I built the greenhouse 20 years ago to grow plants in flats. Essentially a "sunshed," it is 9' by 20' and has a natural gas furnace but heat is only turned on for a few weeks each spring. The north wall and roof are insulated and the sloping south wall is covered with UV-resistant plastic film. A central bench, 18' long, takes up most of the growing space and I pull that out in October. Here is the bench after I had rebuilt it in 2013: After pulling this out, I was able to plant mostly Asian greens that I started near the end of September: Here they are on 20 October: Many of those extra plants waaay down there in the flat went into a narrow bed directly against the south wall. It fairly cold there and we'll see how they will do this winter. Here are some of the plants in the central, larger bed by 20 November: This bed with these plants has a low plastic tunnel over pvc hoops. That cover went over them after the 20th when overnight outdoor temperatures fell into the teens.
Our average temperature rose above the 20's yesterday so I pulled the low tunnel off the greens in the greenhouse.
The greens have suffered some from the low light conditions and there was even less light for a few snowy days and continuing but it's warmer. Some greens came in the house today for stir-fries

Steve