How to Get Rid of Fungus Gnats on Houseplants
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We have been getting a lot of questions on how to get rid of fungus gnats recently! Fungus gnats are more common in winter; A damp environment with lack of air circulation creates their favorite environment. They fly in your face (because they are attracted to carbon dioxide) which is particularly annoying. Last month we did a post on natural pest control for a variety of bugs including fungus gnats. But from all of the messages we’ve been getting on our facebook and instagram, it looks like it deserves it’s own post.
Are Fungus Gnats Harmful to My Plants?
Fungus gnats in their adult (flying) state, are not harmful to your plants, however their larvae can be. The larvae can harm young plants/seedlings, feeding on their roots, which can cause them to wilt or die.
Fungus Gnat Prevention
- First you definitely want to clear out any dead leaves sitting on the top of the soil. These just give them more places to hide, and keep the soil more moist, then if it were cleared.
- Make sure you are properly watering your plants. Check out our in-depth post on watering plants if you need help. Fungus gnats like when your plants are over watered, and this is the primary reason they thrive.
- If you’re able to lower the humidity in your home, do this. Maybe down to the 40% area if it is above this. Remember this will make your plant’s soil dry out faster, so you may need to slightly increase how much you water. However, the turnover of dry to moist soil, will help break the lifecycle of the gnats.
Fungus Gnat Control
Here are some solutions that have worked for me. At times I’ve had to use many of them at once to really get rid of them. The best methods for control are ones that change the environment they like. Homemade insecticides work, but they don’t break the cycle of them returning as much as you’d like. I find it’s because they all involve wetting the soil – The surviving adults, often find a way to slowly repopulate.
These are ordered in the way I think work the best:
(1) The best method: Let the soil dry out. Dry soil means the larvae cannot live, nor will they want to lay more eggs. This works very well however, your plants need water! What you can do is water them instead from the bottom, by letting them briefly sit in a pot/tray of water. The soil will wick up the water through the drainage hole like a sponge. The trick is to time it correctly so the top soil doesn’t get wet, which can be difficult. Maybe your plants are too big to do this, so here are some more options:
(2) “Top-dress” the soil with a layer of sand or Gnat Nix (which is made from 100% recycled glass). You’ll be adding about 1/4″ of either sand or gnat nix to the top of the soil. This will not only block the gnat’s from being able to get to the soil, but will also fool them into thinking the soil is dry (since sand and gnat nix do not stay wet for very long). People often top-dress soil to just give the potted plant a finished or clean look. It also helps to conserve moisture in the soil. The one drawback, is that it makes it harder to tell when the soil is dry (and then harder to tell when to water your plants). However if you have a good feeling of when to water your plants, this is not an issue. [This method also technically falls into Fungus Gnat Prevention]
(3) Heavily spray, or lightly water the soil with a mixture of:
(In a 24 oz spray bottle)
- 1.5 teaspoons Dr. Bronners castile soap (I usually recommend sal-suds for other pests, but it might be worth trying out their peppermint, lavender, citrus, tea tree or eucalyptus scents, as fungus gnats don’t like these smells). The soap will also kill any adults caught in the crossfire.
- 1.5 teaspoons of neem oil. You can also substitute this or add 1 teaspoon of orange oil, which is highly effective.
- Adding 1 teaspoon of tea tree, lavender, eucalyptus, peppermint or cedarwood oil will also help deter them from wanting to lay eggs. Sometimes I like to just make another mix of this with water, and spray the top of the soil. I think this way it layers the different mixtures, and keeps the deterring oils on top.
(4) Water with hydrogen peroxide. 1 part 3% hydrogen peroxide, 3 parts warm water. The water should fizz, killing the larvae. Remember you are technically also watering the soil, so only do this when you need to water, but you can do this every time you water. Note: This was surprisingly effective for me, however it will only kill the larvae. So it will reduce the amount of bugs, but may not do the trick by itself.
(5) Buy Yellow sticky traps which will help to kill the adults – which complements the above which aim to kill the larvae. Gnats are attracted to the color yellow. They are also attracted to light, so if you can place it near a window or light, even better. You may have read other sites recommending to create traps from apple cider vinegar/wine/beer and dish soap, this may work, but I haven’t tried this myself. If you have a big infestation I also don’t think this will work very well, but worth a shot if you like.
(6) Lastly, a fun method of control is to get some carnivorous plants. They are not the easiest indoor plants, but they will love to eat these bugs. Venus fly traps are especially fun for kids!