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How to Sterilize Composting Soil

If you are thinking of bringing your yard plants into the house at the end of summer, you'll probably want to do something to make sure you are not bringing bugs or harmful bacteria in with them. Sterilizing the composting soil before you transplant your non-hardy plants will ensure that any little bugs or their eggs will be killed before they enter your house. It will also kill off any weed seeds that might sprout up unexpectedly. Use the sterilized soil as you would regular potting soil for indoor plants.

Mound a pile of the composting soil you want to sterilize on a metal baking sheet or pan. You can make it as high as you like, just not so high that it will spill over into your oven. The thicker the pile is, the longer it will take to sterilize.

Turn on your oven to 350 degrees. Place the tray filled with composting soil into the ovenon the center rack. Allow the soil to heat up until it reaches an internal temperature of 140 degrees--about 10 to 20 minutes, depending on the thickness of your pile. At this point, any little critters or eggs will be killed. Keep it at the 140 degree mark for at least 10 minutes and then remove it from the oven.

Allow the composted soil to cool to room temperature before attempting to use it for your plants. You can stir it to help aerate it and cool it down a little more. Hot soil will kill a plant almost immediately, so be patient and wait for it to cool down.

Sterilize Used Potting Soil

Remove any plant material, including old roots, from the potting soil. Fill an old baking pan or metal container with a 2- to 4-inch layer of soil. Puncture a small hole in the center of the aluminum foil. Set your over to slightly below 200 degrees Fahrenheit. Place the pan in the oven. Monitor the temperature closely and do not allow it to go over 200 degrees as this may damage your soil. Colorado State University explains that high temperatures may cause toxins to form in the soil. This prevents contamination of the sterilized soil with pathogens as you repot your plants.


It is not recommended to do this for outside plants as there are beneficial microbes that are killed off during the heating process.

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