Answer: Roses can be tied to the trellis to hold the canes flat against it. Tie with a soft supple material in a figure eight pattern, one loop around the cane and one around the trellis. It should be somewhat loose so it won't damage the cane. You can also weave the new growth through the trellis while it is still supple. Which method to use depends on how you need to protect the rose in winter. If it is a variety that needs to be taken down and placed along the ground with insulating mulch, you have to tie it so it can be removed easily, or the entire trellis will have to be taken off the wall.
Clematis may need a stick to climb up until they reach the bottom of the trellis, then they make their own way through it and upward. (Just take a stick or small stake and lean it from near the base of the plant to the bottom of the trellis.) Clematis grow much faster after they have been in the ground for a year or two so will not need much help.
I hope this helps.
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