How do you thicken up vines?

I've been having a bit of trouble thickening up the branches on my Virginia creeper plants. I've let them grow all year year. Some of them are over 15 feet long but still maybe 1/8th of an inch thick. Is there a better way of achieving thickness in the branches of vines and other climbers?

First, you only dig up old, large plants. Then you prune, prune, prune. If you let them grow long, that's what they'll do. Period.

JimLewis wrote:First, you only dig up old, large plants.  Then you prune, prune, prune.  If you let them grow long, that's what they'll do.  Period.

Thanks. I have a very large creeper vine as well as a few small ones. I don't want the trunks of the small ones to get bigger, I just want the branches to thicken enough to where they fit the trunk. I'll definitely give your advice a try.