Fungus gnats are tiny, annoying insects that you’ve likely seen flying around your houseplants at one point or another. They don’t actually bite or harm humans in any way, but your plants are a different story.
Fungus gnats and their larvae can go from a minor nuisance to a major infestation very quickly. This is because adult females can lay up to 300 eggs in the soil of your plants in only one week!
Fortunately, there are several simple solutions to getting rid of these persistent pests. Read on to learn about how to get rid of fungus gnats in houseplants easily and organically.
What Are Fungus Gnats?
Fungus gnats are sometimes mistaken for fruit flies because they look very similar. They are tiny flies with a mosquito-like appearance when looked at through a magnifier. Adults are typically only about ⅛” in length.
In their natural outdoor habitat, the gnats live in rich and moist soils and feed on fungi, plant roots, and other types of organic material.
Unlike fruit flies, which are drawn to ripening fruit and other unrefrigerated produce, fungus gnats look for damp soil to live on and lay their eggs in. You’ll typically only see them in your house around indoor plants because they don’t like flying long distances.
Houseplants provide oxygen and brighten up your home, but they can also attract fungus gnats, which are annoying and may damage your plants.
Once they become adults, fungus gnats only live for about a week, but that’s enough time for the females to lay hundreds of eggs.
The eggs will hatch into larvae that look like tiny (¼”) maggots with white bodies and black heads. It can be difficult to spot the larvae because they are so tiny and spend most of their time just under the surface of the soil.
After a little over two weeks, the larvae have become young adults and leave the soil to start the cycle all over again.
How Fungus Gnats Do Damage
Adult fungus gnats are a nuisance but aren’t actually harmful to your plants or to humans. They don’t bite and can’t transmit any kind of disease to people.
Larval fungus gnats, however, can do a lot of damage, especially if your plants get infested. Until the larvae become adults, most of what they do is eat. They feed on fungi and organic material in the potting soil but will also feed on the roots of your houseplants.
A few larvae won’t do enough damage to actually hurt your plants, but they can be trouble for young or sensitive houseplants. And if the larvae population gets out of control, they can do damage even to full-grown houseplants.
Besides potted plants, fungus gnats are especially a problem for seedlings. If you start any kind of seeds indoors in the spring, you definitely need a plan to control fungus gnat larvae.
Fungus gnats are similar in appearance to fruit flies, but they have grayish bodies instead of reddish-brown. They are also attracted to damp soil rather than fruit.
The seedlings have small root systems that the larvae can easily eat through. Fungus gnats can also transmit the plant pathogen that causes damping off, which is one of the most common seedling killers.
Identifying a Problem
Having a few occasional fungus gnats is not a problem, but how do you spot an infestation that could damage your plants?
First, regularly check around your houseplants for the adult fungus gnats. If you notice that there are more and more of them, they are probably turning into a serious problem.
Next, you can check the soil in your potted plants to see if you can spot the larvae. Sometimes they will be on the surface, but you may need to gently move the soil around a little bit to check beneath it.
You’re looking for very small, maggot-like larvae.
If you can’t spot any larvae but still suspect their presence, there’s a simple test you can perform. Cut out a small wedge of raw potato and lay in on the surface of the soil around your houseplants. You can do this for each houseplant you have.
The larvae will be drawn to the raw potato and start feeding on the bottom of it. Leave it there for a few hours or overnight, then turn over the potato wedge to look at the underside. If you see a bunch of tiny maggots on the potato, you have a fungus gnat problem.
Using a raw potato wedge is an easy way to see if your potting soil has fungus gnat larvae. Just leave the wedge on overnight and flip it over to see if larvae are feeding on it.
Finally, you can also look at the houseplants themselves to identify a harmful infestation.
Larvae harm the roots of your plant, so look for symptoms related to root damage. If you notice leaves that wilt suddenly, start turning yellow, or start dropping off the plant for no apparent reason, it could be fungus gnat larvae.
Benefits of Natural and Organic Control
There are insecticides you can use to control fungus gnats, but it’s best to always opt for natural methods if at all possible.
Insecticides and other pesticides often have strong chemicals that can be harmful to your health and may kill beneficial organisms in the soil. If you have pets, they may end up breathing in the insecticide, which can cause an allergic reaction or other problems.
With fungus gnats, you don’t need strong chemicals to get rid of them.
Many of the following solutions use everyday ingredients that you likely have in your pantry. Others are inexpensive solutions that won’t harm you, your pets, or your houseplants.
How to Get Rid of Fungus Gnats in Houseplants
These solutions are for an existing infestation or if you notice that the population of fungus gnats keeps growing.
If you want to learn how to prevent fungus gnats from being a problem in the first place, be sure to read the section after this one for simple, natural prevention methods.
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All you need for this method is some apple cider vinegar, dish soap, and a shallow container or cup.
Fill your small container about halfway full with vinegar and mix in a few drops of dish soap. Normally, gnats and fruit flies can stand on liquid, but the dish soap disturbs the surface tension, so they’ll end up sinking instead.
Place your container or cup of vinegar and dish soap near your houseplants. If you can fit it, put the container right on the soil in one of your pots. (Remember, fungus gnats don’t fly very far.)
Leave it there for a few days and check to see if the fungus gnats are attracted to the vinegar. You’ll know it’s working when you see dead gnats at the bottom of the container.
This method is simple but has a varying success rate. Fungus gnats aren’t as attracted to vinegar as fruit flies are. If they don’t seem to be going for the vinegar, move on to one of the next methods.
Yellow Sticky Traps
Yellow sticky traps are one of the easiest and most effective ways to control adult fungus gnats.
The yellow color is designed to attract several different pests including fungus gnats, whiteflies, and aphids. The sticky surface of the trap will glue the gnats in place, effectively killing them.
This method is very effective because it will drastically reduce the population of egg-laying adults. If there are already larvae in the soil, you may need to get rid of those as well, but the important part is to disrupt the cycle of the fungus gnats.
Yellow sticky traps are one of the most effective ways to control fungus gnats, but they don’t usually look aesthetically pleasing. To fit in better with your decor, try buying the decoratively shaped traps.
The sticky traps are often sold as rectangles that you can cut into smaller squares and place horizontally on the soil around your houseplants.
You can also try a specific yellow sticky trap called Gnat Stix that is designed to be attached to a small wooden stick that can be stuck down into the soil.
The only real downside to the sticky traps (apart from accidentally getting them stuck to your fingers) is that they don’t look very attractive. If you don’t like the idea of yellow strips cluttering up your houseplants, try these sticky traps shaped like butterflies and flowers.
The most important part of this method is to leave the traps out for at least a month. The life cycle of a fungus gnat from egg to adult typically runs 3-4 weeks. New eggs will keep hatching until you get the adult population under control, so keep the traps going for at least this long.
To test if the fungus gnats are gone, just put out a small square of clean sticky sheet. If you don’t see any gnats on it after a few days, that’s a sign you can remove the traps.
Hydrogen Peroxide Solution
If you know that larvae are present in the soil around your houseplants, using diluted hydrogen peroxide can get rid of them.
Start with hydrogen peroxide 3% (which is the standard solution sold) and mix one part of the peroxide with four parts of water. Water your houseplants with this solution, making sure that it sinks down into the top few inches of soil.
A diluted solution of hydrogen peroxide can kill gnat larvae and will go on to break down in the soil without harming your plants.
The hydrogen peroxide should kill the gnat larvae and will go on to break down in the soil. As long as you dilute it with water, there will be no harm to your plants.
To be sure it’s worked, use the hydrogen peroxide solution a second time, waiting until the top few inches of soil dry out first. You can also use the raw potato wedge test to see if any larvae are left before using the solution again.
As a last resort, you can also turn to a natural insecticide. Natural pesticides don’t have the same harsh chemicals that traditional ones do, but they should still only be used if other methods have failed or if you have a very severe infestation.
For fungus gnat larvae, you can try an insecticide known as AzaMax. Its main active ingredient is azadirachtin, which is naturally derived from neem trees.
Neem-based products are often used in organic farming and gardening because they are effective and plant-based. AzaMax is OMRI listed, which means it’s approved for use in organic farming and something you can feel comfortable using in your home.
To use, follow the instructions on the bottle for correctly diluting the AzaMax with water. Then, water your plants with the solution you made, making sure the top few inches of soil get wet.
Unlike conventional insecticides with harsh chemicals, a natural one like AzaMax can fix a fungus gnat problem without harming plants or people.
AzaMax will kill both larvae and eggs and is a quick fix for a fungus gnat problem.
The best way to control a fungus gnat infestation is to prevent it. With just a few simple tricks, you can avoid being overrun by gnats altogether and save yourself time and effort.
Let the Potting Soil Dry Out
Fungus gnats are attracted to damp soil because it provides a good environment for their eggs to hatch. The larvae also prefer a damp habitat and feed on the mold and fungi that grow in wet conditions.
To discourage fungus gnats, let the top 1-3” of soil dry out in between waterings. (Just don’t let the whole pot dry out because this will kill your houseplants.)
Remember that your plants have a root system that usually goes almost to the bottom of the pot they are in. They will be fine if the top few inches dry out, and the gnats will look elsewhere for a home.
In fact, most houseplants don’t like being wet all the time. Letting them dry out in between waterings will help your plants be healthier as well.
Good watering habits can prevent fungus gnats from becoming a problem. Let the top few inches of soil dry out every time before you water your houseplants.
If you already have larvae present in the soil, you can also let the soil dry out to kill some of them and keep some of the eggs from hatching.
This method won’t completely prevent fungus gnats from appearing, but it will definitely keep them at a low level so that they can’t harm your plants.
Isolate Infected Plants
If one of your houseplants ends up with a fungus gnat infestation, move it to a different room without any other plants.
Because fungus gnats typically only fly short distances, this will help stop them from spreading to your other houseplants. If the infested plant was already close to other plants, keep an eye on them for signs of larvae and gnats.
Isolating affected plants as quickly as possible is your best bet for keeping the infestation contained.
Mosquito Bits are what’s known as a biological control. They contain a specific species of bacteria called Bacillus thuringiensis.
Bacillus thuringiensis are microbes naturally present in certain soils that selectively target and kill the larvae of several pests without harming beneficial insects or humans. They are frequently used in organic growing methods and to naturally control mosquitoes.
In spite of the name, Mosquito Bits will effectively kill fungus gnat larvae. You can sprinkle the bits on the soil surface of your potted plants or mix it in with the soil when potting new plants.
Adding a biological insecticide like Mosquito Bits to the soil around your houseplants can both prevent fungus gnats from hatching and control an existing infestation.
Because bacteria won’t survive indefinitely without something to feed on, the Mosquito Bits will not be effective long-term.
You can either reapply them at certain intervals or use something longer lasting like Mosquito Dunks.
Can I Avoid Fungus Gnats Altogether?
Unfortunately, the only way to avoid fungus gnats altogether is to keep your house free of potting soil (which means no houseplants).
The eggs of fungus gnats are usually already present in the potting mix you buy from the store. When you pot and water your plants, the moisture causes the eggs to hatch.
If you consistently let the top part of the soil dry out in between waterings, you should only ever see a few fungus gnats flying around, and they will eventually die out. This is probably the best method out of all of these for preventing any problems!