Ooooh that is cold trail
I had to go work that out in Centigrade and it comes to -23.
If you spit does it freeze before it hits the ground or does it need to be colder for that to happen?
Come on Sola Trail need his greenhouse up and running again.
BTW Trail would black plastic sheeting on the walls and floor help heat up the green house and maybe get you a week or two of an earlier start?
All that black would surly heat it up a bit but I gues you'd lose that heat at night.
Having said that I have a paraffin greenhouse heater to keep the night time chills from cooling down early season seedling etc.