Kill Fungus Gnats in Your Seedling Soil with My Secret 3-Ingredient Recipe That Works Instantly
Don't let fungus gnats ruin your seedlings! Learn the secret 3-ingredient gnat killer you already have in your cabinet.
What is the most common indoor pest? We’re talking about those tiny flying insects that materialize in flocks around your indoor plant soil… fungus gnats. If you’ve got one, you’ve likely got hundreds, and despite lots of suggestions and tips from “experts” on the internet, they are hard to get rid of.
But it is possible to get rid of these common pests without tossing out your pothos plants. And the solution is neither expensive nor difficult. Is it really a secret? Well if people knew about it, they wouldn’t be complaining about fungus gnats, would they? Get on the short list of people whose houseplants are free of this constant menace. Here’s how.
Fungus Gnat 101
What is a fungus gnat? The term refers to one of those tiny black insects that seem to hover around your houseplants in clouds. They feel a certain proprietary interest since they live there – they were born in the soil of that very houseplant and have no reason to travel far from home.
Outdoors, adult fungus gnats eat composting organic matter in the soil and lay their eggs there. Indoors, their options are limited. They head toward the moist upper soil of houseplants, feed, and lay eggs. Naturally, the young gnats grow up and hang near the houseplant. Fortunately, you don’t have to worry about bites or stings from these insects, but your plants may not be so lucky.
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Fungus Gnat Damage
Let’s be fair about this: adult fungal gnats do not harm you or your plants. They are a big fat nuisance, however, and are always unwelcome guests. And the fact that adults don’t bite doesn’t mean that the pests are harmless. It’s the young that do the damage.
While the adult gnats don’t have an expansive lifespan, they propagate rapidly and prolifically. Female gnats can lay some 300 eggs at a time in the moist top layer of the soil. These eggs hatch in about four days and quickly evolve into larvae. It is at this stage that the emerging gnats, still living in the soil, chow down on the roots of your plants. They’ll also eat any decaying organic material, like leaves that fall into the soil.
Once they mature, they stay close to the soil surface, living in it or flying around near it. Pick up your plant and they rise in a cloud.
Keeping Fungus Gnats Out
It’s not easy to block the outdoors/indoors border to keep these gnats out. They are not strong fliers, but they can still fly into your house through open windows and doors. They're attracted to moisture, and especially moist soil. So overwatering your plants or keeping around areas of standing water – whether in the sink or in a plant saucer – can be a siren song.
But it’s also typical for gnats to enter your home as eggs in the soil of new plants. It’s always a good idea to isolate new plants for a week or so when you first get them to be sure they are free and clear. If the eggs are present in the garden store, the bugs will appear in your home.
And don’t forget that gnats like and live in compost. So adding compost to the houseplant soil may also add fungal gnat eggs. Sometimes liquid fertilizer is a better idea.
Finally, bottom watering is often touted as a method of discouraging and disappointing fungal gnats. Since the adults prefer to lay eggs in moist soil at the top of the houseplant container, they will be thwarted. They cannot burrow down to the bottom of the soil, even if that’s the wet section. While this can work for succulents and cactus plants, it’s less effective for thirsty plants that need uniformly moist soil.
The Secret 3-Ingredient Gnat Killer
So let’s get to the gnat killer, with its three magic ingredients. I would venture a guess that you already have everything you need to mix up the magic. This potion requires water, dish soap, and hydrogen peroxide.
When you spray this mixture on adult gnats, the soap makes it stick to their wings and the peroxide kills them.
Obviously, you’ll have to repeat this quickly as new gnats are hatched from the eggs. Female adults can lay eggs from about a week after they are born, so that’s your timeframe. The idea is to kill them before the females lay eggs.
- Find a glass jar to mix in
- Add ½ cup of water
- Add ½ cup of hydrogen peroxide
- Add 1 tsp of soap
- Shake it up to mix it
- Pour it into a sprayer
- Set out to hunt down the gnats
Variations on a Theme
You can also use a variation of the three-ingredient fungus gnat killer to trap fungus gnats. This recipe substitutes apple cider vinegar for the peroxide. Blend one part vinegar with two parts water, then add a dash of dish soap. Place this mixture in a bowl near an infected house plant.
How does this work? The water is the “bones” of the trap, providing the liquid base. The dish soap breaks the surface tension of the water, preventing gnats from climbing out, while the vinegar is both the lure – it smells like rotting apples – and the poison.
