Posted: 12/02/2016 at 19:07
That's fine general advice Richard but these are less than a year old plants and I disagree with you in this instance and follow the RHS advice which says that all year old clematis, regardless of type, should be cut back to encourage more stems to shoot from the root crown. The following is quoted from their 'Group 2' advice page:
"Unless the plant already has three or four healthy stems growing from the base, all newly planted clematis should be pruned back hard the first spring after planting. Cut back to just above a strong pair of leaf buds about 30cm (1ft) above soil level. This will encourage multiple stems which can be trained in to supports to give a good coverage."
I've been following that advice for years with excellent results.