Here's a quote from Dirr (The Reference Manual of Woody Plant Propagation) on clematis:
"Most of the large-flowered hybrids are grown from single node cuttings collected when the tight flower buds are developing. Cut just above a node and shorten internode to 1 to 2" in length. ...Two node cuttings are also used to insure that buds will break and grow after rootings. Semi-hardwood cuttings can also be used later in the season for the easier-to-root types."
He recommends using rooting powder (@ 8000 ppm IBA-talc to be precise, but really, who's going to be that specific propagating a few clems at home. The manual is written with prof. growers in mind.) Expect a success rate of 60 to 70% in 4 to 5 weeks.
