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If you read my December diary, you may remember that I was dealing with a pretty intense fungus gnat infestation. It’s a super common , incredibly frustrating problem for those of us who keep plants indoors. I wanted to expand my indoor vegetable garden, but before I could, I needed to get the gnats under control or I’d end up living in a very buggy house.
I’m happy to report that I am victorious in my fight against these fungus gnats. But before I talk about how I did it, let’s get to know the enemy…
(Not So) Fun Facts About Fungus Gnats
If you see tiny black, winged bugs buzzing around your plants and crawling around your soil and containers, those are fungus gnats. The adults are harmless to humans and pets, but they are super annoying. But what about your plants?
Adult fungus gnats are generally harmless in that they don’t attack your plants. They can, however, carry plant diseases with them spreading them to your plants. The larvae like to feed on your plant roots. In a grown, healthy plant, this isn’t much of a problem other than being unpleasant. However, larvae can be disastrous for new seedlings. They typically feed on rotting roots and other decaying matter, but they’ll occasionally make an exception and go after healthy plant tissue.
They love a moist environment like wet soil or standing water. This can be a problem when you’re trying to germinate seeds that also need moisture.
Fungus gnats are also hardy little suckers. They have antifreeze proteins which allow them to resist being frozen AND survive being frozen (most bugs can only do one of those). So cold doesn’t bother them at all.
Weaknesses you can exploit:
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- They are short lived: The total lifespan from egg to adult is about 3-4 weeks. If you can start attacking them at all stages of their life cycle (especially the larval stage), this problem will be resolved in no time.
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- They only live in the top inch or so of your soil: Ridding yourself of fungus gnats is not going to require major intervention. Treatments at the top of your soil should suffice.
- They love the color yellow: Maybe it reminds them of their favorite flower. Perhaps they too crave the sunshine on a cold winter’s day. Either way, let’s give them some yellow (sticky tape)! MWAHAHA!
Where I Think My Gnats Came From
Fungus gnats can come from anywhere really; bringing in plants from the outside, introducing a new bag of soil or starter plant from the store, an open window, or maybe they’ve been hiding in your plants all along but you never noticed. Now that I have knowledge and experience under my belt, it’s easy to see where I may have went wrong in my initial setup.
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- I underestimated fungus gnats’ survivability. I was counting on my area’s negative temperatures to prevent this problem. You now know that fungus gnats survive the cold just fine. And now I know. I’ll never underestimate them again!
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- I did not thoroughly clean my bean container. I purchased a couple “self watering” containers on the cheap that I used outside this summer for other plants. My suspicion is that a good amount of fungus gnats were living in the reservoir where it was super moist.
- I used soil purchased from an outdoor garden center. I didn’t think I’d have any problems with this since the bag had gotten quite cold in my garage. See #1.
- I watered too much!!!! This is a persistent bad habit of mine that I am trying to break. But in my newb panic to get my seeds to germinate, I probably overdid the watering again.
The Winning Strategy
In order to wipe out the infestation, I had to attack the gnats in all stages of their life cycle: eggs, larvae/pupa, and adults.
Yellow sticky traps: Kills adults and acts as your alarm system. The sticky traps were the first sign that I had a problem as they had been doing a great job attracting and trapping the adults. It’s not terribly uncommon for me to catch one or two, but two traps filling up with gnats in a matter of days? Trouble city! I stuck more traps throughout the soil, so I could continue grabbing as many adults as possible. As a test, I also stuck some clear packing tape on the outside of the container to see if that would trap any gnats. No luck! I guess they really do love yellow.
Sprayed and watered the plants/soil with Espoma Earth-Tone Insect Control: Kills gnats in all stages. I busted this out as soon as I recognized the infestation, and it worked great keeping the swarm in check while I figured out my next moves. The active ingredient in Earth-Tone is pyrethrin which attacks the nervous system of insects. It has an extreeeeemely low toxicity to people and pets and won’t harm your plants; so it’s safe to use. I also added a few squirts to my watering can when I watered to make sure it reached the larvae below the surface.
Stopped watering for about two weeks: Kills larvae, prevent egg hatches, and creates an inhospitable environment. Guys, this was hard for me because, in my mind, watering my plants=I love my plants! But the main reason fungus gnats typically appear in the first place is due to over watering. Go figure. So I stopped watering to allow the top layers of soil to dry out, thus making it no fun for them to stick around. Lack of moisture also prevents the eggs from hatching and kills off moisture-dependent larvae. I kept an eye on my plants to make sure they continued to look healthy and didn’t wilt.
Scooped away the top layer of soil: Eliminates some eggs and larvae. If you look really close, you might be able to see tiny white dots in your soil. Those are gnat eggs. An adult can lay up to 300 of them in their short lifetime! Scooping them out of the soil is a good way to cut down on numbers. I highly recommend disposing of any scraped soil directly in an outside container. If you can’t do that, seal the dirt in a Ziploc bag and put it in your trash.
Sprinkled cinnamon on the soil: Creates an inhospitable environment. So I discovered this in the course of trying to solve another problem. I planted basil seeds in a different pot and was struggling with mold forming on my topsoil (again, due to over watering!!!). I read a tip online about sprinkling cinnamon on the soil as it’s an anti-fungal (totally works for mold control!). But I also noticed at the peak of my fungus gnat infestation that the bugs weren’t really hanging out on the basil, just the bean plant. As soon as I added cinnamon to the bean plant, the gnats started freaking out and fleeing.
Added Bti: Kills larvae. Killing the larvae are key in reigning in the infestation and minimizing plant damage. I tried Summit Mosquito Bits based on reviews, and I’m very happy with the result. Bti (Bacillus thuringiensis) is a bacterium that is only toxic to fly larvae, including fungus gnats. So again, safe for humans and pets. I mixed the recommended amount of kernels into the soil. As I watered, the Bti spread down to where the larvae feed. This is a must have product for your arsenal. It does require subsequent applications as the Bti will dissipate.
*I also want to devote just a little bit of space to what didn’t work. A common suggestion I came across was to mix dish soap with apple cider vinegar in a small dish and place it near the plants. I tried it, and it totally failed. That’s because fungus gnats don’t care at all about vinegar or rotting/fermented fruit. You know who does?
Fruit flies! They are very similar in appearance except have a slight reddish coloring. And guess what fruit flies don’t care about? That’s right; your plants. So if gnats are hanging around your plants, they’re most likely fungus gnats. If gnats are hanging around your trash can, garbage disposal, or produce, they’re most likely fruit flies. Attack them accordingly.
About 3 days after fully implementing my strategy, I started noticing more gnats buzzing around further away from the plants (like around my lit up computer screen…gross). As annoying as this was, it was a really good indication that I on the right track of creating a less welcoming environment for them. They were on the hunt for greener pastures…
We’re in Maintenance Mode!
It took about two weeks after I started my various treatments for the infestation to disappear. I would love to say I’ve resolved the problem 100%. But this goes back to the whole underestimating the enemy thing. Fungus gnats are tough, and even though I don’t really see them anymore, they are still there. Lurking in the shadows…
So to prevent them from getting out of control again, I follow a regime that closely resembles my attack plan:
- Controlled watering plus Earth Tone: To keep my watering in check, I now use a small squirt bottle instead of a watering can. I always feel compelled to empty whatever container I’m watering with, so using a small bottle is working for me. I still add a couple squirts of Earth Tone to my watering container when I water. Hurts gnats, doesn’t hurt the plants. Win-win for me!
- Add a few more kernels of Mosquito Bits: The Bti on the kernels will eventually be eaten by larvae or dissipate. A weekly to bi-weekly application is reccomended.
- Sprinkle with cinnamon: After a while, the cinnamon from previous applications will thin out. So I pretty heavily sprinkle new cinnamon to replenish it. (Side note: I just did this today, and it caused quite a few hiding gnats to flee my basil…right into the sticky traps.)
- Replace sticky tape as needed: These are still gathering the occasional adult, but not nearly to the numbers when I was at the peak of the infestation. Once they start filling up or getting too moist from absorbing water, I replace them. Easy peasy!
So, there you go! There are a lot of different tips and tricks around the internet for controlling fungus gnats, but thus far, this is my tried and true method, and I’m quite pleased with the results. Of course, wouldn’t it be great if I didn’t have this problem in the first place? Yes!!! So my next steps, now that I feel comfortable expanding my indoor garden, is to play around with preventative measures. So stay tuned for that!
In the meantime, let me know in the comments if you’ve battled fungus gnats before and if you were able to vanquish the enemy.