The title says what I do, but I have a couple of questions.
The first question is what to plant. I have two varieties of lettuce that have the reputation of doing well for winter (outdoor) gardens: Winter Density, and North Pole. I also planted Winter Bloomsdale spinach. I have one kind of broccoli in the ground. Cilantro is another that does very well in winter that I am planting both inside and outside the greenhouse. Is there anything else you think might do well?

The second question is the real motivation for this post. On the coldest nights, when it gets well below freezing should I have my greenhouse fan going all night long or intermittently, 1/2 hour on and 1/2 hour off. It needs to be on some because without a fan the coldest air will settle closest to the ground and will attack my plants, but having the fan on all the time makes the inside air hit the plastic more which will exchange the heat between inside and outside faster which will result in a lower overall greenhouse temperature.