How to Get Rid of Fungus Gnats in Houseplants, Organically!

Houseplants bring a dazzling, outdoorsy, peaceful energy to any home! They also help to cleanse your space by purifying the air around them. However, while you may be eager to create a jungle-esque vibe inside, you probably aren’t looking for a full immersion experience – with bugs flying all over your house! Unfortunately, fungus gnats are a fairly common problem with house plants. The good news is –  it’s easy to get rid of fungus gnats, once you know the tricks!

Read along to learn how to kill fungus gnats in your house plants. These tips can also be applied to other plants and soil too, such as in potted plants in a greenhouse, or even outdoors. When it comes to fungus gnats, prevention is key! Therefore, we’ll go over a few ways to prevent fungus gnats first, so maybe no intervention will be needed at all. Yet when you already have an infestation on your hands, there are several organic methods you can use to get rid of fungus gnats.

5 Natural Ways to Get Rid of Fungus Gnats:

• Eliminate excess moisture
• Sticky traps 
• Hydrogen peroxide
• Bacillus thuringiensis israelensis
• Neem oil

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Let’s go over each of these options! But first…

What are Fungus Gnats?

Fungus gnats include several species of tiny, short-lived flies. They are commonly confused with fruit flies, which are similar but have slightly different anatomy, feeding, and breeding habits. Rather than fruit, fungus gnats are drawn to the warm, moist, cozy environment that you’ve created for your potted houseplants. They may hitch a ride into your home on a new houseplant friend you adopt, or sneak in through doors, windows, or other small crevices in your home. 

Fungus gnats reproduce by laying eggs in the top couple inches of damp soil. The eggs hatch into larvae, the larvae feed on organic matter within the soil for 2 weeks, and then they pupate. A couple of days later, the adult flies emerge and start buzzing around. You’ll commonly see fungus gnats hanging out on the soil surface, edge of the pot, or maybe around the drainage holes of the pot. They most often only fly in short bursts, and otherwise crawl around.

Are Fungus Gnats Harmful to Plants or People?

Fungus gnats are not harmful to people, aside from being annoying! In small numbers, they are not harmful to your houseplants either. However, the University of California warns that when left unchecked, large populations of fungus gnats can become damaging to plants. Their larvae may begin to feed on the plant’s roots, which causes stress, yellowing, wilting, and potential death of the plant in the most serious cases. Fungus gnats can also spread disease that leads to damping off – a condition when young plants or seedlings suddenly wilt and die.

3 WAYS TO PREVENT FUNGUS GNATS IN HOUSEPLANTS

1) Moisture Control

As we’ve already established, fungus gnats love moist soil – and need it to breed!  Therefore, overwatering your plants can easily lead to a fungus gnat problem. To prevent and battle fungus gnats, avoid overwatering your plants in the first place. Only provide water when the top couple inches of soil has dried out. Remember, that top shallow soil is where the fungus gnats are drawn to! 

Thankfully, most houseplants don’t mind if you cut back on their water a bit. Truth be told, many plant parents are guilty of watering their plants more than they should. So much so, that overwatering is a common cause of death in houseplants!

Another good indicator of moisture control is the drainage tray or trough at the bottom of the pot. This should be dry within a day of watering the houseplant, and not have standing water. If it does, you may be overwatering! A quick-filling drainage tray could also be a sign that the plant’s soil has poor water retention, is root-bound, or that water may be running around the sides of the root ball and soil – rather than seeping through. To read more about houseplant care tips for watering, soil, fertilizing and more, check out this article – “Houseplant Care 101: The Ultimate Guide to Happy & Healthy Indoor Plants”. See how to water and care for air plants here.

2) Soil Choice & Modifications 

When potting up a new houseplant, use a reputable quality bagged potting soil. One that has been pasteurized or sterilized shouldn’t have live eggs, larvae, or flies in it.  Avoid using soil from your yard, as it may bring unwanted pests inside along with it.

After potting your houseplant, consider adding a layer of horticultural sand (not play sand!) to the top of the soil. You can water the plant through the sand, and meanwhile it will deter fungus gnats from laying eggs in the pot. In addition to sand, there are other soil-topping products like this one (made from crushed recycled glass) that are specially made to eliminate fungus gnats from your potted plants.

3) Prevent Spread

When you bring home a new houseplant, look for the presence of fungus gnats. Unfortunately, only the flies will be obvious since the larvae or eggs are very difficult to detect. It is a good idea to keep new plants away from your other houseplants for several days to monitor, especially if you have suspicions that they may be infected. Remember, fungus gnats don’t typically fly long distances unless they have to!

Therefore, keeping new or infected plants in quarantine can be very effective at reducing the spread of fungus gnats to other potted plants. That way, you can focus your treatment on just one plant instead of them all! For severe infestations, some folks may choose to completely remove the infected plant from the house. 

5 WAYS TO GET RID OF FUNGUS GNATS

1) Eliminate Excess Moisture

At the first sign of a fungus gnat issue, this should be the initial step. Allow the top few inches of the plant’s soil to dry out. This will make the soil unattractive to adult flies, preventing them from laying more eggs. If you’re lucky, this can kill a lot of the eggs and larvae too!  Furthermore, eliminate standing water. This includes in the pot drainage tray, or even from other sources nearby – such as leaky pipes, condensate puddles, and so on. 

2) Sticky Traps 

Fungus gnats are drawn to light, as well as the color yellow. Use yellow sticky traps near, hanging from, or inside the potted plant to catch adult flies. These sticky traps on stakes are designed especially for potted plants! We also hang these larger ones to catch gnats and other flying pests in our greenhouse.

However, keep in mind that fungus gnats spend the majority of their lifecycle as eggs and larvae, so sticky traps will only help a portion of the problem right away. If the adult flies have already laid more eggs, the cycle will continue. Yet reducing the adult fly population with sticky traps does help put a dent in the problem overall! Continue to use sticky traps for several weeks to fully break the cycle and get rid of fungus gnats. 

3) Use Hydrogen Peroxide to Kill Fungus Gnats

If the simple combination of drying out the soil and hanging a few sticky traps doesn’t get the job done, there are several natural and non-toxic products used to kill fungus gnats as well. One option is to use something you probably already have around your house – hydrogen peroxide! The good news? It is readily available, easy to work with, and won’t harm your house plants. The best news? Hydrogen peroxide reportedly kills fungus gnat eggs, larvae, pupae, and adult flies on contact. Sayonara, suckers. 

To make a hydrogen peroxide solution, first be sure you’re using the typical 3% household hydrogen peroxide, not the industrial-strength stuff! Dilute it down slightly and mix 1 part 3% hydrogen peroxide to 4 parts water (e.g. 1 cup peroxide and 4 cups water).

Allow the soil to dry slightly before application. Then, either spray the surface of the soil thoroughly until it saturates down a couple of inches. Or, for a deeper and more effective treatment, water the entire plant with it – soaking all of the soil. It will fizz and foam, which is totally normal. It quickly breaks down into molecules of water and oxygen, which clearly aren’t a danger for plants!

4) Biological Control of Fungus Gnats – Bacillus Thuringiensis 

Another non-toxic way to treat fungus gnats is to use biological controls, such as Bacillus Thuringiensis. Specifically the subspecies israelensis, also known as Bti.  Bti is a naturally-occurring bacterium that is found in soil. According to the EPA, Bti contains spores that produce toxins that specifically target and only affect the larvae of the mosquitoes, blackfly and fungus gnats. Meaning, it is not harmful to other organisms.

You may have heard us talk about Bt before, but note that there are a few different types of Bt! Bti is the one that is effective against fungus gnats, while this Bt product (Bacillus thuringiensis kurstaki) targets caterpillars such as cabbage moth worms and cabbage loopers, but is ineffective at killing fungus gnats.

To apply Bti, follow the instructions for a “soil drench” on the product that you purchase. It is usually recommended to water the plant with the solution, since only spraying the surface of the soil may not penetrate deep enough to kill all of the fungus gnat larvae. Repeat as needed, following the instructions. Another popular option is called “Gnatrol”.

5) Neem Oil Soil Drench

In a similar method to hydrogen peroxide or Bti, a neem oil drench can also be applied to the infected soil to kill fungus gnats. Do not use straight concentrated neem oil though! Create and apply a dilute neem oil solution by following the manufacturer’s instructions on the neem oil product you select. Watering with a dilute neem oil solution can help to kill fungus gnats, and also repel them in the future.

When shopping for neem oil, I always suggest choosing a high quality cold-pressed pure neem oil over pre-mixed products that contain a lot of other additives. In order to fully mix neem oil with water for an even and effective application, the neem oil will need to be emulsified first – because oil and water don’t easily mix. Check out our article all about properly mixing and using neem oil in the garden, or, for houseplants!

And that is how you prevent and get rid of fungus gnats in houseplants!

I hope that these tips will help you and your houseplants happily thrive, pest-free and healthy. If you are having issues with other houseplant pests such as aphids or mealybugs, check out our simple soap spray recipe to battle those buggers! Please feel free to ask questions in the comments below, or share this article with your friends. Thanks for tuning in!

For more information on garden pests, see this series of articles:

• How to Prevent Pests in the Garden
• How to Identify the Top 18 Common Garden Pests & Beneficial Insects
• Organic Pest Control: Over 25 Ways to Stop Pests from Destroying Your Garden!