The dreaded fungus gnat is one of the most common pests houseplant parents deal with! As such, this annoying insect has earned the honor of being discussed first.
This post will cover how to get rid of them, what they are, where they come from, whether they can damage your plant, AND how to prevent them.
Table of Contents
- What are fungus gnats?
- Where do they come from?
- Can fungus gnats hurt your plants?
- How to get rid of fungus gnats:
- Amazon Affiliate Links to Fungus Gnat Control Supplies:
- A cheap, easy, and effective way to take care of fungus gnats:
- Related Posts
What are fungus gnats?
- Small, flying insects that live and reproduce in moist, shady areas –which makes the surface of your houseplant’s soil the PERFECT home for them
- Adult fungus gnats, those you see flying around when you disturb the soil, live 7 to 10 days
- Adults lay eggs in the top inch or so of soil and the larvae feed on fungus and decaying matter within the soil
- One adult female can lay hundreds of eggs, quickly making a small fungus gnat situation into a large, annoying problem
Where do they come from?
- These tiny insects can come from MANY places
- Adults can fly in through windows or doors
- Adults can ride in on new plants; larvae can come in new plants or in new soil or compost
- Because they thrive in damp areas, plants that need to maintain some level of moisture or plants that are overwatered are particularly prone to fungus gnats
- Once you have them, they are hard to control because they only need a small amount of damp soil to survive, reproduce, and thrive! Yuck!
Can fungus gnats hurt your plants?
- Adult fungus gnats cannot hurt your plants; they just annoy us humans and do a very good job reproducing
- The larvae can damage roots and stunt growth, especially of young plants, but the number of larvae needs to be quite large to do significant damage
How to get rid of fungus gnats:
The best way to get rid of them is to take a multistep approach.
You have to control adult fungus gnats to stop those pesky gnats from flying around your house and laying hundreds of eggs.
You also want to control the ever-growing population of larvae that are feasting on your plants’ soil and roots (and eventually becoming those annoying adults).
Once both the adults and larvae are under control, then you can put measures into place to help prevent fungus gnats from reoccurring in the future.
There are many ways to achieve each step. I will list the ways that have worked for me and other ways that houseplant experts recommend so that you can choose a method that will work for you!
Think of the next three sections as a menu with three courses. Choose something that you like for each course to successfully eradicate fungus gnats!
Step 1: Controlling Adult Fungus Gnats
Option #1 Sticky Traps
Sticky traps catch adult fungus gnats by attracting them with sweet, sugary scents.
The sticky traps are placed directly in or next to the plant, as the fungus gnats do not go far from the plant. This may require you to buy multiple traps if you have many plants spread throughout your home.
Option #2 Diatomaceous earth
Diatomaceous earth is an organic powder that sticks to the gnats and immobilizes them.
You mix it into the top inch of soil for each plant. When the gnats dig into the soil to lay eggs, consume fungus, or emerge, it prevents them from continuing.
Option #3 Pumice stones
Pumice stones are a porous material that can be purchased online or in the soil section of greenhouses and hardware stores. You can add a layer of pumice to the top of your soil.
This creates a hard, rough surface which the adult gnats would need to climb through to lay eggs and dig into the soil. They do not like materials that scratch their bodies and are less likely to lay where pumice is present.
Option #4 Vinegar Traps
Vinegar traps are a mixture of apple cider vinegar, water, dish soap, and sugar. The smell of the vinegar and sugar attracts the fungus gnats to the liquid, but upon entering the soap prevents them from leaving.
To prepare the trap, mix all ingredients: .5 cup warm water, 1 tablespoon apple cider vinegar, 1 tablespoon sugar, a few drops of dish soap.
The liquid must be at least a quarter-inch deep (I usually use about a half-inch) and the trap must be placed near the plants you are trying to attract fungus gnats from.
Depending on the size of the containers you use, this can make many traps. I’ve made between 9 and 12 from one batch. I use empty baby food jars and place several near areas with plants. It is been very effective!
WHAT I DO: To control adults, I generally use a combination of vinegar traps and pumice stones. Pumice stones help slow the gnats down from laying eggs and the vinegar traps do a pretty good job of catching a good amount of adults. I do put the traps in MANY places. Anywhere I have plants, there is a trap. If the plants span more than a couple feet in one area, there is more than one trap. I find this is necessary or the gnats won’t go far enough to know it’s there.
Step 2: Controlling Larval Fungus Gnats
Option #1 Beneficial nematodes
Beneficial nematodes are a microscopic organism that feeds on the larvae of fungus gnats. It is delivered to you in a dormant, refrigerated form that looks like a powder. They are not harmful to humans.
How to use: During early morning or evening, you will
- Water your plants with a small amount of water to moisten the soil (so it is ready to absorb the nematodes);
- Mix the powder in with the recommended amount of water per instructions on the package
- Water your plants with the nematodes and they will get to work!
Within a week or so, adults should stop appearing because larvae are gone.
Option #2 Mosquito bits
Mosquito bits contain a bacterium that is poisonous to fungus gnat larvae when eaten.
One recommendation to soak mosquito bits in water (2 tablespoons of mosquito bits to a half-gallon of water). Then you can water your plants with the mosquito bit-soaked water once per week for three weeks.
Another recommendation is to shake some mosquito bits onto the plant’s soil surface or mix the bits into the plant’s soil, allowing the larva to feast on the bits directly, eventually controlling them.
Option #3 Hydrogen Peroxide
Hydrogen Peroxide can also be used in a solution of 1 part 3% hydrogen peroxide to 4 parts water. When plants are in need of watering, use this solution to water each plant. The soil will fizz for a short time and eliminate the fungus gnats on contact. You can safely repeat if needed.
WHAT I DO: I use beneficial nematodes. I prefer to use something that would be found in soil in nature. After watering all of the plants with beneficial nematodes, the adults stop appearing within a week or so. I don’t usually see them again unless I buy a plant or soil that has eggs or an adult riding in on it. The only downside is that I haven’t been able to find them locally, so I do have to order them online.
Step 3: Preventing Fungus Gnats in the Future
- Let the soil dry out before watering – Most plants actually prefer to be dry or mostly dry before being watered anyway, so this will help your plants and controlling fungus gnats. Since fungus gnats need moist soil where fungus and decaying matter are present to eat and reproduce, letting the soil dry out deprives them of their place to live.
- Quarantine new plants – Having a place in your house where new plants can be for a short period of time is ideal so you can monitor the new plant for pests (like fungus gnats) and allow the plant to begin to acclimatize to your home. If you begin to see fungus gnats or other pests, then you can treat that plant without having an outbreak among all of your plants.
- Pretreat new plants and new soil – Rather than waiting to find out whether a plant’s soil is infested with fungus gnat larvae or eggs, you could pretreat by mixing mosquito bits into the soil or by watering the plant (when its ready) with a hydrogen peroxide solution (as described in Step 2).
WHAT I DO: I let almost all of my plants dry out completely (which is what they need and prefer anyway) which takes care of the vast majority of the issues. I also quarantine all new plants and monitor new plants for fungus gnats. While I do pre-treat new plants with a diluted neem oil and soap spray for other pests (which I will cover in a future post), I don’t believe this to be an effective control for fungus gnats. So I prefer to just monitor and treat with a hydrogen peroxide solution if needed.
Amazon Affiliate Links to Fungus Gnat Control Supplies:
A cheap, easy, and effective way to take care of fungus gnats:
- Buy Sticky Traps and set them up in the affected plants to catch the adult fungus gnats
- When your plants need to be watered next, water the plants using a solution of 1 part 3% Hydrogen Peroxide to 4 parts water. This solution will fizz for a few minutes and eliminate the fungus gnat larvae on contact.
- Make sure to allow the top 2 inches of your plant’s soil to dry out before watering in the future to prevent providing a space for fungus gnats to live.
That’s it! You can repeat these steps if needed!