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Fungus Gnat Season: How To Deal With Them

Well, it’s finally upon us. With the gorgeous warm weather, the longer days and the rise in humidity comes the inevitable: fungus gnat season. Fungus gnats are one of the most common houseplant pests, and usually are nothing more than that--pests. But occasionally, a particularly bad infestation can threaten a plant (or a whole collection), so I like to keep my eye on them. And while I’ve been able to avoid them all winter long, the summer months seem to be the time of year I see them the most. Today, I wanted to write a bit about what I’ve learned throughout my plant journey when it comes to these tiny flies that inhabit houseplant soil…and some of it may surprise you. From alternative treatment options to learning things the hard way, I’m more than happy to share what has worked for me--and what hasn’t.

Fungus Gnat Lesson #1: It all comes down to water

No matter what I’ve tried, I always seem to find myself swatting away fungus gnats at this time of year. I am a chronic over-waterer (though I’m getting better!) and that is the number one cause of this particular type of pest. They thrive in wet conditions. I have learned the hard way to truly let my plants dry out between watering, to check their drain trays for extra moisture, and to adjust my watering schedule based on humidity levels. This means that my watering schedule changes as the seasons change. A moisture meter is also incredibly helpful when it comes to plant watering. Trust me when I say this: when it comes to fungus gnats, it’s best to leave the top layer of soil dry!

Fungus Gnat Lesson #2: Harsh treatment options are…harsh

When I was first dealing with fungus gnats, I went directly to internet search engines to look for treatments. I found a ton of recommendations, but decided to try a hydrogen peroxide flush to remove the gnats and their eggs. In my experience, this harsh treatment did kill the gnats…but unfortunately, it killed my plant, too. Theoretically, this treatment is ideal because it would kill the eggs, the larva and the mature fungus gnats. However, I found it really taxing on the plants I tried it with, and I lost a pothos in the process. 

My tried and true treatment options include the following:

  • Preventative neem oil treatment: I add a few drops to my watering can, and dilute it in a spray bottle to polish the leaves of my plants. Fungus gnats hate this stuff, so the idea is that the neem oil will make the environment inhospitable to the unwanted bugs.
  • Sticky traps: these traps can be placed in your plant pot to catch mature gnats on their sticky glue.
  • The apple cider vinegar trick: Occasionally, when gnats (or fruit flies) try to make an appearance in my home, I fill a small dish with apple cider vinegar and leave it out to trap the bugs. They love vinegar, and willingly fall into the bowl. It’s an easy, cheap option to help keep their numbers down. 

Fungus Gnat Lesson #3: Think about alternatives

I have begun to think about other, non-traditional ways of taking care of fungus gnats: carnivorous plants! Recently I have been doing some research on different meat-eating plants that love fungus gnats. This solution seems to be a win-win: I can keep the fungus gnat population in check in a natural and sustainable way AND I get a new plant. What could be better? A popular carnivorous plant that serves this purpose is the butterwort; its sticky leaves act like fly paper, and trap the gnats on contact. I’m looking into acquiring a butterwort for my collection, but would love to hear from you on our social channels if you’ve ever tried something similar! 

When it comes to fungus gnats, I’ve learned that sometimes it’s best to live and let live (a few of them, anyways). As with fruit flies, a bug or two won’t cause much harm. An infestation, however, is another problem. It’s best to get ahead of them while we still can. If you’ve got any genius tricks that you’ve tried, leave a comment below!

Comments (1)

  • Stacey on Aug 05, 2022

    I also had a small problem with gnats. Now, I place my pots in a small tub with about an inch or two of water for bottom watering (keeps the soil tops dry). I leave them to soak up as much water as they’d like for 20 min-1hr. depending on how large the plant is.

    I also have a monstera potted in a ceramic pot with an attached plate, making it impossible to do the soaking method. This was the plant I was struggling with the gnats! So, I took a wide, biodegradable straw (the type used for boba drinks) and I put it into the soil about 4” deep. I water the monstera through the straw about twice a week. I also sprinkled a little bit of diatomaceous earth on the top soil. Walah! No more gnats after a few months!

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