How do I "train" Clematis to grow up a trellis?

You don't need to. It is self clinging. All you need is a bamboo cane pointing it up to the trellis to start it on its way.

How do I "train" Clematis to grow up a trellis?
Take the little vines and start wrapping them around the lower rungs of the trellis. If necessary, take a tie wrap to attach them to the trellis.
Reply:I use string that I hang from the trellis to the clematis. The feelers will wrap around and then grow up the trellis. Good luck!
Reply:Use a stick and when it gets tall enough then tack it to the pole with wire or something you can tie around it.