Fungus Gnats, Getting rid of Fungus Gnats


Posted by John Minton | Posted in Animal, How to's | Last Updated March 1, 2014

Fungus Gnat

I never really thought I would have pest issues, especially inside my house where I keep the most of my potted plants. But I, unfortunately,  bought a bag of Kelloggs brand potting soil from Home Depot and received an infestation of small Fungus Gnats. Not that the Kellogg brand is to blame – when bags have holes in them they can start an infection of pests from any source – even from other brands they sit next to at the store. I’ve also seen friends receive these same (or similar) pests from potted plants bought at Eisley Nursery in Auburn. It can literally happen to anyone, anywhere…

The Fungus Gnats are the size of regular Fruit Gnats, you know, the kind that go crazy when you leave out ripe fruit (and when you disturb the fruit, they fly around all crazy like?) These flys didn’t really seem to bug (pun not intended) any of the established plants but they appear to eat up many of the new sprouts I planted pre-Spring. Also, they are really annoying. They lay their eggs in the soil at a fairly rapid pace, after a few weeks inside the house they start swarming like mad….They also showed up in the bathroom, around the kitchen and in the cupboards…found myself breathing them in and drinking them in my water cups. I had enough!

Fungus Gnats life cycle

Fungus Gnats life cycle

I moved all my plants outside for a few days away from the back door (checked the weather, no freezing expected) while I cleaned out all the fly’s still in the house. After a couple days the house was back to normal – I used the sticky fly strips you hang from the ceiling to kill THOUSANDS of these Fungus Gnats, little flying choking hazards! I unpotted all my plants and cleaned all soil from the roots and root balls, and re-potted at a separate location with new pots and new soil. I then came back home and cooked the old soil with my oven to rid myself once and for all of these Fungus Gnats.

I read that some people cook their soil outside with the sun – in a box w/ tin foil on the sides and a glass top, but if your only doing a small amount of soil you can use your kitchen oven just as well. Preheat the oven to about 250° F, make sure your soil is very moist (add water through out the medium if needed but avoid making dirt soup). Cook the soil until it has heated to your set temperature through out, or at least hot enough to kill any living thing contained therein (usually 15-20 minutes in the oven is enough if you spread the soil on the thin side). When I was done cooking my soil I dumped it into a 5 gallon bucket outside and let it cool. Be careful, steam can come off the soil and burn you and it was hard for to avoid when I did it.

I later used the soil to plant some potted plants, this time without the pest infection! I mixed in some compost I had made and some earth worms to get the microbiology and other life sustaining biology back into the soil. It’s actually a lot of work to re-pot plants and cook the soil. I don’t recommend doing it unless it’s a last resort. But for my soil saving effort, it was worth it to me – at a time when I had a very tight financial situation.