Clematis outer skin splitting.
Hi, I have various clematis plants which are all suffering the same problem which does not seem to conform to the various help pages. The stems appear to split their outer skins exposing the inner layer, and this in turn causes the stem to die. I have pruned off the affected branches but this does not stop the progress of the splitting. I have given a clematis feed every two weeks during the season and ensured the plants are well watered. The problem started early summer and continues now in early winter. Can anybody suggest what the problem might be