@ QV: Didn't know much about it, looked some stuff up and yes.. Hibiscus is a sub-/tropical/Mediterranean genus of plants by large but I got the variant that can endure the fairly mild Winters in Holland. Wiki-link:
http://en.wikipedia.org/wiki/Hibiscus_syriacusNot sure about the level of influence the 'warm' Gulf Stream has here.
It's quite a bit less than let's say Western parts of Ireland or W. Scotland for sure. Here the North Sea tempers the more extreme cold temperatures and likewise the more extreme high Ts too. Predominant south/south-west/west wind directions are a factor of influence here too and blahiah....
Well, I also have a fig tree in the garden (on a sunny spot and a bit protected against (cold) wind) which kinda proves the rel. mild climate this corner of Holland has.