinnamon
Cinnamon, sprinkled on the soil surface, is another method that may work to get rid of fungus gnats.
Cinnamon is a natural fungicide and helps to control fungus gnats by destroying the fungus the larvae feed on.
To use this method you need to sprinkle enough on top of the soil to get a visible layer and repeat every couple of weeks.
You will also want to bottom water during this time, otherwise, the cinnamon may get nasty and moldy.
Apple Cider Vinegar Traps
You can also make a trap using apple cider vinegar and dish soap in a deep bowl or jar.
To do this just pour apple cider vinegar into your container until it is about a quarter to half-inch deep.
Then add a few drops of dish soap and stir it.
Cover with plastic wrap or clear tape, leaving a small opening.
Alternatively, you can just poke some holes in the plastic wrap with a toothpick.
Make the holes big enough for the fungus gnats to go through, but not so big that they can fly back out.
Finally, place it near your plant.
The gnats will be attracted to the smell and will fall in.
Once they fall in, they won’t be able to get back out and will drown.
Change the solution every few days or when it gets full of gnats.
This method also works on fruit flies, just place it near where you see the most fruit flies and it should help.
Neem Oil Soil Drench
If you want to use a more natural product, you can use neem oil.
Neem oil is a natural insecticide and will help to get rid of fungus gnats.
To use this method, you need to make a neem oil soil drench.
To do this, mix one tablespoon of Neem oil and one teaspoon of dish soap (or castile soap) with one quart of warm water.
Make sure to mix well and use right away.
Neem oil starts to break down once it’s mixed with water, so only mix up what you will use.
Raw Potato
Cutting up a raw potato and placing it cut side down is supposed to draw the larvae up and into the potato, removing them from the soil.
Toss and replace the potato every few days until you don’t see evidence of larvae on the potato or the adult population has decreased.
I have not personally tried this method as I’m fairly certain my dogs and cats would not leave the potato alone and would most likely knock the plant down in the process of trying to get it.
Mosquito Bits
Mosquito bits are small pellets that you can sprinkle on top of the soil to help get rid of fungus gnats.
The active ingredient in mosquito bits is Bti, which is a bacteria that is deadly to fungus gnats (and mosquitos) but harmless to other living creatures.
The Bti will kill the larvae and help to control the population of fungus gnats.
If you don’t want to sprinkle the bits on the soil, they can also be soaked in the water you plan to use for watering your plants.
To do this take a quarter cup of mosquito bits and mix them into 1 gallon of water.
After 30 minutes or so, scoop the bits out and use the water within 2 days.
Repeat weekly for 3 weeks.
Make sure to stir the water before using it to ensure it is mixed evenly.
If you don’t want to deal with the mess of scooping the bits out after soaking, place them into a fine mesh bag or nylon stocking before soaking them.
You can find mosquito bits at most garden stores or buy them here.
Use Insecticides
For severe infestations, you can use an insecticide.
Most home insecticides will kill the adults, but they may or may not help with the eggs and larvae.
Make sure to read the label and follow the label directions closely.
If you have pets or small children that may play with your houseplants, other methods are better options for fungus gnats.
How to Stop Fungus Gnats from Spreading to Other Houseplants
If you find fungus gnats in one houseplant you will want to do what you can to prevent them from spreading to more plants.
Fungus gnats are weak fliers and tend to stay close to their home plant.
Use this to your advantage and separate the infected plant from other house plants.
You will also want to be extra vigilant in checking your other plants for fungus gnats.
Be sure to check the soil and leaves for any bugs or larvae.
How to Prevent Fungus Gnats
The best way to get rid of fungus gnats is to prevent them from infesting your plants in the first place.
Don’t overwater
The number one best way to prevent fungus gnats is to not overwater.
Fungus gnats love damp soil and will lay their eggs in it.
Allow the top inch or so of soil to dry out between waterings.
This will help prevent fungus gnats from infesting the soil.
Water Plants from the Bottom
Another way to help prevent overwatering (and, in turn, fungus gnats) is to water your plants from the bottom.
To do this, place your plant in a sink or shallow bowl of water and allow the water to soak up from the bottom.
This will help to evenly moisten the soil without overdoing it.
It also prevents the top of the soil from getting too wet.
Fungus gnats could still get into the plant through the drainage hole, but it’s a much smaller opening for them.
Use Soil Covers
If you live in a humid climate or tend to overwater your plants, you may want to consider using a soil cover.
A soil cover will prevent the fungus gnats from getting to the soil to lay their eggs.
No eggs in the soil mean no larvae to worry about.
There are a few different types of soil covers you can use.
One is to simply place a layer of gravel or sand on top of the soil.
This will block the fungus gnats from getting to the soil while still allowing water and air to reach the roots.
Another option is to use insect-proof netting.
This will also block the fungus gnats from getting to the soil while still allowing water and air to reach the roots.
Either of these options will help to prevent fungus gnats from infesting your plants.
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