William, Thank you so much for these answers and the link to solarization of soil. I have told that bleach was good enough, but I doubted that. The articles and the link are my guides and thanks again.
NO BLEACH & Should not sterilize it at all you'll kill all the beneficial microbes that soil/plants need to be healthy. If think you must do something just spread it out on black plastic and let it set in direct sun for a few days,turning it every so often so it all gets a good equal dose of UV rays. If it has bugs(fungus gnats) or most fungal problems this will help too. you can add Beneficial organisms to soil to help it they are called Nematodes I buy mine at Arbico Organics
Why would you bother, at all? Plenty of good potting soils on the market.
Have you bought any GOOD potting soil lately? Please tell me where you bought it. Mostly it's chunks of half-rotted mulch now.
I'm from Sydney (Australia) and I always buy potting mix that has a (rotting) compost mix or with the addition of other soil enhancing elements. Never buy cheap potting mix, as it quite often contains, as you have discovered, anything from ash, to things that can be toxic to animals - especially dogs. So it's always worthwhile to pay the extra $'s. Have you got your own compost area, or a compost tumbling bin for your kitchen fruit and vegetable scraps (never meat which will attract maggots, or bread/pastry which will attract weevils)? You can also add things like garden leaves and other garden detritus. A turning compost bin is best (saves you digging and your back), as you can add to it daily, and just turn the handle. You should also be able to buy 'garden worms' from your local nursery etc., which is a great addition for the compost, as they will aerate the compost (they also aerate the soil). Never add kitchen waste directly to the pots or garden beds, as it will attract rats.