Pasteurizing Growing Media or Garden Soil in An Oven

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 area can overheat, which can be a problem.

An oven is the best technique, however overheating media or soil in an oven can leave some “earthy” odors. A temperature of 140 degrees for a half hour is enough to kill most fungi, while most harmful bacteria and insects may require 160 degrees and weed seeds 180 degrees.

Foil Covered Pan

1. 1. Preheat oven to the target temperature.
   2. Place premoistened (not soggy wet) media or finely broken up garden soil in a large pan up to 4” deep.
   3. Cover pan and soil with aluminum foil.
   4. Place pan in oven away from heating element and check the temperature of the media or soil periodically with a meat or candy thermometer placed through a hole in the foil.
   5. When the temperature of the media or soil reaches the target temperature. Leave it in the oven for 30 minutes longer before removing it to cool.

Oven Bag

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.