Timing Autumn is an excellent time to treat soil. Disease-causing organisms and other pests are most active under these conditions. Many pests in cold, dry soils are dormant and thus very resistant to heat. Selecting the method Dry heat, steam, and aerated steam may be used to pasteurize soil for any crop. Usually most, but not all, organisms are killed.
Soil thus treated is said to be pasteurized.
Effective pasteurization occurs when steam or dry heat is used to raise and maintain the temperature of the entire soil mass to between 180 and 200 F for 30 minutes. Almost all living organisms in the soil are killed by this treatment. If aerated steam is used, the temperature of the entire soil mass is kept between 145 and 160 F for 30 minutes. Prevent recontamination Tools and equipment used to handle the potting mix and all surfaces that the mix will touch, including potting benches and dibble boards, must be clean so that the soil is not contaminated with disease-causing organisms. Cleaning is the first step, followed by disinfestation by heat or by chemicals.