Hydrangea seemannii is pretty OK to -8/9c which is the lowest I can vauch for, never seen damage, bearing in mind it is happiest in shelter from wind a wall or large tree trunk helps with frost protection anyway. mine is covering the walls and roof of our outside loo.
Re weddings, I only have the one daughter so had no previous experience, pretty much left it to her to decide what she wanted, but 100 people takes a bit of looking after and the two days before and two days after were pretty manic as we did everything ourselves (if you can afford to let someone do it all so you can walk away after thats the way to go!)
So my only regret is she took so long to get around to it as 10 years ago it would not have been so tiring!
Anyway it went very well, we all had a good time, and even her mad bonkers idea that our dog would be the Best Man and ring bearer worked, (I had been expecting to recoup some money from "You've been framed") The dog had to lead the 5 little children attached to him by ribbons down a steep set of granite steps, across the lawn then across a narrow bridge over a large pond to the island where the actual wedding was to take place, all this with no dry run or practice!
hydrangea seemannii 001 by charliepridham, on Flickr
hydrangea seemannii 003 by charliepridham, on Flickr
hydrangea seemannii 002 by charliepridham, on Flickr