Fungus Knats

Is there any problem using this solution: "Adding a tablespoon of natural apple cider vinegar to each gallon of irrigation water will also help keep plants healthy and control pests like fungus gnats."

The same article suggested a 'neem oil drench'. I have neem oil, but by drench does it mean submerging the pot/soil?

The problem isn't big at the moment, but my mid winter there was a quite an infestation. Reducing watering is a problem because the house is so dry.

Thanks

Not all your bonsai will appreciate vinegar, especially your buttonwood. It may react with chemicals in the soil to produce toxic acetates. Neem oil will probably do nothing. The single most effective way to reduce fungus gnats is to reduce the organic component in your soil. Never use peat moss.
Iris

By drench they mean mix your Neem oil to the manufacturers recommendations then water it into the soil until you see it come out the bottom holes, do this a few times till your soil is good and drenched. Will it work? I have read that Neem drenches can help with larva in the roots with regards to vine weevils. Fungus Gnats have a larval stage that is in the soil and eats your root tips. Try it out see if it helps

Another trick I have use is to cover the soil surface with a good inch or two of inorganic substrate, turface or the like, this discourages the adults from feeding at the soil level. They don't want to eat turface!

Ultimately its a sign of over watering, let the surface of your soil get good and dry. Vinegar is used to help lower ph in bonsai soils that are repeatedly subjected to hard water, its done ONCE a month, I doubt it would have an effect on Gnat larva, particularly at that low concentration.

Let your soil dry out then give the Neem a try and let us know how it worked.
Good luck... I HATE fungus gnats and am happy to help anyone in their battle with these beasts.
-Jay
Ps the automatic spell checker converted Neem to Enema, good thing I proof read, it made me chuckle.

Chemicals should not be needed. Fungus Gnats occur when soil is too wet and stays too wet. Improved soil and a better watering regime will get rid of all of them.

By drench they mean mix your Natures neem oil to the companies suggestions then water it into the ground until you see it come out the end slots, do this a few periods until your ground is excellent and soaked.