How to Get Rid of Fungus Gnats in Houseplants

Last Updated on October 31, 2021 by Phil

Hate fungus gnats and fungus gnat larvae? Here’s how to get rid of fungus gnats in houseplants.

These plant pests rank among the most annoying and frustrating around. They grow in number quickly and can wreak havoc to your plants where you can’t see it.

Thus, by the time you see the damage being done they’ve already turned into an infestation.

The good news is, if you know what to look for and how to treat them, you can rid your house plants from fungus gnats and their larvae once and for all.

Here’s everything you need to know to do that.

Table of Contents

What Is a Fungus Gnat?

Fungus gnats look very much like mosquitoes but are often confused for fruit flies. They are small, pesky and bothersome. But, the biggest difference between the two is that mosquitoes prey on people while fungus gnats attack plants.

These plant pests are small, reaching about a quarter of an inch long, often less. And, they have wings so they can fly. But, they tend to spend most of their time on the soil of houseplants and only fly once in while.

Yes, fungus gnats love house plants. And, they are prevalent in indoors plants because of the excess moisture. This is less of a problem outdoors because there’s more exposure to sunlight and wind. Thus, soil tends to dry faster there.

It is also important to note that while fungus gnats are not attracted nor are they harmful to humans. They do not spread disease, bite or sting. They can be annoying though.

Instead, they pose a huge problem for plants because they can cause serious damage as their population grows.

Interestingly, it isn’t the adult fungus gnats that do the damage. Instead, it is the younger larvae. These eat not only fungi in the soil but also the roots of your plants.

And, unlike other pests, they don’t take a break. That’s because winter does not faze them. Nor do they hibernate. So, they’re active all year round.

How To Identify Fungus Gnats

Fungus gnats are a bit tricky because you’re not just looking for one particular insect. Instead, they present themselves in many forms.

To better understand the fungus gnat, and how to identify it, it helps to understand its life cycle.

Fungus Gnat Life Cycle

Let’s begin with the adult fungus gnat:

Adult gnats lay eggs. They can lay up to 200 eggs on the soil. They typically look for areas with organic matter which is what the young gnats will feed on. It takes about 8 to 10 days for this to happen.
After 4 to 6 days, the eggs hatch into larvae.
Larvae look like very tiny, transparent, or translucent colored worms. These larvae then burrow into the soil to look for food. Food comes in the form of organic material and fungus.
In about 2 weeks, the larvae turn into pupa, and stay in that form for about 4 to 6 days.
Finally, adult gnats emerge from the soil. Adult gnats live for a week or more with the purpose of laying eggs.
And, the process repeats itself.

Because the fungus gnat’s life cycle is very short, you’ll see many generations overlap with one another. At the same time many of them will be born one after another.

This makes them able to grow fairly quickly.

Identifying Adult Fungus Gnats

As mentioned, fungus gnats look like mosquitoes or fruit flies. But, they’re quite different from the latter in that they have slimmer torsos and have longer, thinner legs as well.

They also don’t spend a lot of time flying around. Since they lay eggs on the soil, they like to stay around the surface of the soil and around the pot.

The reason I went through fungus gnat’s life cycles is to illustrate that they only spend a short time of their lives as adults.

The rest of the time, they are eggs and larvae. As such, you want to be watch out for both these forms as well.

Identifying Larvae

Fungus gnat larvae look like tiny transparent colored worms. Because they’re small, they look like specks on white on soil.

Just as importantly, once you see adult gnats around, there’s almost a 100% chance that there are eggs and larvae somewhere near as well.

Larvae can’t fly because they haven’t developed wings. As such, they stay on the soil. Typically, they’ll be near organic matter and fungi.

But, as they grow in number, the larvae will also turn their attention to the plant’s roots, which will cause more problems.

Signs of Fungus Gnat Larvae and Adult Fungus Gnats

Besides looking for the fungus gnats themselves, knowing the signs of the damages they cause can also help you make a diagnosis.

Unfortunately, many of the signs are very similar to other pests. This can make it difficult to identify which pest is present, and thus, affecting the kind of treatment to take.

That said, signs of fungus gnats and their larvae include:

Wilting plants
Leaves turning yellow
Leaves dropping
Slow growth
No growth

Since the larvae are doing the damage and they will be targeting the roots of the plant, the symptoms are similar to other root problems.

Why Are Fungus Gnats Bad?

A small number of fungus gnats seldom causes any problems. They become more of a nuisance. Unfortunately, from above, you know that this will never last long because adult gnats lay so many eggs.

That’s when bad things happen to your houseplants.

As the number of fungus gnats grows, so too the eggs they lay. This in turn causes lots of larvae to be born.

More importantly, it is the larvae that actually causes the problems not the adult gnats. That said, you also need to get rid of adult fungus gnats because they’re the ones laying the eggs.

Fungus gnat larvae are the ones that feed. They will feed on organic matter in soil as well as fungi. But, as their population grows, they will start feeding on the roots of the plants.

Since the root tips are what absorbs nutrients and moisture form the soil, damaging these will eventually prevent the plant from getting enough sustenance from the soil.

As such, you’ll see yellow leaves, dropping leaves and a wilting plant. Left untreated, the house plant eventually dies.

Fungus gnat larvae are particularly attracted to seedlings. Because, young plants have few roots that are still delicate, they easily succumb to these pests.

Besides the damaging roots, fungus gnats also tend to spread diseases which harms the plant.

When Do Fungus Gnats Come From?

Fungus gnats tend to come from:

Plants you just took home from the nursery or from friends
Infected potting mix
Plants you left outside for the summer and bring back indoors
Open windows

In general, fungus gnats thrive in moist conditions. They will seek out moist environments which means that houseplants that are overwatered or waterlogged are their most likely targets.

In the wild, you’ll find them in regions of the forest that are damp.

They particularly like houseplants because many people tend to water their indoor plants too much. The warm temperature is also something they enjoy. This makes them prevalent in greenhouses. Although, they are not deterred by the cold which is why they’ll still be active during the winter.

In fact, you’ll likely notice fungus gnats more in the fall and winter despite them being very active in the spring and summer.

This is especially true if you leave the plants outside during summer. Therefore, they stay out of sight for the most pat. But, the moment you bring them in, you’ll quickly notice their population increase due to favorable conditions (warm, cozy, less sunlight, less air circulation, more water).

Similarly, the colder weather also means you’ll stay indoors more. Thus, it is easier to notice something happening with your plants.

In addition to the environment, fungus gnats need to feed to survive. This comes in the form of organic matter and fungi. Both of which either occur or develop in moist soil.

Other things that attract them include:

Bright light
Yellow color
Mold and mildew
Potting mix heavy in coco coir and peat moss
Soil that does not drain well

As mentioned, overwatered soil, damp and wet conditions are something they look for as well.

How to Get Rid of Fungus Gnats

Here are proven ways to get rid of fungus gnats on houseplants. You can use any of the methods depending on what you have at home and which you prefer.

Do note that the results can vary by plant since some plants may be more sensitive to certain kinds of ingredients.

Hydrogen Peroxide and Water

If you have hydrogen peroxide lying around at home, you can use it. But, before you do, make sure it is the regular 3%. You don’t want to use too much strength or concentration which is why we’ll be diluting it with water

The hydrogen peroxide and water solution is most effective for killing fungus gnat eggs and larvae. To make it, mix:

1 part of 3% hydrogen peroxide
4 parts water

You can put this in a spray container or pout on the soil. But, before you do, make sure that the soil is dry. You want the solution to saturate the soil so it can penetrate down a few inches deep. The deeper it can reach, the more effective it will be.

After that, water the plant. You’ll heard a chemical reaction in the form of fizzing and foaming. That’s to be expected so don’t worry.

Be careful not to overwater the plant.

After a while, the solution will break down in the soil. it is not harmful to plants so there won’t be problems after.

But, like the other treatments, it takes a few time for this to completely get rid of the eggs and larvae because they need to come into contact with them. So, you’ll need to repeat every so often.

Organic Fungus Gnat Control

In addition to the hydrogen water mix, there are a few other organic ways to get rid of fungus gnats in plants. I’ll group them together below.

Neem Oil

Neem oil is one of my favorite pest control solutions. That’s because it works on many different insects and bugs, including fungus gnats.

You can purchase concentrate neem oil which is inexpensive. This is the pure stuff. I tend to avoid the pre-mixed ones because they can include other additives and chemicals in there.

But, when using pure or concentrated neem oil make sure to dilute it with water before applying on plants. That’s because too much concentration will damage some plants. The manufacturers will have instructions.

You can use neem oil like the hydrogen peroxide mix, on the soil. I also like to create a spray and spray affected parts of the plant itself. This will get rid of adult fungus gnats.

But, since there needs to be contact between the spray and the pests, you’ll want to target areas where they tend to hide.

Repeat as needed until the fungus gnats are gone.

As a bonus, neem oil also works as a preventive measure which keeps pests away from plants.

Pyrethrin Spray

This is a less common solution. But it works as well.

You only need to spray a thin layer on both the soil and affected parts of the plant. Avoid getting either wet from too much spray.

AzaMax

Azamax is a botanical insecticide and miticide. So, it is designed to kill a few kinds of pests including fungus gnats.

Its main ingredient is azadirachtin which is the active ingredient in neem oil. The difference between the two is the neem is natural and organic. Azamax is a commercial products.

As such, AzaMax is a stronger concentration which makes it more effective, but it can also cause some problems with more sensitive plants. So, make sure to test on a small area of the plant and wait to see what happens the next 24 hours before trying on larger areas.

Cider-Vinegar Traps

In case you have apple cider vinegar at home, you can use likewise use that to create a cider-vinegar trap.

You’ll need a small, shallow container. And used tuna can works great.

Then mix.

1 part apply cider vinegar
1 part water
A few drops of liquid dish soap or mild liquid soap (to help mix/bind the vinegar and water)

You’ll need at least a depth of quarter of an inch of the mixture.

Stir the mixture.

Place the container on the soil in the pot.

Flypaper

This is going the old fashioned way. Originally designed to catch flies by making them stick to them should the fly land on the paper, it will do the same for any fungus gnat that lands there.

Yellow Sticky Card Traps

If you feel that flypaper is messy since it can stick to things including curious dogs (Yes, mine has and believe me, it’s a headache to remove from all the fur. Although, it was fun to watch her get irritated by it for a minute or so before I started to try and get it out), you can go with yellow sticky traps instead.

These are hung instead of laid out, so they’re less bothersome to a certain extend.

Anyways, fungus gnats are attracted to the color yellow. As such, they’ll find their way there and get stuck to the traps.

The downsides to these yellow sticky traps is that fungus gnats, unlike flies, don’t fly around nearly as much. Instead, they spend most of their time laying eggs or as larvae and eggs. So, the yellow traps are only partially helpful and will not completely eradicate your fungus gnat infestation.

Allow Potting Soil to Dry Out

Wet soil or soil that is consistently moist appeals to fungus gnats. This is why overwatered plants or waterlogging tends to cause these pests, among others to attack your plant.

Damp environments cause mold and algae. Both tend to attract fungus gnats. So, by limiting the moisture, you’ll also help get rid of these pests.

The simplest way is to allow the top 2 inches of the soil to dry out completely before you water again. In addition to reducing the risk of mold and algae it also prevents fungus gnat eggs from hatching.

Repot If Needed

In case the fungus gnat infestation is large or there are a lot of larvae on the soil, it may be a better option to just repot the plant.

It is best to do this outside and away from your garden. Staying somewhere there’s concrete or pavement, as long as you’re away from other plants, the lawn or soil helps. Then repot there.

Make sure to get rid of all the infested soil. You don’t want any bit of it to go to the new pot (you can reuse the same pot provided you make sure to sanitize and clean it thoroughly before reusing). You will also need to rinse the roots to get rid of the excess soil around the plant as well.

Apply Insecticide

While it may not be your first choice, insecticides are the most effective and fastest way to get rid of a fungus gnat problem. However, there always come the risk of toxic chemicals. So, do choose the product carefully.

If you have dogs or cats, you may want to be extra cautious about this. Or, move the plant somewhere your pets can’t get to it.

Since eggs and larvae reside on the soil while adults do spend some time on the plant, you may need to spray the plant as well. That said, fungus gnats often go towards the roots in the soil so you may just focus more on the soil rather than the plant. This reduces potential plant damage as well.

How To Stop Fungus Gnats Spreading To Other House Plants

Like many pests, fungus gnats will spread from one plant to many others if you leave them be. So, if you have many houseplants, you’ll notice all of them have been infected.

As such, it is very important to separate and isolate the affected plant as soon as you spot any fungus gnats or signs of potential infection. It is also important to check any nearby plants in case the pests have already started spreading.

Doing a quarantine and treating the infested plant is the only way to limit the problem. That’s because it takes time for the insecticide and other methods above to completely eradicate the pests.

As a preventive measure, you can also treat some of the other plants to keep them potentially getting infected or get rid of any eggs or larvae that may have already been left there.