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by Jordan Gales
Fungus gnats are particularly pesky but common houseplant pests. They might be difficult to spot early on and multiply quickly. Fungus gnat larvae feed on the roots of plants, especially potted house plants, which can cause plants to wither and die if the infestation isn’t addressed. Separately from the issues they cause beloved plants, they are just plain annoying to have around living spaces. If you’re looking to get rid of fungus gnats, you’ve come to the right place.
What are fungus gnats?
Fungus gnats are brown or black two-winged tiny insects commonly mistaken for fruit flies, drain flies, or mosquitoes. They have a slimmer, longer body and longer legs and antennae than fruit flies. Fungus gnats are smaller in size than mosquitoes, and do not bite humans. They are particularly pesky because they don’t target the leaves or stems the way other plant pests might. Fungus gnat larvae feed on the roots, so they may be more difficult to identify during a quick visual scan.
Why do they appear?
Fungus gnats are attracted to just that: decaying organic material. Simply put, they are particularly attracted to damp soil and standing water near plants. If you are a chronic over-waterer when it comes to your indoor plants, they will plague your plants over those cared for with benign neglect every time.
What damage do fungus gnats cause plants?
Adult gnats don’t cause any damage themselves – to plants or humans. The larvae are the big problem. Fungus gnat larvae target the roots of plants as a food source, which can limit growth and even cause plants to die if the infestation isn’t addressed. Early on, infected plants may stop growing. It may start to droop. It may start to abnormally lose leaves. And finally, it may die.
Younger plants are at a higher risk of irreversible damage. Since sprouts and young plants don’t have many roots, they are more vulnerable to root damage from fungus gnat larvae. Older plants have more roots and this sheer volume can make them more resistant to permanent damage from fungus gnats.
How to know if you have a fungus gnat problem
Plants suffering from a fungus gnat infestation will show the following signs early on:
- Fungus gnats crawling on the soil surface or pot
- Fungus gnats hovering around the plant
- Abnormal drooping or shedding of leaves
- When repotting, you see tiny white specks (fungus gnat larvae) wriggling around the roots
To identify an infestation, visually check for the above signs and look first to the plants that have moist soil.
Plants such as jade plants are particularly susceptible because their soil will be frequently moist from regular watering. However, don’t discount plants that aren’t watered as frequently. Any plant that has damp soil or a plant saucer that frequently holds standing water will be a magnet for fungus gnats.
How to prevent fungus gnats in the first place
The best way to deal with fungus gnats is to prevent them in the first place, mind your plant P’s and Q’s.
When purchasing plants at garden centers, it’s a good idea to select healthy plants with vibrant colors. Inspect the plant’s foliage and avoid plants that are droopy or wilted. Do not select ones that have brown spots on leaves or stems. Unhealthy plants attract pests such as fungus gnats.
If you can visibly see plant roots before purchase, scan for tiny white fungus gnat larvae wriggling around the roots. If a plant already infested with fungus gnats is brought home, it’s only a matter of time before the affected plant causes an infestation that spreads to other plants.
Encourage conditions that are prohibitive to fungus gnats. Know your plants well and care attentively for their specific watering needs. Ensure potted plants have soil that drains properly and opt for pots with drainage holes over ones without. A 1-2″ layer of sand over the top of the soil or potting mix can also provide defense against fungus gnat larvae since it dries quickly and won’t have the tasty organic matter that fungus gnats love.
Avoid overwatering plants and err on the side of benign neglect where possible. When watering plants, use a towel to blot and soak up water in any saucers that catch water or water plants in a sink, wait until they are done draining, then move them back to their saucer. Excess water around the base of a plant is a neon sign advertising free-for-all buffet for fungus gnats.
How to get rid of fungus gnats
If the infestation is not that bad, simply drying plants more than usual might address the issue effectively. If it is a bigger issue, you may want to turn to hydrogen peroxide soil soaks, yellow sticky traps, or a combination of both. It can take several days for the full life cycle of a fungus gnat infestation to die out, so be patient.
A hydrogen peroxide soil soak is an effective treatment that will address the root problem of fungus gnats: the larvae. Hydrogen peroxide cleanses the soil and the larvae along with it. A 4:1 ratio of 4 parts water to 1 part hydrogen peroxide (3%) would be safe for plants and effective for killing off fungus gnat larvae. You can simply water the soil with your 4:1 water-hydrogen peroxide solution, being careful to avoid wetting the leaves, or set the base of the pot in the solution where the soil can be reached and allow the soil to soak it up and take it to the roots of your plants.
For an in-depth explanation about proper hydrogen peroxide soil soak, check out this video:
Yellow sticky traps such as those found here (https://amzn.to/2D7bThM) are another good way to get rid of fungus gnats by targeting the adult population. Yellow sticky traps attract the fungus gnat in the adult stage and they are unable to fly away to lay more fungus gnat eggs. Cutting yellow sticky sheets to size and laying the traps across the surface of the soil is an effective method at getting rid of an infestation over time since fungus gnats will inevitably crawl onto them. This targets the adult fungus gnats, not the larvae.
For a tutorial on making your own yellow sticky traps out of paper and rubber cement or petroleum jelly, check out this video:
Summary
Fungus gnats are a persistent pest that can damage greenhouse and indoor potted plants, especially young ones that don’t have many roots. They can be mistaken for other household pests like mosquitos, but don’t cause physical harm to humans. Drier plant conditions will avoid making a comfortable home for fungus gnats and can prevent them from taking residence in the first place. If you already have an infestation, hydrogen peroxide soil soaks and yellow sticky traps are excellent methods to get rid of fungus gnats. Happy hunting!
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Great ideas. I’ve been plagued with gnats and white flies. Set out yellow strips. Cut the foliage of plant as I put in another room. Sprayed it an insecticide. Covered it with plastic. Leaves started to die. Recut the plant. Will put sand on it. It’s a hibiscus. It should come back. Still too ciold to put outside. It bugs come back I’m just going to discard it.
Good ideas, how about adding cinnamon to the soil. I watch a gardener talking about how he adds cinnamon to his young plants to help?
I tried cinnamon on the soul of my succulents without testing it first; they all died.
I think because it became a drying agent.
Lesson for me:
Do a test before trying diy solutions.
Try to only add the cinnamon on the top two inches, not throughout the whole soil becuase you dont want it all to dry out.
Cinnamon is a fungicide, just make sure youre using an all natural cinnamon:)
I love those yellow sticky traps. I just put some out in attempt to capture the dreaded squash vine borer.
Where do you get these yellow sticky traps?
Right here: https://amzn.to/31GdHKy
You can find them at your local Home Depot.
Love the Peroxide idea. My question is, can you water the plants from the top and get same results? Some of my plant pots do not have the hole for drainage/absorption.
My pots do have holes in the bottom and I have alway done the hydrogen peroxide rinse from the top down. Although I do water my plants (that don’t have gnats) from the bottom- up.
I have one plant I’m working with now. I also spray the leaves with a Castle Soap peppermint mixture.
I haven’t had gnat for a while so I hope this still works. It does take about a week to get rid of all the gnats.
Just curious about the peroxide and what it does? And what is your recipe for your castle peppermint mixture I’ve never used anything like this but I am willing! Will it help clean the leaves of my plants too and what does it do to the soil? ☺
ik dr bronnors has a castile peppermint soap! It’s organic and u can buy it at walmart, amazon, target etc in various sizes
Our peace lilies were plagued by fungus gnats. We finally took them all out of soil and are now growing them in water. Don’t know if how long they will survive, but out gnat problem is gone.
Hydrogen peroxide doesn’t kill larvae and probably won’t help your gnat problem. I’ve treated my soil twice now with straight 3%. Literally sprayed a gnat and larvae and nothing happened. Soaked the soil in 3% to wake up to larvae crawling around on the surface…..
Moving on to a much cheaper alternative, Food grade Diatomaceous earth is said to be like walking/crawling through glass to insects. 100% safe to eat and safe to treat soil.
I tested and found the same thing. I found that insecticide spray did kill them but the ones I soaked in hydrogen peroxide were still alive. I don’t know why websites like this spread misinformation that hydrogen peroxide kills fungus gnats larvae. They also never provide an explanation as to why they claim it works?
Omg yes! I am watching the larvae have a swim in the peroxide as we speak! Even undiluted peroxide. This is rubbish!
Hi I had gnats real bad especially in my lemon tree and since I have the tree around my other plants it was bad. I started moving the dirt around omg it was infested.
Poor lemon tree,, I took a chance I put peroxide the one that comes already mix with water, from Dollar General store, praying that i dont kill my plants. I started spraying they were going crazy, the adult started flying around. I also have the stickys. I then started putting rocks the little one from. The dollar store, covered the soil completely, left it covered for a few days, went back to the rocks out moved the dirt around No Gnats!!
Hydrogen Peroxide doesn’t work at all.
Try taking it out of the pot, wash the roots in mild soapy water, put new soil in a pot with drain holes… I found that to help after spraying with Safers Insect Soap then putting the Safers owder ontop of soil incase there are other bugs in the soil…
I like the idea of sand on top of the soil…