Experts and BHG readers answer.
clematis won't grow
"My first thought is that it's the clematis, and not you or your garden. There have been some newer introductions in the last few years that are far shorter than others, and there are some that are bushy, rather than climbing. I don't know the names of yours, but if you have the nametags, you might look them up on the Internet and see what you can find out.
Also, clematis need full sun, but they like shade around their feet to keep the roots cool. Planting shorter plants around their bases will help with that. "