Okay, Cricket, here I am to confuse the issue,
lol.
AHS Encyclopedia of Garden
plants...
The President (Clematis Group 2) Free flowering, early, large flowering climber bearing single, rich purple
flowers 4-6" across with silver undersides and red anthers in early summer.
Clematis Group 2 - bear
flowers in late
spring and early Summer on sideshoots arising from the previous year's growth, and in mid to late summer on the current year's growth. (There's more about leaves, etc.)
Going by this info, I'd suggest leaving pruning until after the first flush of bloom (which will come from the previous year's growth); then prune the stragglers and for shape when blooming slows down (because it should bloom again on the current year's growth). That way you get the best of both blooms.
I'd imagine you know that while clematis prefer full sun they do like their roots protected by a mulch or groundcover; that keeps the roots from drying out and overheating.
Hope this doesn't confuse the issue :rolleyes:
Barb,
zone 5