Bake Soil to Pasteurize Before Germinating Seeds

January 25, 2016, by Ken Jorgustin


Make (Prepare) Your Own Soil To Germinate Seeds

A ‘do it yourself’ soil treatment for germinating seeds.

If you buy ‘special’ soil at the store for germinating seeds, it has most likely been through a pasteurizing process (not to be confused with sterilized).

You might wonder why it may help to germinate seeds in soil that has been through a pasteurization process… It’s because the process eliminates some of the organisms and spores that could harm your seedlings. The process will eliminate most diseases, weeds, insects, weed seeds, and fungi in the soil.

It is also safe practice to pasteurize regular potting soil bought from the store prior to planting seeds, although they do make special purpose potting mixes for germination.

The do-it-yourself procedure is pretty simple. Here’s how:


How To Pasteurize Soil For Seed Germination

Add soil to a baking pan
Cover the pan with aluminum foil
Bake at temperature between 140 and 180 degrees Fahrenheit
When internal soil temp reaches 140, continue at temp. for 30 minutes


Do Not Heat Above 180 Degrees F

For best results, do not let the temperature rise above 180 degrees Fahrenheit. Here’s why…

When soil is treated at 140 degrees Fahrenheit, most of the beneficial microorganisms survive. Their presence stops or slows the growth of plant diseases.

When soil is heated above 180 degrees Fahrenheit, this may cause a buildup of harmful substances in the soil and will kill all microorganisms (including the beneficial ones). This may cause diseases to spread very rapidly (with the absence of the beneficial natural enemies).

(Reference: Propagation Soil Preparation)



Preferably use moist soil (not dry, not soaking wet). If dry, add some water and mix it up. If wet, then let some evaporate out first. When the soil is squeezed in your palm, it should clump together somewhat.

Ideally, use a ‘meat thermometer’ due to its ideal temperature scale range. Poke a hole in the foil and insert thermometer until it is about in the middle of the soil depth. Be sure to use a thermometer that is oven safe if you’re going to leave it in there.
CDN Meat/Poultry Ovenproof Thermometer

You can also use a non-oven-safe thermometer by sliding out the oven tray and occasionally checking the internal temperature for 140 degrees.
Taylor Precision Instant Read Pocket Thermometer

Note: Be prepared for an unpleasant odor (My experience actually has not been too terribly bad)… Your experience will vary – depending on your soil. Definitely turn on the vent hood external fan if you have one!