United Kingdom 
I had a lovely Montana clematis in a pot growing profusely over a gazebo & rose arch. Unfortunately it required moving slightly when the gazebo was replaced. it had burst its pot and was growing into the ground. The builder could not move it so chopped off the root appearing from the bottom of the pot. I repotted the root ball into a much larger pot and watered well but the foliage now looks very sick! Has it been killed or is there a hope it might recover? Your advice would be welcomed.
3 Sep, 2021
Answers
Thank you for your advice. i shall try to save it but will also buy a new one.
3 Sep, 2021
I would cut the top growth down to about 2ft so the roots that were left in the pot will be able to cope with the water demand. Don't over water, keep the compost barely damp, at this stage as the new root hairs will grow 'better' if they have to search for water and then the plant will recover quicker.
Don't give up on it until mid May and if there is no growth then it has died.
3 Sep, 2021
Thank you for the advice - that is most helpful. ! will do as you advise and won't give up hope until next year.
4 Sep, 2021
Previous question
We once tried to move a montana but it also died. You might try pruning it hard back and waiting for Spring on the chance that it might resprout. But Montana is very vigorous for an arch of that kind - it can get very massive and heavy. If it doesn't recover next SpringI'd suggest replacing it with another less vigorous variety more suited to the size of the arch. There are so many beauties to choose from. The "accident " may have done you a favour in the long run...
3 Sep, 2021