Clematis armandii "Apple Blossom"
 

In February I purchased a Clematis armandii. I live in the North
East of England and have planted this plant on a south facing wall.

The two main stems have grown very well and have put on about 24-30 inches.
However, all of the new leaves have withered away. I do not think that this
is Clematis Wilt as the growing tips are
still growing healthily. There are 2 other buds which appear to have started
to grow but are not making any progress.

Could this be caused by cold spells of weather or could there be some other
cause? Should I prune these shoots back? If so when is the best time to do
it?

I would be grateful for any advice.

Many thanks.

Les