This is the coldest morning of the winter so far here in the Saint-Aignan area. The temperature on our outdoor thermometer reads –3.5ºC. That's about +26ºF. Our outdoor thermometer is in a relatively protected spot on the north side of the house and reads a little high most mornings compared to reports we get on different weather sites on the Internet. I think this qualifies as a "hard freeze" — une forte gelée. Tomorrow the morning low temperature is supposed to be back above freezing, however.
One of the weather sites we consult lets people post the current conditions where they live. It's météociel.fr, and right now somebody in Blois, 25 miles north of Saint-Aignan, is reporting a temperature of –4ºC, and somebody over in Romorantin, 20 miles east of us, is reporting –9ºC (+16ºF). I don't know why it is often so much colder over in Romo, but it is. Other observers say it's –8ºC up in the Orleans area, 60 miles northwest of here.
The temperature in our recently built greenhouse is +3.3ºC (38ºF), with no extra heater on down there. The plants look fine. With the door between the greenhouse and the utility room open, the utility room is colder than it would be otherwise, but the greenhouse is warmer. It works for us. Outdoors, it's cold, but the Tuscan black "dinosaur" kale (above) doesn't seem to be much bothered by the freeze.