Use hydro peroxide mixed in water when water your plants. Mix it at a 4 parts water to one part hydro peroxide. It will kill the gnats but continue to use the solution for at least two full weeks as the gnats lay eggs in the soil which are unnafected by the hydro peroxide. You have to kill off the whole life cycle to get rid of them. Also, the gnats will move to other plants in the area unless they are treated as well.

No, the hydro peroxide will not harm the plants. It will help with damping off fungus as well. I have heard it helps with root growth as well.

Make sure you use the 3% hydro peroxide that comes from the store. There are stronger versions but the 3% is the most common.

Good luck.

peroxide will work and is the cheapest method, but keep in mind it will likely kill any beneficial bacteria organisms in the soil. a better option would be to use neem oil extract as a soil drench.. about 1 tbsp per gal of water. the neem oil will also help condition the soil as a bonus as well.it won't kill the flying gnats, but it kills the source (the larvae/eggs inside the soil).

Mosquito Dunks, sold at most hardware stores. It takes about two weeks of soil drenching for the same reason that esox mentioned. You would crumble 1/2 a dunk into a pail of water, let it sit overnight to activate the bacteria, then thoroughly soak the potting soil. Let the Dunk crumbs stay in the soil so it can work all winter long.

Steve.

I bought some dunks yesterday and broke apart on top of soil. Adding extra to water pail right now. Hope that works. Going to do a gallon of apple cider vinegar trap as well lol.

Since you've added Dunk bacteria already, i would not use anything anti-bacterial at this point. The reason i let Dunks sit in the water pail overnight is so the bacteria can multiply and better distribute itself within the container upon watering (they hitch a ride with all of that water). If you are concerned with chlorine/chloramines in your water then you can stir in a few drops of lemon/lime juice beforehand to neutralize it.

Personally i would save the apple cider vinegar and just keep using the sticky pads to mop up some of the adults, though even that may not be necessary at this point.

Steve