This morning the temperature is about 2ºC below freezing — that's about +28ºF. This is the coldest morning we've had since January 7, and it's the first time since that date that we've been below freezing.
I went to check the greenhouse when I got up at 6 a.m. It was +3ºC in there. Not too bad, I think. The geraniums, jade plants, and other green things in there look okay at this point.
Even so, I set up an electric radiator in the doorway to provide the plants with a little more warmth. We've had this convection heater for a dozen years, but we've hardly ever needed to use it. I think I paid 15 euros for it way back when.
It's supposed to get colder and colder until at least the end of the week, so in addition to keeping the door between the (unheated) utility room open all the time, I'll turn the electric heater on low to make sure the plants don't freeze.