Dorset,
United Kingdom 
Die back on a climbing hydrangea. I cut the offending branches back last summer but it is not responding. Half the plant seems healthy and the other withered. Does anyone have an answer? Thank you in advance.
12 Jun, 2014
Wait until flowering is over and then cut out the affected branch(es) - use that as this year's pruning.
If you need to check its size then prune out about 1/4 (1/3 at most) in spring.
12 Jun, 2014