Growing mushroom casing and spawn question
 

I am new to the whole growing mushroom deal
I am interested in growing shittake mushrooms
2 questions:

1)Other than buying spores or mycelium from a supplier could
I just buy some edible shittakies in the grocery store and use their
spores or mycellium?

2) What is the best/easiest/safest casing to use for shittake
Can i just simply use sawdust or is it an absolute must to use some
other type of casing if my spawn substrate is rye grain? (is that a good substrate to use for shittake?)

Thanks,
Matt