Fungus Gnats in Potted House Plants – Get rid of them!

Fungus Gnat - A house plant nuisance

What is a fungus gnat you ask? A few weeks ago I was watering one of my plants and noticed that it was swarming with flying bugs. What the heck? Gross. Every time I moved a leaf, what seemed like dozens of bugs would fly up out of the plant. Fruit flies, I thought, and put out a dish of apple cider vinegar covered with plastic wrap poked with holes. Works every time.

Except this time, I checked back the next day and there were no fruit flies. After some Googling I realized I wasn’t dealing with fruit flies, these bugs were fungus gnats.

Do fungus gnats bite? Will fungus gnats kill my plant?

Fungus gnats are bugs that resemble tiny flies. To me they look like fruit flies or miniature mosquitoes. They basically spot some moist soil, get busy with each other, lay their eggs in there and next thing you know – you’re living in a version of the Birds but in miniature.

From my research, fungus gnats do NOT bite and they likely will NOT kill your plant. They are more of a nuisance. Their larvae may eat the roots of your plant, stunting it or causing it to wilt. If your plants all live close together the infestation can also spread among them.

Even if fungus gnats don’t bite and they won’t kill your plants, who wants potted plants full of gnats? No one. They’re gross. And they fly in your face when you’re working on your computer.

How to get rid of fungus gnats in potted plants

Let me tell you, I have found a lot of information on how to get rid of fungus gnats, but not all of it has been helpful in my experience. Some sites recommend killing fungus gnats with vinegar. I tried the dish method that always traps fruit flies, but it did not work with the gnats. Also – when killing gnats you want to target the larvae along with the adults.

Here’s what worked for me and details on each step below.

  1. Re-potted one of the worst plants
  2. Let the other potted plants dry out until the surface soil was dry
  3. Sprayed the surface soil of each plant to soaking with neem oil
  4. Covered each plant’s soil with some kind of soil cover
  5. Put in a few yellow sticky traps
  6. Isolated the worst offender

Replace the first inch of soil

Hahaha. What? I read that you should take off the first inch of soil and replace it with sterile potting soil. What sorcery is this? How would one go about such a thing? So instead I completely re-potted the plant that had the worst infestation and crossed my fingers that it would work.

Dry out the soil

I just got to a point with my plants that I remember to water them and they don’t die and everything I read about fungus gnats said that they came to my plants because they like moist soil. Well how the heck are you supposed to water your plants but not have moist soil?  I tried to follow this advice by letting the soil really dry out before I watered it again. Supposedly, if you catch the adult gnats and dry out the soil, they will find your houseplants to be less welcoming and move onto wetter pastures.

Jen’s hot tip – Fungus gnats near your face? They’re attracted to the carbon dioxide you breathe out. So, if fungus gnats are flying around your face when you’re typing on your laptop or computer, you can put on a fan to blow the air around your face. Super simple right? These gnats are annoying but weaklings that can’t fly in a breeze.

Kill fungus gnat larvae

So if you can’t dry them out, allegedly you can kill them. I read about putting pieces of potato on the plant’s soil, which the larvae will then eat and you can throw out the potato along with the feeding larvae. I mean that’s some gross stuff right there, that I just don’t know if I can get down with.

I read you can also spray/soak the surface of the soil with neem oil and it will kill the larvae. Neem oil seems to be the answer to most pest issues on plants, so I went with that. I sprayed the surface of each of my plants with neem oil spray until it was soaking. Which made it wet, which confused me, because gnats like wet soil. So maybe this was setting a trap? I don’t know – I did it and it seemed to work, or at any rate made me feel better.

Cover the soil of your houseplants

Orchid Bark covering the soil of a Wandering Jew

Orchid Bark covering the soil of a Wandering Jew (T. zebrina)

I read that part of keeping your soil dry is keeping it covered with a soil cover that would stay dry. This apparently TRICKS THE GNATS into thinking your potted plant is an arid death zone.

Some of my plants do have Spanish moss around the top (which I thought kept moisture in – but whatever). I think it looks nice like little hobbits might live in my plants.  So, I got some soil cover: decorative gravel for my cactus, sheet moss, and orchid bark for my other plants. After the soil dried out some, I made sure each plant had some kind of soil cover.

I think this makes the plants look like a more appealing home, but apparently I don’t share gnat’s aesthetic values.

Gnat trap

Gnat Stix - Yellow sticky traps to catch gnats in your house plants

Gotcha suckers! Gnat traps or yellow sticky traps for gnats are super sticky yellow paper that you can either hang up (on outdoor plants) or stick into your soil on an enclosed wooden stick. This is dead simple in that the adult gnats fly into them, stick to them and die. Fewer adult gnats mean fewer baby gnats get made and this helps eliminate the adult population.

Full disclosure – a yellow card on a stick covered in dead gnats is not cute. Not a good look. But neither is a house full of gnats. It’s worth it and somewhat satisfying to see the hard evidence of the gnat eradication

Separate, quarantine, or cut your losses

The last thing I read was that if only one plant is infested, you should separate it from your other plants. I did put my spider plant in time out. It sat by itself in a corner surrounded by a cloud of gnats. It already looked sickly and now it was also gross.

I read one cut throat article that suggested if your plant is really infested, just get rid of it. Game over. Start again.

Did I eradicate the fungus gnats in my potted plants?

Yes and no. My one wandering jew plant which lives in my kitchen is now gnat free. This is the first plant I noticed the gnats on. All the steps I took got rid of the fungus gnats on that plant and in that area of the house.

My window in my dining room where my other plants mostly live still seems to have some gnats flying around, but I don’t think they’re infested – these may still be stragglers. Each yellow card has a disgusting amount of gnats on it, so I feel like that is a success. I’m going to go through and do another round of neem oil soaking to hopefully take car of any larvae that didn’t die or have been laid on the soil since the last round of spray. I’m also going to replace the cards to see how the adult infestation is progressing. If I catch fewer, I’ll know it’s working.

Alas, my spider plant – which had looked worse for wear before the gnat infestation was not salvageable. The plant already looked to be on death’s doorstep and it was overtaken by gnats. In the end I sacrificed the one for the good of the many and threw it out. It’s ok to give up on a $4 houseplant sometimes and start over. They all can’t be winners.

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