I have tons of indoor plants and every year about February and March fungus gnats begin to appear. Personally, I have tried every method most recommend but with no success. See how I control fungus gnats effectively and safely!
How to control fungus gnats is easy, natural and ongoing. I started to name this post How to Get Rid of Fungus Gnats but that was misleading because you don’t ever truly get rid of them. But first…
What Are Fungus Gnats
Fungus gnat adults are the grayish black, delicate little winged critters that resemble fruit flies or tiny mosquitoes. They love humid and moist conditions. The adults are harmless but the larvae feast on fungi, plant root hairs and other organic materials when they hatch. They are most harmful to seedlings, young plants and cuttings.
You may notice adults flying up when you water your plants.
Why Fungus Gnats Persist
Fungus gnats persist because new plants you bring home and potting soils all have them. Gardeners can’t get away from it. It is part of the great circle of life, especially if you are an organic gardener. Potting soils purchased at garden centers, big box stores and so on are all stored together. The potting soils are moist and full of conditions fungus gnats love to breed in. It is no ones fault. Fungus gnats are not because you over water. I roll my eyes each time I see someone say that.
(case in point, I was rid of the fungus gnats in my home, I suddenly noticed I had them again and wondered what was going on. Then I remembered I had brought home some herb plants that were on sale at a great price at a big box store and had placed them on my kitchen window sill until I could get them re-potted and into the greenhouse to grow on. Sure enough they were infested with fungus gnats.)
What Hasn’t Worked for Me
When researching how to handle fungus gnats I came across many methods that sounded good but did not work for me when I tried them. (others may have found them effective, but I did not)
- Letting the soil dry out. This did not work because a few of my plants got stressed and showed signs of it by getting brown leaf tips like my Peace Lily (Spathiphyllum) Also new cuttings just rooted and planted needed to be kept moist to grow best so letting them dry out to the first two inches was going to be a death sentence for them.
- Removing top soil and replacing with sand. If you get potting soil that is already infested then the larvae are deep enough to be noshing away. It is supposed to discourage the adults from laying eggs and continuing the cycle but if you read above on why fungus gnats persist you will see why this is just added work. I did try it though but did not get the results I wanted. The rascals started to go in along the bottom drain hole instead of on top.
There are a couple things I have not tried which are an organic pesticide soil drench (Neem, I have it but don’t use it for plants in my home as I don’t care for the odor of it) or beneficial nematodes.
What has worked for me.
Crazy as it sounds sometimes I pasteurize my soil if I notice an excess of fungus gnats before potting up sensitive plants and cuttings that can’t take the bit of root chewing the fungus gnat larvae may inflict. Do I always do this?
No, but it has been effective for so many problems. Buying sterile seed starting mix takes care of the need to pasteurize but I was starting seeds on a larger scale and wanted to use my own compost mix.
Not only does it get rid of the larvae present in just about any potting soil out there but it will also get rid of the pesky bacteria that can cause damping off when you start seeds. This temp is enough to get rid of the bad organisms without killing the good.
How to Pasteurize Soil
Pre-heat your oven to 200 degrees Fahrenheit. Pour up to 4 inches of your potting soil into a large baking pan (I like the large aluminum ones you can get at the Dollar Store) and put a meat thermometer in the center of the tray, deep into the dirt. Place the tray in the oven and keep an eye on the dirt’s temperature. Once the center of the dirt reads 160 degrees, bake for 30 minutes. Allow the dirt to cool thoroughly before using.
My Main Weapon
Sticky traps. Yep, these simple little yellow pieces of sticky paper. They keep the population of adults down so they cannot lay eggs and repeat the circle of fungus gnat life.
They come with little wire spikes to stick them into the soil but I just peel one side of the paper off to reveal the sticky stuff and lay it on an edge of a pot that I have noticed gnats swarming up from when watering.
On my plants inside the house I see an outbreak typically the end of February and beginning of March so I set out traps.
After a few days I see them starting to pile up on the traps.
To control fungus gnats inside my greenhouse I keep sticky traps out all year around. My greenhouse is where I re-pot plants, start seeds etc and I have my bags of potting soil or mix my own from my compost so fungus gnats get brought in constantly. (I don’t like the odor of Neem drench so I don’t use it in my greenhouse either)
It sounds too simple but that really has been the easiest and most effective method to control fungus gnats. I purchase my sticky traps at a local garden center. They can also be bought from Amazon and box stores. Not only do they work for Fungus Gnats but also White Fly, Aphids and Leaf Miners. More bang for the buck! Some people make their own but the traps are so inexpensive that it is not worth the bother to me.
Some have mentioned that the traps can catch beneficial insects too but I have not really had that be an issue. Mostly I only catch the fungus gnats and recently a spider.
Be gone you pesky gnats!
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