Can we just talk about fungus gnats for a few minutes please? These little boogers are the bane of my existence during seedling season. Every year, no matter how I try to prevent them, there they are.
Fungus gnats are tiny little flying pests that are attracted to the moisture in potting soil. The adults will lay up to 200 eggs on the surface of your plants. When those eggs hatch 3 days later, the larvae burrow down into the soil where they feast on thin roots and decaying plant matter. That means they can destroy new seedlings that don’t have strong root systems yet.
After 2 weeks, the larvae have turned to adults where they emerge to start the cycle all over again! And, besides eating the roots directly, they can also spread Pythium, a group of plant pathogens that causes “damping off” in seedlings. See why I hate these things? Ugh!
There are several methods that I have tried to prevent/rid ourselves of them:
- Sterilizing the soil – this can be done several ways; either by pouring boiling water over the soil or by baking it on the oven at 1 80 0 for 30 minutes. While this method works well, the problem we have come across is the plants we bring in to overwinter…their dirt is not sterilized and can, therefore, contain fungus gnats eggs.
- Fly Strips – again, these work to an extent. They do manage to snag some of the gnats but they are messy and there is no long term effect.
- Mosquito Dunks – these little “donuts” can be purchased through most stores starting in mid to late Spring. They contain a bacteria BTI, which is short for Bacillus thuringiensis israelensis, that kills at the larval stage. To use, soak one donut in approximately a gallon of water for 24 hours then water plants with it. I have never gotten Mosquito dunks in time to use them right away so I am always behind in my fight. This year, I bought extra so I will be using these as soon as I plant my seeds!
- Water from underneath – because the gnats like moisture, by watering from underneath, the tops of the pots stay drier. From my experience, this works…ish. It certainly doesn’t hurt.
- Cinnamon – sprinkle cinnamon on the surface of each plant to get rid of the fungus. I’ m going to say this didn’t do anything for me.
- Peroxide Solution – water plants with diluted peroxide. I tried this last year and I obviously didn’t get the ratio correct because I killed a bunch of my plants. So I won’t be trying that again
There are a ton of other thoughts as how to get rid of fungus gnats from coffee grounds to vinegar, parsely to potatoes. I am exhausted and frustrated and can’t afford to lose my plants to these jerks! We depend on our veggies and herbs to not only refill our supplies but to also supplement our income.
So if anyone has and tried and true methods, please help a sister out here!
RJ Homestead 
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