Is your climate warm enough for them?

Here is a good page on how to start the seeds:
esp. the scarification process, if you are buying the seed.

http://blog.chestnutherbs.com/passionflower-from-seed-to-fruit-and-back-again

I will not be able to keep them outside all year, as I'm only in zone 4, but I don't mind wintering them indoors

The scarification info in your link was helpful, I've never done that before but will be giving it a go tomorrow! Thanks for the link!

Sometimes you can put seeds in a clear glass, in water, draining every day, until you see the beginnings of a sprout.
Then plant sprout side down.

mine can grow on. There is a wild patch and I think I could create a nice garden statement with them. I just have to get to them before the vine everywhere. I tried in zone 10 and they wouldn't grow for me at all. I don't know what zone 4 will get you, but they love zone 7.