
If you want to reuse growing media or to blend your own using finely screened compost or garden soil, it is best to kill any harmful fungi, bacteria, nematodes, or weed seeds that might be present. A microwave is not the best choice as they tend to heat unevenly, and some areas can overheat, which can be a problem.
An oven is the best technique. However, overheated media or soil in an oven can leave some “earthy” odors. A temperature of 140 degrees for half an hour is enough to kill most fungi, while most harmful bacteria and insects may require 160 degrees, and weed seeds 180 degrees.

An alternative option is to place the media in a large plastic bag made for oven baking, such as a turkey bag. Make a hole or small slit in the bag for air to escape and for inserting the thermometer.

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