HiWould clematis grow in pot up my trellis rather rhan in the groundMany thanksSteve

If you can keep the pot well shaded yes, Clematis like to have cool roots.

And choose a smaller variety of clematis, with a pot that's at least 18 inches deep, preferably 2 feet, and 12 inches across.

As a rule of thumb, multiply the width of the area you want to cover by the height you want to cover it to, and divide it by 20, to get the height and width of the pot needed.