I actually had better luck with sugar water and a couple drops of dish soap in a saucer or small bowl. Left it out and it collected a lot of gnats. Hydrogen peroxide + water in the soil also helped. Neem oil is fantastic too, if you have any on hand.
Add some ripe fruit (such as bananas or grapes) to a bowl with 2 cups of water and a few drops of dish soap. Just make sure there is more fruit than water. Cover the fruit and water bowl with cellophane and poke holes in the top for the gnats to enter. The gnats can't escape the way they came in and stay trapped.
I was a bit skeptical about this one, but it does work: To get rid of gnats and other plant/soil small flying insects set a shallow pan (I used a pie tin) of Dawn (1/2 teaspoon) and water (1/8 cup) near where they are. I went back in 2 days to check. The water had evaporated and there were LOTS of dead bugs.
A mild hydrogen peroxide solution can help kill fungus gnat larvae without harming your plants. Mix one part 3% hydrogen peroxide with four parts water and pour it over the soil. This mixture will fizz as it attacks the larvae. Be sure to let the soil dry out afterward to prevent the gnats from returning.
Quick Fixes
Luckily, there are simple ways to get rid of gnats quickly:
HOMEMADE GNAT TRAPS
Using a solution of vinegar, wine, decaying fruit or beer placed in the bottom of a jar that has a paper cone placed over the top of the jar to prevent the trapped flies from escaping.
Coffee grounds as a natural method against fungus gnats is a popular and effective solution. The coffee grounds contain nitrogen, which inhibits the growth of fungus gnat larvae and kills them. Simply sprinkle some dry coffee grounds on the soil of the affected plants.
Fungus gnats lay their eggs within the first inch of soil, so removing and replacing the top inch or two of soil can help physically remove the fungus gnat eggs and larvae. Avoiding overwatering your plants and allowing your plants to dry out a little more between waterings can help keep fungus gnats at bay as well.
A 3% hydrogen peroxide solution is safe for nail application and effective against fungus. Avoid higher concentrations, as they may cause burns or skin irritation. Apply hydrogen peroxide directly to the nail with a cotton ball or swab, avoiding surrounding skin.
Mix half a cup of baking soda and half a cup of salt. Pour the mixture down your sink and shower drains followed by one cup of distilled white vinegar. After the mixture is done fizzing, flush away the dead gnats with water. Dish soap: Mix liquid dish soap in boiling water and pour it down the sink and shower drains.
This match made in heaven has been a household staple for a long time and I make sure to keep it handy. To make the solution is simple and easy on the wallet! Pour equal parts of vinegar and Dawn into a spray bottle. Gently shake, then spray liberally onto the surface to be cleaned.
Female fungus gnats lay their eggs on the surface of your soil or potting medium, but they may be underneath plant debris such as dead leaves. They hatch into larvae, which live within the soil.
Just add the liquid dish soap, set it out in the open, and wait for the gnats to dive in. Mash an overripe banana or two in a bowl and cover the top with plastic wrap. Secure the plastic wrap with a rubber band, then poke a couple small holes in the plastic with a toothpick or wooden skewer for the gnats.
Vinegar may attract gnats more than it kills, since it mimics the fermenting fruit that gnats love most. Vinegar traps might catch a few gnats, but they won't be enough to stop a full infestation on their own.
Similar to our bowl trap, we're going to want a sugary substance to attract the flies. You can use the aforementioned apple cider vinegar or wine, but you can also use beer, red wine vinegar, or even rotting fruit if you've got any lying around.
Topical treatment with Vicks VapoRub: The combination of camphor, eucalyptus oil, and menthol, the three main ingredients in Vicks VapoRub, is believed to stop the growth of certain fungi. Follow the same application process as for tea tree oil. Numerous readers swear by this.
Both rubbing alcohol and hydrogen peroxide kill fungi, too. Which product you use depends on what germs you're trying to kill, the surface you're trying to kill them on, and how much time you have. Rubbing alcohol works faster, but it can damage porous surfaces such as wood or granite.
Soaking your foot in peroxide can, in some cases, help get rid of toenail fungus. However, because it is difficult for hydrogen peroxide to reach all of the areas of the toe where the fungus can grow, such as under the nail, in the nail bed, it can be difficult to completely treat advanced fungus with peroxide alone.
Instuctions: Pour apple cider vinegar into the jar/bowl. Add water then add just one drop of mild liquid dish detergent. Set the mixture in the area where gnats are a problem. The gnats are naturally attracted to the vinegar and the drop of soap kills them.
Make the natural habitat inhospitable. This means drying out the soil they live in because fungus gnat larvae need moist soil. If you let it dry out completely before your next watering, it will get rid of the gnats in the soil and discourage new adults from laying their eggs.
Because fungus gnats thrive in moist conditions, especially where there is an abundance of decaying vegetation and fungi, avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings. Clean up standing water, and eliminate any plumbing or irrigation system leaks.
Instead of throwing spent coffee grounds in the trash, some homeowners leave piles or lines of coffee grounds around their gardens and homes to keep flies, mosquitoes, and other pests away. Coffee grounds are also often used to deter slugs and snails, reduce weeds without chemicals, and even repel neighborhood strays.
Coffee is fresh produce, and its enemies are oxygen, light, heat, and moisture.
They are usually found in saturated soil (like overwatered house plants) as they feed on decomposing matter - coffee grounds will serve that purpose if they are moist. If fungus gnats, they are harmless to you, children or animals but are quite annoying.