Firstly, don't clamp the trellis to the wall: plants need air circulation to help them to grow healthily, and a lot of mildew problems can be avoided if you put wooden blocks onto the wall first, then attach the trellis, so that it is at least an inch or two clear of the wall.
This also allows space for the stems to twine around it: this applies mostly to jasmine and honeysuckle, as personally, for roses, I never twine the stems around the support - instead, I always tie them to the support. I don't like seeing contorted rose stems, I would rather have them growing straight, so that I can more easily select the ones I want for my "framework of old wood" that we all strive for (along with "open goblet shaped" shrubs).
Here's a photo of a really good example:
As you can see, the Client here has attached study cross-struts to the walls, making them part of the overall design, then has simply screwed the panels to the cross-struts.
Five minutes with a screwdriver, and we can get the whole lot off for wall repainting, although in fact there is such a good gap that last time, the builder just ran his long-handled roller along behind it from each side!
The ultra-efficient way is to use hinges at the bottom of the trellis panels, with a swivelling peg or clamp at the top. Then, when you want to repaint the wall, you can unclip the top, and gently lean the trellis outwards, either to the ground, or to a whatever angle you need, instead of having to cut everything down to nothing.
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