I may start with a pasteurized potting mix, but stuff I add to it, like sand, grit, compost, etc. is not. Nor are my pots bleached or even cleaned well. I really don't understand all the fuss when you are not dealing with micropropagation techniques, or finicky seeds. I stick to the "all organisms work in unison, good and bad" principle.
Not that this is the only right way to do it, but it's the way I do it.
Rick Rodich zone 4a. Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA
My process is much like Rick's... the base is potting soil but it's very heavily amended with sand, grit, and perlite. As I plant things out, I dump excess soil from the pots into a bin and then I reuse it the next winter. I never, ever wash pots. Seems to work OK - damping off is not a problem.
It sounds like coral sand would be pretty expensive if you need more than a little (given how such things are priced in the aquarium/pet trade). I take it you are looking to create a calcareous soil? If so, would it be possible to get that limestone grit that's intended to be fed to chickens (to provide CaCO3 for their egg laying)?
Calgary, Alberta, Canada - Zone 3
-30 C to +30 C (rarely!); elevation ~1130m; annual precipitation ~40 cm
Thank you, Lori, Rick for the information and suggestions. Will go out shopping for poultry grit tomorrow. (I hate it when I buy an "alpine" plant and find it potted in commercial mix, and it so difficult to try to remove from the roots)Charles Swanson MA USA
NE Massachusetts (New England) USA zone 6 (5B to 6B)
gardens visited, photographs: www.flickr.com/photos/wildmeadow