This is my first year with an unheated greenhouse slightly larger than yours. I sowed it down a couple of months ago with clover and beds of grain (rye, barley, triticale) and legumes (vetch and Austrian peas) just to have some green in there this winter. All is doing well so far. The temperatures have dropped into the 20s inside a couple of times but always rise above freezing during the day (usually 10-20) above whatever the outdoor temps are when the sun is shining. I am not aware of anything that will germinate at those temps that I would like to plant now but I do hope to plant potatoes inside the greenhouse around the last of February and then some salad crops in either March or April. Good luck.

Are you guys planting in the ground inside the greenhouse or in containers? I just got my 10X12 greenhouse built and was thinking about what veggies to start.