It is 22 degrees outside right now at 8:45 a.m. There is nothing that grows in that temperature. I added a hotbox on top of my grow boxes. I planted Swiss Chard, Kale, and Lettuce back at the beginning of October. You can see they are barely coming up. I should have planted them earlier.
I also covered some plants I had already growing. This Swiss Chard is fine to add to soups or salads.
So, I still have them to enjoy.
My greenhouse is 55 degrees right now. 
I have also planted Tomatoes and Carrots in my Greenhouse in a pot back at the beginning of October as well. They are growing well. 
Chicago Hardy Figs growing in the Greenhouse. I pull the Figs and other plants outside in the Late Spring and pull them in again in the early Fall. See Bougainvillea below. 
You can also use a high tunnel with low tunnels 
right in the ground to grow cool season plants through the Winter. My Master Gardener friend Clarence did this years ago.
