I live in Norway, and we have really cold winters. The engine still starts, you might have some other issues if you got a problem starting in winter.
(Even though i sometimes have problem with my starter, which is why i got a direct wire to it. But that problem for me, can come in summer time, as well. And the engine still starts both in winter and summer. Even though my idle is really low like around 600. (goes automaticly to around 1100 in wintertime.)