How wide are the bars of the trellis? It may need more narrow things to wind around. You could always use some ties to help it start up the trellis.

I use the plastic coated garden fencing, adding it to the back of wood trellis that are too thick. Works great.

Clematis newbie here, but I have been stringing vines for years with clear fishing line. I used the little wood trellis that came with the plant and weaved a fan pattern to the privacy fence behind the plant. They love the fishing line and even better, it's nearly invisible and makes the plant look like it's floating. Of course, you have to use caution for pets, kids, and adults not paying attention.

What type of clematis do you have? Does your clematis have leaf tendrils?
I have a Clematis âÂÂDurandiiâ which does not have tendrils and does not cling to trellises......
This vine is used to weep over a support naturally without tangling.....

Use the many available netting products or make your own with twine, rope, fishing line, etc

You already have the framework so just add those lines to the framework.

An alternative is that while the plant may not support itself right now, you can just tie it up to your current support. That will get it off the ground and upright. Going forward, try to support any new growth in this way also.

I have found that the netting products need to have a good sized square or the vine doesn't cling well and netting tears when I remove the vine. Twines and other strings and ropes work well. The advantage of gardening fencing is it doesn't have to be replaced. Try different approaches and see what works for you.

Great suggestions! My clematis does have tendrils, but as others mentioned, the wood trellis is too thick for the tendrils to weave around. I'm going to try thick fishing line, which seems a pretty simple solution. The garden netting I've used in the past tears when pulling off the dead vines in the spring, as someone mentioned.

I'm happy to finally know what the problem is--makes it much easier to solve!

I'm done with netting, the squares are too small and it does tear.

The metal grids they sell at building/home improvement stores to reinforce concrete are cheap and perfect. Ditto cattle panels at farm/ranch stores.

They also climb rebar easily

I promise, once you use fishing line, you won't reach for anything else.

I also have purchased pretty trellises only to learn that there are not enough places for the delicate clematis to grab and climb. Perhaps others have also paired clematis with roses on rose obelisks only to have the rose fail to grow fast enough to provide support? I solved both problems by using inexpensive small trellises that are sold to be used in big pots or for short vines. I attach them with clips or wire to the obelisk rings. I also found a few low decorative fence sections that are sold to stick in the ground and hold up plants along a path. They are black like the trellis with a scroll design. By turning them this way or that and wiring them in place you would swear that they were part of the original. So, look around. I do not have a hubby to cut heavy wire etc. so need to be creative. I find these things at the big box stores and the dollar store.

I tie with twine a few major starts to the inexpensive fan type trellis's. The others grab onto each other,etc and they present a mass in a natural fashion. on the brick house I have lathe piece which I also tied some of the rear pieces of the vines to and then the front tendrils follow or grow however. Upon clean up, I whack them off 12" from the ground, untie the back pieces and carry my bale of climatis out neatly to dispose.
Kerrys; I would suggest after enjoying your blooms -whack it back and tie some of the trimmed bad boys to whatever structure you use. It will look nice and neat and It will probably bloom again this summer, I do this with JackM. don't know which one you grow.

Looks great johnny!