Easy Potting Soil Sterilization

January 20th, 2009 by david laferney Leave a reply »

I usually don’t worry about sterilizing compost or home made potting soil. However, this year I’m starting most of my plants under lights in a rather cool grow room – a fairly substantial investment of effort and time – and I just don’t want to take any chances.

If I had planned ahead I would have done solar pasturization by putting saran wrap on the top of a picnic cooler full of compost.  Since I didn’t plan ahead I did this instead:

Grilled dirt anyone?  The oven bag makes it look kinda like a dirt haggis.

Grilled dirt anyone? The oven bag makes it look kinda like a dirt haggis.

An oven bag full of  my best screened compost cooked well done on the gas grill.  I added about a quart of water so that it would all steam evenly, and punched a small hole in the top to keep it from building pressure – took about 2 1/2 hours to reach 170 degrees Fahrenheit.  The probe thermometer lets you be more efficient by not opening the lid.  Needless to say plan on just letting it sit there for several hours to cool.

If you only cook the compost you should be able to make 2-3 times this volume of sterile homemade organic potting soil by the time you add the other ingredients.

The oven bag looks no worse for wear and tear, and I don’t see why you couldn’t reuse it again – for dirt of course.  Next time though maybe I’ll do better and use sunshine instead of fossil fuel, but in the middle of January this worked pretty well without cooking dirt in the kitchen.


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