I know that you can kills gnats with heat. Can you place a bag of potting mix in the deep freezer and kill the buggers?

I've wondered this many times.  I must know!  Someone knowledgeable reply!

Potting soil has fungus knats in it when you buy it ?

My hunch is that it might kill adults or larvae, however I don't know about eggs. I don't know their life cycle but I mean fungus gnats appear every year here where it gets below 0 degrees F during the winter.

Tried it. Does nothing. They can take up to -60F.

I believe freezing should kill the larvae and the eggs, as all cells should split once frozen. The only way to avoid this would be flash freezing with liquid nitrogen. I bought some potting soil and let it on the porch for the winter; when I recently brought it in for cuttings I noticed that there were no fungus gnats :). 

Apparently freezing doesn't kill them.

http://homeguides.sfgate.com/can-kill-fungus-gnats-freezing-dirt-72920.html

Here's the money quote:

"An Alaskan researcher discovered that the fungus gnat Exechia nugatoria is easily revived when frozen to minus 25 degrees Fahrenheit, and some members of the species may even come back when frozen to temperatures approaching minus 60 degrees. "

Here's more:

http://www.adn.com/article/20090530/scientist-finds-fungus-gnats-survive-winter-half-frozen

Weird! Them little tiny things can live to -60?!!!