Bugs in potting soil and their eggs are best controlled before using the soil. Sterilizing the soil in an oven is the best method for killing off the small pests. While you can use a microwave oven, the most effective heating method is using a conventional oven. Large amounts of potting soil can be placed in large, heat-resistant pans. When complete, the potting soil is free of insects, eggs and weed seeds.
Layer the potting soil in a shallow, oven-rated pan no more than 4 inches deep.
Cover the pan tightly with a single layer of aluminum foil. Seal the edges of the foil to the sides of the pan.
Insert the oven thermometer deep into the soil through the aluminum foil in the center of the pan.
Set the oven to between 180 and 200 degrees Fahrenheit.
Heat the soil for 30 minutes once the thermometer has reached 180 degrees.
Turn the oven off. Allow the soil to cool. Remove the pan from the oven. Use the soil immediately or keep it covered to use later. The aluminum foil cover will keep out insects from the sterilized soil.