It's been below freezing here in NW Cascadia for a long time, and in the teens most nights in my microclimate. I still have the pump running in my trough pond, with a 250w heater. When the splash-ice melts enough to see the fish, they still look fine, but my plants are probably toast.
Winters are crazy here. You never know if it will be 50's and monsoons the whole time, or blizzard noreasters coming out of the Fraser river valley. Sometimes you get all of the above in just a few weeks.
I've managed to overwinter some fall lettuce by winding some old christmas lights around the plants, then adding some weighted row cover. We get such terrible winds here that I had to take in the greenhouse plastic i tossed over that, but those plants are still trying. If they survive I'm going to save seeds from them.
We're planning to convert a stable with good southern exposure into a winter house for plants and such. The building has stood up to winds for a long time, so putting a row of salvaged windows in the south wall should get enough winter light without having to run out and nail things down when the winds get going.
