Someone in one of these forums said she put one of those mosquito dunks in her watering can & left it overnight. She then watered the plants with it.
She said it worked. I never tried it myself, but it's worth a shot.

If you have a container with just dirt & no plants, you can pour boiling water throughit.
That, I HAVE tried & it seemed to work for me.

BTi (that's what's in Mosquito Dunks) will definately kill the larvae of fungus gnats. You'll have to water with it several times. BTi is also available in liquid form, but is much harder to find in small quantities. Yellow sticky traps will help control the adults.

Agree with the above AND do try to get those sticky traps as noted by seeker11, so that you can get those adults too before they lay more eggs. I had to use sticky traps last year because they managed to get into the mulch of a few of my smaller pots. The traps work quite well.

A simpler method is to let your plants dry out completely in between watering. Fungus gnat larvae need a consistently moist environment to survive. Once the soil drys out completely, their history!

Harvestmaster

dryng out the soil a bit is a good idea. i read you can drench the soil with Gnatrol- it's a microbial pesticide containing a bacteria that kills the larvae. i'm personally not big on using chemical or pesticide but if the soil have fungus problem like that it'll be probably necessary to use them. otherwise they'll eventually die. i have plants that i lost like that.

I make a camomile tea infusion and use it to water the infested pot. It always works for me.

Lana

Yes, Gnatrol is very effective, and quite convenient to use. ("Gnatrol" is a brand name for BTi in a liquid form.) However, it's a bit difficult to find in small quantities; Mosquito Dunks also contain BTi and are easier to find. I'm including a link to the place where I buy Gnatrol, in case you decide to go that way. They also have yellow sticky traps, btw.

Here is a link that might be useful: Gnatrol source

I killed mine out of my Strawberry plants by using 1 Tablespoon of Listerine per gallon of water. Worked like a charm. (I also mixed it with Canola Oil and Dish Soap and sprayed it on the spider mites, haven't seen a spider mite since ha ha).

Best Wishes
Amino-X

I put a half inch of sand on top of topsoil.It suffocates them

Mosqito dunks left overnight in the watering can worked for me. But then I got some beneficial nematodes so I dont use the dunks now.

Beneficial Nematodes are the best thing ever for fungus gnat larvae.
Kills em before they eat your plants roots.
Chelsea Garden Center has 'em.

Thank everyone for all your helpful tips. Winter will be setting in soon, but at least you've all got me prepared for next spring.