Ask Mr. Smarty Plants

We are assuming that you are referring to fungus gnats in dirt in your house plants. While they don't hurt anything, they are a nuisance indoors, and sometimes their larvae can damage roots and seeds in the soil. The life cycle of a gnat is that the adults deposit eggs on or in moist soil. Females lay eggs in soil containing decaying organic matter. The larvae feed on that material, and love moisture, and when they hatch, of course, more gnats!

The first step is to maintain good sanitation around your house plants. Remove any dead vegetation, fallen leaves and other debris from the base of the plant.  Next, replace the top few inches of soil with a sterile potting mix. Make sure your pot has good drainage, and that water does not stand in the soil. Don't water until the top 3" is dry-stick your finger in to check. Most indoor plant problems are due to the fact that it's just too easy to water them. Every time someone passes by, they think the plants could use a little drinkie. Not! Maintain good air circulation around the plants, ceiling fans, open windows when the weather allows, whatever will keep the air moving to discourage the fungus. 

The Lady Bird Johnson Wildflower Center recommends neither for nor against the use of pesticides, but if the above suggestions still don't cure the problem, there is a natural product called BTi (Bacillus thuringiensis) that can be found in products specifically for gnat control. Whatever product you use, be sure to read and follow directions carefully.