Getting Rid of Fungus Gnats

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Those blasted fungus gnats!  We’ve all seen them to some extent in our houseplants.  Left unattended, fungus gnats can become a huge problem for your houseplants.  And there is more than meets the eye! 

It is not just the fungus gnats that you see flying around, but also fungus gnats larvae in the soil itself.  Fortunately though, there are some cultural practices that you can employ, as well as easy fungus gnat treatment methods that you can easily do at home to finally get rid of gnats!

fungus gnats larvae

Identifying Fungus Gnats

If you see a swarm of little flies around your houseplants, chances are, you may have fungus gnats.  Fruit flies are also commonly found indoors, but there are some key differences:

Fungus gnats are dark in color, about 1/8″ inch long, and usually have translucent wings.  They can be found swarming around plants, especially around wet soil.  More on this topic later.

Fruit flies are similar in size to fungus gnats but can easily be distinguished because they are lighter brown in color and have large red eyes.  They can be found swarming around ripe fruit, such as bananas, or other sugary foods.

Interview: Get Rid of Gnats!

Recently I  had the opportunity to interview Jackie Smith from Portland Oregon.  I met Jackie through Instagram and she had shared with me her success story in dealing with fungus gnats, so she graciously agreed to let me interview her and share her triumph! 

I hope you enjoy the interview below.  It is full of very detailed information, and if you are reading this article, you probably can relate and have gone through the same problem.  I hope you can achieve success just like Jackie has!

Raffaele:  Tell me a little about yourself.  Your name, where are you from, and what your favorite houseplants are?
Jackie:  My name is Jackie Smith from Portland, OR and I have lots of favorite houseplants but my top 5 would be ferns, rubber plants, pileas, snake plants, and spider plants.
Raffaele:  I understand that you have about 150 houseplants!  When did you start growing houseplants and how did it all start?
Jackie:  I grew up in family who all enjoyed gardening so I can’t really remember a time that I wasn’t into houseplants!  They’ve always excited me and I’ve always had a major love, respect, and passion for plants in my home.  From my very first apartment to now, I’ve always had a big plant collection that tends to always get a little out of control.  My grandma has been my biggest influencer and I was lucky enough that my best friend’s dad owns a garden center.   I remember after high school going into the greenhouse multiple times after hours, unsupervised, and he’d always let us pick out a few plants.  It was a lot of fun!  
Raffaele:  I approached you for this interview because you had shared a big success story with me in dealing with a large fungus gnat infestation in your collection.  When did you first have a problem with fungus gnats and how big did the problem actually get?
Jackie:  In January 2018, I went to a plant sale and bought several ferns that required moist soil at all times.  In the first week I started to notice a fungus gnat here and there.  At first, I didn’t think too much about it.  Within 2-3 weeks, now into February, I was starting to worry at how fast a few fungus gnats had now turned into several.
Every time I watered my ferns, so many gnats flew up into my face.  I saw their larvae in all of the soil and even ones crawling on the pots.  At this point I knew that this was a lot more serious than I had thought, and it was only going to continue to get worse.  I knew that I had to do something.
I have 3 plant stations in my living room and 2 more in my side room and everything was infested by the end of February.  My water vases/jars that held cuttings had dead gnats all around the top rim.  The infestation had gotten so bad that it was very uncomfortable to sit on the couch and was very embarrassing.  There were gnats constantly around and it was obvious that they had developed a flight path to travel to all of my plant stations and the couch was on their route.
You could see lots of gnats always buzzing around.  My windows were covered with them so badly that I would sweep up as many of them as I could multiple times a day.  I remember taking a nap one day and waking up from a loud buzzing in my face and a gnat going up my nose.  They were constantly in my face.  If I sat on the couch, I was constantly clapping my hands trying to kill them.  It was awful!
I had contemplated throwing my ferns away several times and even thought that I might seriously have to get rid of everything because the infestation was that bad and only getting worse.  I had hung 10 yellow sticky traps throughout my plant stations and they filled up fast.  By the time I changed a few of them, within a month or so, the yellow traps were completely covered with gnats again.  I learned a lot the hard way through out this process.  I just had no idea that they could and would reproduce so quickly.
Raffaele:  Tell me about some of the ways that you were able to eliminate fungus gnats.  What products did you use?

Jackie:

I started letting the soil dry completely out and watering my plants from the bottom, but didn’t notice anything positive from that.

I hung 10 yellow sticky traps, but it showed no signs of improvement with cutting down their population.  But I know they helped a lot and I was grateful for how well the yellow traps worked.  I recommend them as a tool for this type of problem, killing the adult gnats that are laying the 200-300 eggs per week.

fungus gnats larvae

I bought a 1.5 cubic ft. bag of Gnatnix and used it as a top dress.  It’s made from recycled glass material and you top dress about an inch of your plant.  It is supposed to stop the gnats from reproducing and protect the soil, but I noticed that the gnats could crawl through it very easily, and they were also going to the bottom of the pots and getting to the soil that way.  I regret taking the time to top dress all of my plants with Gnatnix because it didn’t work at all.  I’m sure that it did slow down their process but the gnats were able to adapt to the situation quickly like it was no big deal, and I was left with the ugliness of the Gnatnix on all of my plants.  I didn’t like the way that it looked at all.  It was a big project top dressing all of my plants and a big messy project getting rid of all of it.  Big waste of time and $35.

I laid out containers and jars filled with a recommended vinegar mix with drops of the blue Dawn soap because it’s supposed to attract the gnats and kill them.  It didn’t do much for me. 

I drenched a few of my ferns with a blue Dawn dish soap solution but again, no success.

By this time it’s now mid-March and I’m panicking.  I’m in a full battle with these gnats and I’m losing. After trying all of the recommended solutions from my books and the internet.  I was desperate.  I was going through a box of my garden supplies and I found a tub of this powder called Gnatrol from years ago that I had forgotten about.  Gnatrol is organic (omri) bti bacteria.  I used to be a sales rep in the garden industry and I had received it to sample and try out but had never used it.
So I researched it online and was loving what I was reading so much that I used it immediately.  I didn’t notice any positive effects from it yet and then a friend told me that it only has a 2 year shelf life and I knew that this was way older than 2 years so I found some locally and bought a tub of it.
I came home and used it like the directions said:  2 tbsp mixed in 1 gallon of water and watered it into my plants.  I was now heavy into my research on Gnatrol and I read that it is an organic BTI-bacillus thuringiensis, subsp. israelensis.  It’s a highly selective biological larvicide for use in greenhouses to control fungus gnats larvae.  Once the larvae have ingested the Gnatrol, they become paralyzed, stop feeding and die immediately.
Because Gnatrol is a bacteria, you have to use filtered water, however I was using tap water.  The tap water kills the bacteria on contact.  No wonder I wasn’t noticing improvement. The first time I was using expired Gnatrol, and the second time the tap water got me, so the third time was the charm!
I used 10 gallons of filtered water, watered all of my plants with this fresh Gnatrol solution, and was completely shocked to notice that things were improving a little after a few days.   Things continued to improve more and more with each watering.  There was hope, right when i was about to give up!
It’s now the end of April and I’m finally noticing some improvements.  A 3 month long, heavy infestation with multiple generations of fungus gnats is now disappearing day by day.  I was amazed by the Gnatrol effectiveness.
I got an empty salt shaker and filled it with the Gnatrol powder and went to every plant and sprinkled the top of the soil with the powder.
fungus gnats larvae
I just lightly covered all of the soil and then watered with plain filtered water.  If the plants were really dry I would water with plain water first to get the soil wet, and then would sprinkle the powder on the top and lightly water it in.  This basically gets the powder wet so that it’ll absorb into the soil for the larvae to eat.
For the plants that were infested the worst with the larvae in their soil, I sprinkled the Gnatrol on a little heavier.  At least 1 tbsp worth per plant in an 8 inch container, and I did this every time I watered until the problem was under control.  Since the directions call for only 2 tbsp per gal of water to be diluted and watered in together, I was hesitant and concerned about how much I was actually sprinkling onto each plant, but even on my heaviest doses I never noticed any negative impact.
I had complete success with this method and highly recommend to anyone with an infestation as bad as mine was.  I was able to save all of my 147 house plants and live completely fungus gnat free still to this day.  After all of that, my plants are thriving and growing, loving life.  I’ve been using Gnatrol this way, dry in a shaker since April, but don’t need the heavy doses anymore.  I now use it more as a preventive.  I don’t ever want to deal with that again!
Since I became gnat free in June, I have occasionally seen a gnat or 2, and whenever that happens, I get my shaker and filtered water and do a quick treatment to prevent the gnats from reproducing.  It has worked great.
Raffaele:  What are some preventative measures that you can share with the houseplant community to prevent fungus gnats?  They seem to be everywhere to some extent!
Jackie:  Fungus gnats thrive in moist soil so letting your soil dry out is good!  They feed on fungus and decaying matter in the soil so keeping your plants free of dead leaves and plant matter helps.  The most important tip I’d like to share is that at the first indication of gnats is when you need to take action. The adults lay 200-300 eggs a week so things can and will get out of control fast, especially with plants like ferns.
Potted plants can host every stage of the fungus gnats’ life cycle.  Egg, larvae, pupae and adults in multiple generations.  I myself am an organic gardener as much as possible, so Gnatrol is my go to.  For your first treatment, I would recommend watering it in as the directions advise and then keep a shaker handy to sprinkle for future waterings.  It is the only remedy that worked for me and it worked like a miracle.  I’m so grateful for Gnatrol.  I wish it had a longer shelf life than 2 years, but since it doesn’t, I wouldn’t purchase any until needed.
Raffaele:  Since your massive issue with fungus gnats, did it change the way you grow your houseplants?  How have you grown as a gardener because of this issue?
Jackie:  I would say that I gained some extra confidence which is always nice.  I didn’t think that I was going to be able to eliminate my massive issue.  There were a few sleepless nights.  Many times I thought I was going to have to give up and start over.  I love my plants, especially the ones I’ve been gifted and owned for years.  I was really down on ferns while going through my battle, but now I don’t have that issue, can continue my love for ferns and keep their soil moist and gnat free.  Dealing with fungus gnats was a positive experience for me and I’m glad that I went through it, only because I won!
Raffaele:  Any other pieces of advice that you’d like to share with everyone?  Whether it is dealing with pests, or on houseplant care in general?
Jackie:  A couple things i would like to share is that:

Tap water kills all beneficials & bacteria.

I’ve bought beneficial mealy bug predatory insects before for my cacti and succulent collection of 200 and they all flocked to the windows trying to escape, so that doesn’t work unless they can actually escape.

Diatomaceous earth (DE) is made up of fossilized diatoms, a single-celled planktonic algae that lived in the ocean.  It kills all bugs because it’s extremely dehydrating and I’ve used it to keep ants away.  The food grade is safe for people and pets. You just sprinkle it on any plant or soil but once it gets wet you must reapply once dry enough.  It has so many uses for insects and good to have on hand.

Thrips seem to be common in the houseplant world and I’ve had them a few times. Very easy to get rid of using Monterey spray.  Clears them up on the first application but I always do a second dose.

Whenever you do a foliar spray make sure you use a wetting agent like a few drops of Dawn dish soap to help the solution stick to the leaves.

Heart ferns will die if you let them dry out. Learned that the hard way!

Even if a plant is considered safe for pets, remember that it may have been sprayed with something toxic before you purchased it, so always keep that in mind.

Aluminum foil works as a good deterrent to train your cats to leave your plants alone.  I tape pieces to areas that interest them.  They don’t like the way foil sounds so it works.

The House Plant Expert is my favorite go-to reference book and I’ve learned a lot from it.

Closing Comments on Fungus Gnats & Other Pests

I hope you’ve enjoyed the interview with Jackie above.  In summary, remember the following important items:

Good cultural practices go a long way in deterring fungus gnats!   Let your soil dry out to some extent before you water again.  Fungus gnat larvae will die in dry soil.  Also, if you give your plants the light that they need, it will help them use water more quickly.  If you have a houseplant in a dark corner and keep it constantly moist, this will greatly increase the probability of fungus gnats thriving!

Gnatrol is a fantastic product for organic gardening to eliminate fungus gnats.

Yellow sticky traps are a very good tool to capture adult fungus gnats and other bugs.

Monterey spray is a very effective treatment method for thrips, and other pests, and is listed for organic gardening.

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17 Comments

  1. Denise Stout September 9, 2018
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