I like to use a soil-less mix:

4 parts peat moss

2 parts perlite

1 part vermiculite

It's clean, light weight and has good drainage.

holzinger, do you add other nutrition or fertilizers? I'm curious about how your plants do in your potting medium.

They do just fine in that medium. I complete fertilizer a couple of times a year, but most of my plants don't stay in the pot that long, they get planted in the ground. Growing in this medium the average passiflora will go from seedling to plantable in less than a year.