Kill Fungus Gnats In Garden

Fungus Gnats like to lay their eggs on moist soil with many organic matters. To keep surface soil dry, I exposed them to the sun and try bottom watering.

Observation: the soil might is still wet with bottom watering, unless I stop watering. This might stop gnats from laying eggs, but it has no effects on little gnats already in the pot.

I spray some neem oil on the soil, where the gnats would fly away or jump around (the small ones can't fly). It does kill some of them. For it to be effective, you need to spray a large amount or drench the soil, which might be too costly if you buy commercial neem pesticides.

Use fungus gnat traps with apple vinigar (or white vinigar with sugar), and add it a few drops to dish liquid to reduce water tention. Pour the liquid on a shallow and wide area container.

The trap is not very effective, only trapping a few gnats per day (where yellow sticky paper can trap up to 100 per day).

Pour Mosquito BTI solution into the soil to kill the baby and larva gnats within 24 hours. Mix 0.02g of Mosquito BTI per litre of water.

Drench the pot soil with Hydrogen Peroxide <1% (mix 4 part water with Hydrogen Peroxide 3%).

So tiny gnats will try to jump around to escape. You can spray them with Hydrogen Peroxide or Home-made Neem Oil Pesticides.

The downsides of using Hydrogen Peroxide is killing all the microbes in the soil (both good and bad).

Hydrogen Peroxide helps with root rot (caused by fungi and bacteria in the soil, also caused by excessive moisture in the soil due to overwatering), by killing fungi and bacteria in the soil and restore oxygen. The extra oxygen also help the roots to absorb more nutrient.

I add mulch on top of the soil to discourage gnats to continue to lay eggs.