The Q&A Archives: Pasteurizing Soil

Question: The old soil from pots or trays, etc. is pasteurized with an automatic soil pasteurizer. This is my understanding of the process, the soil is heated and steamed to kill of bacteria and other undesired organisms. I do not know what temperature the soil will achieve under these conditions. How do I figure out what temperature the soil will achieve without the availability of a manual (ancient equipment), what essential organic material is lost in the process, and if a substantial amount of desired nutrients are lost, what additives would you suggest?

Answer: I hope we're talking about regular garden soil and not commercial potting mix. To kill harmful bacteria, soil needs to reach 180F to 200F for a period of 30 minutes. A higher temperature, or a longer period of time will kill the benefcial organisms in the soil. You can use a regular oven thermometer to check the temperature of the soil during the process. Without an automatic soil pasteurizer, you can still pasteurize soil by placing it in a clean and sanitized baking tray or pan. (use 1 part bleach to 9 parts water to rinse the tray or pan before putting your soil in.) Then add moistened soil and a baking potato. Cover the pan with aluminum foil and stick a candy or oven thermometer into the soil through the foil. Check the temperature and start timing when it reaches 180-200 degrees. The soil will be pasteurized when the potato is done. Remove from the oven and allow to cool before handling the soi.! (Don't forget to toss out the potato!)

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