don't do it like that, ashes are high-nitrogen, can hurt the plants, turns to lye, in fact ... use a propane torch to sterilize your soil outdoors, if you wish, most hardware stores sell a cheap 'spreader-nozzle' to fit the small tanks ... spread out your soil on a pan or something (concrete may 'pop' from the heat, wear eye protection) ... most quality potting soil is pre-sterilized, but that doesn't mean much, if it sits for awhile, bugs will infiltrate the bags, naturally ... :smokin: