For my spring fix I head to my green house. I have a wonderful hoop house covered with 2 layers of plastic. It is 48 feet long by 24 feet wide. There is a fan that keeps the layers inflated like a huge pillow. This forms an insulating layer of air. This is the first year we have tried to raise plants through the winter in the green house.
In September I planted edible podded peas. They grew quite well. The wooden post in the picture is 4 feet high.
For auxiliary heat we have used 4 space heaters. I have no idea if we wasted electric. The only night they did not keep the house above freezing was the two nights where the temps in our valley dipped to -5 degrees (it went to 22 inside the green house). During the day, if the sun is out, even if it is zero outside the green house will get to over 90 degrees. We need to check the house several times a day and provide ventilation. If it is cloudy it will still warm to at least 50 degrees when the out side temps are 15 degrees. Early in the morning we head to the green house to monitor the temps and turn off the heaters.
We found an inexpensive thermometer that registers the high and low temps in a 24 hour period.