Soil sterilization for indoor use, my new easy method

General Gardening
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Hello everyone,

I often start growing plants indoors during the dead of winter. While I don’t encounter issues every year, I sometimes deal with spider mites or other insects. I resolved this problem after I started sterilizing my soil. However, sterilizing large batches of soil and ensuring the right temperatures to kill insect eggs has historically been a challenge. I have tested oven cooking (expensive heating/cooling bills), boiling water (never hits appropriate temps unless doing very small batches), microwave (unevenly heats soil).

I wanted to share my newest—and easiest—method for sterilizing large batches of soil:

  • I use a large slow cooker or roaster (there are several affordable models that hold 4+ gallons of soil and cost around $60).
  • Add the preferred amount of soil and ensure it’s moist throughout.
  • Cover with the lid.
  • Set the temperature to 160-170°F and let it sit for several hours.
  • Use a thermometer to confirm that all parts of the soil have reached 160°F for at least 30 minutes.
  • Let it cool down, and you’re all done!

I personally use the 22-quart cooker by Aroma—it’s large, inexpensive, and has temperature controls—but plenty of other brands offer similar options. I also use pro-mix potting soil or other potting soils without composted materials as I would imagine theres an odor with heating.

I hope this helps someone!

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I wonder if a pressure cooker is overkill…

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I looked into pressure cooking as well, the issue I found was that they all go well above 200 degrees F, and toxic byproducts that are potentially harmful to plants/seedlings start forming at above boiling temps. They also tend to only come in smaller sizes.

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if I thought it was necessary I would go for steam barrel pasteurization. mushroom growers have this down pat.

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This is really good info to have. I was aware that a minimum temperature had to be reached, but a max temp was off my radar.

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I imagine mine has a setting for this; I know the yogurt setting is close.

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Let me know if you manage to pressure cook under 200 degrees. That would save lots of time as compared to this method.