http://www.gardeners.com/Gnat-Guard/GardenPests_Insects,34-299,default,cp.html

It is perishable so can only be used to treat for a short time, pricey to keep buying as you add plants. I like mosquito dunks for fungus gnats.

Hi Brent
Do you just float the mosquito dunk in the water that your using to water your plants?
Vito

Yes, just toss a whole or half of one in your watering can. It will take a week or more for the gnats to all be gone, the dunks are made with BTi, a soil bacteria, and only kill the grubs.

I haven't heard of or used mosquito dunks before but I'm definitely having problems with fungus gnats.  Are these the mosquito dunks you refer to?  If so that could be a great solution.  I've been using little saucers of apple cider vinegar to catch them but it's not getting to the root of the problem.

Thank you Brent.
I used them last year, just wondering if I used them correctly.
Vito

Those are them Tim, that is a lifetime supply for this purpose, one dunk can treat well over 50 gallons of water. The active Ingredient is Bacillius thurigensis var. israelli, or something like that. It is also the active, alive!, ingredient in Gnatrol. Cost is about the same but I think you get more with the dunks and there are smaller packs of dunks available. Gnatrol says its shelflife is two years, I think dunks would stay good for about that long too.

A little liquid soap in the water you are using to water with kills the larvae in the soil. My family has used this method for many years and it works.