Apologies for re-stirring an old thread; was just skimming through and saw that the OP lives where I do, and im currently digging into M S Smiths writing. His 'Northern Climate Cacti Guide' is really nice and in depth, especially his flickr account (soo many beautiful beautiful cacti ).

This is an old comment but I just wanted to say that I know from experience San Pedro does not do well in freezing temperatures. I posted in a different thread about how I accidentally killed my biggest Pedro by leaving it outside overnight last winter. It was a sad day. Basically, you don't want them outside once frost starts appearing or you're gonna have a bad time.

To the above, thanks for the info! I'll have to look into this stuff since I live in a cold climate as well. Although we are having a mild winter I am excited because last winter was really cold!

Where I live in Seattle it seems to work best if you bring them in somewhere for the winter and let them go totally dormant - cold and dark and dry. A little freezing seems fine, but I think they need the dark to really go dormant and it seems to work better then trying to give them light in the winter here.... Dry is obviously very important. Some people I know put them back in closets or in the garage.

It is natural for cacti to get light all year round - in winter their growth slows but they do not become dormant - last year´s growth will be ripening and hardening in preparation for next year´s season. I give my plants natural light all year round - when I grew in Scotland they lived in a greenhouse heated by a paraffin heater to keep them above freezing, but they were kept totally dry for several months.
Here my climate is frost free and they live outside March to November - December to Feb they live in a cold frame to make sure they stay dry. But they are never dormant - last week I got my first flower of 2016 - my Stenocactus multicostatus.

Thanks for your input. I have kept my cacti by a window all winter and they seem to be doing well. And congratulations on the first flower of the year! I hope my pedros will flower sometime soon. That would be nice.