Why do you think this is Clematis montana? Does it have the same foliage?

Is this blooming now or is the picture from last spring?

This is what they told me they bought last year but they can't find the tag. This picture was taken last week and the flowers have opened up even more now. I have to tell you that they are not conscientious gardeners so I'm sure this plant has had to look after itself most of the time.

Probably C. terniflora or similar.

Yes, I seriously doubt it is a montana.........first, I have never encountered a 'dwarf' montana - they get to be massive vines. Second, while they can throw a few flowers in late summer or fall, they would never have a second bloom period as intense as that shown in photo. And white montanas are not at all that common and tend to be somewhat hard to find - most cultivars are in various shades of pink.

Could be C. terniflora - an appropriate bloom time for that species as well as similar appearance. But a second bloom cycle?? Very unlikely. And if SAC, it too is no dwarf - it can get as large - if not larger - than any of the montanas. 25-30 feet is pretty standard.

One my girlfriend had for years on Camano Island never got very big, maybe 10' or so at one point.