I have tried various methods as well for fungus gnats; cinnamon, sand, chamomile tea and they didn't work. I never did try the dishsoap drench though. I don't know if you use chemicals or not, but what some hybridizers use in their greenhouses for fungus gnats and other pest is "Bayer Advanced Tree and Shrub"; Bill Waldrop and Larry Grace use it. It comes in liquid or granules; I have used the granules in my potted plants I bring in for the winter. You just sprinkle the recommended amount and water it in and it gets absorbed into plant. I've used it outdoors as well in my potted plants and seedlings. For me it works great.
