One should try to top soil with compost and castings and water less. This is the most organic way to clear them. However, if after a week the problem does not clear up, there other methods to try. Here is a great site that has almost every organic method available to eliminating the gnats. http://www.smallfootprintfamily.com/controlling-fungus-gnats-organically...good luck, these little bastards will eat your roots if you dont take care of it.