Potting Mix for begonias

Ok, I hate to ask so many newbie questions but I did look back through the begonia topics for a couple of years and didn't see this discussed. What kind of potting mix is best for begonias? I know it should be well draining. Does it vary by variety i.e. Cane, or Rex ? Is a bagged mix ok or are people mixing up their own blend?

Here are some recipes used by Sacramento ABS branch members

http://begoniaweb.com/images/soil_recipes_sac_ABS.jpg

And some notes I took at the LA convention and typed up
http://begoniaweb.com/begonia_recipe_notes.html

I use a modified version of 'Joan's', omitting some of the ingredients like 'oak leaf mold' because it's hard to find commercially.

I think you have to experiment to find what works best for your growing environment, but I would agree with you that well draining is key.
Cheers,
Lali

Thanks for your post Lali, it gives me some options to try.