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Eliminating Fungus Gnats: 3 Easy Steps for Your Houseplants

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Have you been struggling with fungus gnats infesting your houseplants and are desperate to get rid of them? If so, you’ve come to the right place! I will give you the complete picture of how to get rid of this nuisance pest. There are many remedies out there, but I will share ones that I have personally used and know that work.

Most of the solutions provided are organic solutions, but I will also discuss other methods. You can use your own discretion in terms of what you’re comfortable with.

fungus-gnats-houseplants

FUNGUS GNAT LIFE CYCLE

Before I get into how to eliminate fungus gnats from your houseplants, it is very important that you understand their life cycle, and also the conditions that help them to thrive.

Once you understand this, the 3 main things that you need to do to eliminate them will make more sense, and you will be more inclined to take all the necessary steps!

According to Cornell University, the lifecycle for fungus gnats consists of:

  • ADULT: Flying adults will only live up to 8 days.
  • EGG: The adult females then lay up to 200 eggs on the surface of the potting mix and they can about 3-6 days to hatch.
  • LARVA: The eggs then hatch into Larvae and will start feeding for about 2 weeks.
  • PUPA: Finally the Larvae pupate for 3-7 days and the adult fungus gnats emerge and starts the cycle all over again.

The temperature that your houseplants are growing in greatly affects the length of the life cycle. Lower temperatures will cause the life cycle to take more time.

fungus-gnat-adult
Adult Fungus Gnat
Photo Credit: Andy Murray, CC BY-SA 2.0

Cornell University also states that the optimal temperatures for fungus gnat development is about 70-75F. I found this really interesting because I seemed to validate this in my own home!

I’ve only noticed fungus gnats in my basement (where I have a grow light set up) and the temperature stays around 74-75F. In my sunroom, which normally stays in the upper 60s F, I’m not sure I’ve seen a single fungus gnat there.

Lastly, fungus gnat larvae mostly hang out in the top 1-2 inches of your potting mix and they like moist conditions so if your potting mix never dries out, you are helping to proliferate the problem!

Why is all this necessary to know? Because you need to attack on all fronts in order to effectively control fungus gnats.

3 STEPS TO GET RID OF FUNGUS GNATS

There are 3 main things you need to do in order to effectively control fungus gnats in your houseplants:

  1. Control Your Cultural Conditions
  2. Capture Adult Fungus Gnats With Traps
  3. Treat Potting Mix to Kill the Larvae

If you only see a couple fungus gnats here and there, it’s really not a big deal, but sometimes you will be surprised just how many fungus gnats you can have once you start to trap them!

Fungus gnats are called “fungus” gnats because they feed on fungi growing in your soil or potting mix. Adult fungus gnats are harmless, but the larvae in the potting mix, if present in large numbers, can damage roots, particularly in younger plants.

CONTROL CULTURAL CONDITIONS

TEMPERATURE

Like I mentioned earlier, 70-75F (about 21-24C) is optimal for fungus gnat development. You may not have too much control over this factor, but it is worth noting.

MEDIA TYPE

Also worth noting is that fungus gnats get their name because the larvae in the potting mix/soil feed on fungi and other microbes. They will naturally be more attracted to mixes that have compost, blood meal, kelp, etc. because there are a lot of microbes (which are also extremely beneficial for plant growth so it is a catch-22).

This is not to say that you should avoid organic mixes, because I think you can successfully use mixes like this, but is also worth noting. There are some wonderful potting mixes that include compost and organic materials.

POTTING MIX MOISTURE

What you can control that will have a huge impact on fungus gnats is the degree to which you let the potting mix dry out. Fungus gnats thrive in moist potting mix, especially in the top inch or so of your pot.

In order to manage fungus gnat larvae from proliferating in your pots, allow the top inch of the potting mix to dry out before thinking about watering again.

By allowing the top portion of your potting mix to dry out, you’re making it less hospitable for fungus gnat eggs and larvae, and this will result in less gnats that will reach adulthood and pester you and your plants!

CAPTURE ADULT FUNGUS GNATS WITH TRAPS

While you are controlling your potting mix moisture, you will need to also trap any of the adult fungus gnats. Fungus gnats are weak flyers and you will see them normally flying pretty close to your plants.

It is critical that you capture the adults so that they won’t continue to lay eggs in your potting mix. There are a number of sticky yellow traps available.

Adult fungus gnats are attracted to the yellow traps, and once they land on them, they stick to the traps and aren’t able to fly away.

fungus-gnats

Pretty gross looking right? This is essential though since you need to trap all the adults that you can so that they can no longer continue to reproduce.

I buy my yellow sticky traps on Amazon. Simply bend the yellow sticky paper and insert it on the clip so that the sticky side is on the outside, and insert the plastic rod into the potting mix in your pots.

There are quite a few different kinds of yellow sticky traps, including ones that you can hang, so just choose one that works for you.

However, if all you’re doing is placing yellow sticky traps and not doing anything else, you will not get rid of your fungus gnat problem.

TREAT POTTING MIX TO KILL THE LARVAE

The last step that you’ll need to take is to treat the potting mix to kill the larvae so that they don’t turn into flying, adult fungus gnats.

There are some home remedies which I haven’t tried so I can’t speak to their effectiveness, but here are two very effective methods to kill fungus gnat larvae in your potting mix. One is a biological control, and the other is a systemic pesticide.

BIOLOGICAL CONTROL

If you are opposed to harsher treatments, one excellent product to use is Mosquito Bits. Mosquito bits are basically corn cob granules which are coated in BTI bacteria (Bacillus thuringiensis subspecies israelensis).

Always read the label for any of these products for proper use. When BTI is eaten by fungus gnat larvae, it kills them. Under proper use, BTI is not toxic to people and will not harm pets.

I buy my mosquito bits on Amazon. Refer to the label for directions, but all you have to do to treat fungus gnats using mosquito bits is to sprinkle them on the surface of your potting mix until there is a layer completely covering the surface.

Water as you normally would, and each time you water, you’ll release BTI into the potting mix. The fungus gnat larvae feed on it and then die.

Repeat this process once a week for at least 3 weeks. You can even do it for a full month to be safe. Remember that you must be persistent with any pest control and it is a good idea to treat even after you don’t see anymore pests.

SYSTEMIC CONTROL

Another option is to use a systemic insecticide. Unfortunately, these are not available everywhere and some countries don’t allow their use.

I sometimes use Bonide Systemic Houseplant Insecticide and it is very effective to kill fungus gnat larvae. You simply apply it to the potting mix as directed on the label and water it in.

The insecticide is then absorbed all throughout the plant. Not only does it kill fungus gnat larvae, but it will also help to protect against many other pests. Protection will last up to 8 weeks.

With some other pests, I often use Bonide Systemic Houseplant Insecticide in combination with sprays to add a little more “oomph” and it works very well.

FUNGUS GNAT TREATMENT SUMMARY

In order for effective control, you must do all of these items simultaneously:

  • Control your conditions so that you don’t encourage a proliferation of fungus gnats. If you allow the top inch of your potting mix to dry out, it will go a long way in controlling them.
  • Capture the flying adult fungus gnats using sticky traps so that they can’t lay eggs in your potting mix and continue the life cycle.
Garsum Sticky Houseplant Traps Gnat Yellow Insect Trap Indoor Fruit Fly Stakes Trap(21 Traps)
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Safe and non-toxic way to capture pesky, adult fungus gnats, thrips and other flying insects.

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05/18/2021 11:53 pm GMT
Summit Responsible Solutions Mosquito Bits - Quick Kill, 30 Ounce
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Environmentally sound biological control for fungus gnats.

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05/18/2021 09:48 am GMT
Bonide Product 951 Systemic House Plant Insect Control (2 Pack of 8 Oz.)

Kills a variety of houseplants pests including fungus gnat larvae for up to 8 weeks.

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If you do all 3 of these things, you will have gone a long way to minimize huge infestations. Be diligent for 3-4 weeks, and you can be successful!

Have you dealt with fungus gnats? Comment below. Interested in how to treat other pests? Check out my other posts on:

Scale on Houseplants: 5 Effective Steps to Eliminate Them

Spider Mites: 3 Things You Can Do To Stop Them

Please do me a favor and share this post to social media because it will help me spread the Ohio Tropics houseplant care tips to the masses! Also, check out my shop on Amazon for all your houseplant care needs:

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Cathy

Monday 26th of April 2021

I had a very bad fungus gnat problem. I tried sprinkling mosquito bits on top of the soil then watering, but it wasn’t doing much and the bits looked moldy after a few days. I used cheese cloth to make little pods with 4 T of mosquito bits to a gallon of distilled water. I let it sit overnight then watered my plants with it. I also used the yellow sticky traps for the adults. It did take about 3 weeks but they are now gone! I didn’t know about the Bonine systemic insect control product until I read your article. I will try it next time. Thanks for all of your articles. They have helped me keep my plants healthy!

Raffaele

Monday 26th of April 2021

Hi Cathy! Thanks for sharing your tip with soaking in distilled water, and I'm very happy that you find my blog useful! I'm glad you were able to get rid of the fungus gnats.

Heidi

Saturday 20th of March 2021

Thank you so much for such an informative site! A few months ago I realized I was overwatering which was definitely contributing to a gnat issue in at least one room in the house. So....I decreased the watering schedule around here. In tandem with reduced watering I sprinkled some diatomaceous earth on the top of the soil in the affected pots, figuring it works for garden critter reduction so why not try it for these. Happy to report it does help quite a bit. I need to do another treatment, as it's been about 3 weeks and I noticed a couple gnats flying around the last couple of days.

Raffaele

Wednesday 24th of March 2021

Glad you're enjoying my site Heidi! Be sure to also use yellow sticky traps in order to catch the adult fungus gnats so that they can't lay anymore eggs in your plants :-)

Colleen

Monday 8th of February 2021

What about neem oil? I read about it all the time.

Raffaele

Monday 8th of February 2021

Hi Colleen, I'm personally not a fan of Neem oil for various reasons, though it can work for some pests. Even if it does work for the adult fungus gnats, it's not really practical. It would only be for the adult flying gnats, and you'd have to spray constantly and still need to kill the larvae that are present in the potting mix anyway. It's definitely not a practical solution for fungus gnats. Hope this helps!

Dorothy

Tuesday 2nd of February 2021

I have used Ceylon cinnamon to keep the larva off the roots. Looks to be working. Certainly smells good.

Raffaele

Tuesday 2nd of February 2021

Good to know! :-). I haven't tried that.