I eat yogurt for breakfast every morning so I generate a lot of yogurt cups. I use them for both seed starting and rooting cuttings.
My current dilemma is that I've switched to Greek yogurt, same size container (6 oz) but wider, more shallow cups. I don't like those cups as well for my plants so I need to find a different brand of Greek yogurt with cups shaped so that my plants will like them.
No fancy homemade potting mixes here. I just use a good professional mix, usually ProMix, for everything. If I want faster drainage, I just add a little perlite.
Karen