Best Growing Medium For Potatos

I'm doing potatoes in bags this year.
Since I will be choosing the growing medium, what would they like best?

If I was buying grow media for potato bags... which I never have. I would probably do something like 1 part sand, 1 part peat, and .5 parts well rotted but still with some carboniferous woody bits swimming with mycorhizia type compost. Something like that would sound good to me.

Oh, and probably a couple ounces of Lime to go with that peat.

Thanks for your reply!
Sounds easy and cheap, no manure, huh?

No, but keep in mind I'm shooting from the hip!