what is the fine line?
Last winter here, it was 9-15 degrees at night for about 3 weeks, and not above freezing during the day for about a week of that. I'm really confused about why some plants can live in the ground here but not survive similar temps/conditions farther north? If a plant can handle 9 degrees here, why is that lethal elsewhere? It did snow once but melted the same day. Most winters here have no snow at all, so an insulating layer of snow is not a factor, and a lot of the plants had just a small bit of leaves as cover, some none at all besides their own dead leaves.
Gardenia, spider plant, purple heart (Tradescantia pallida, Amaryllis, elephant ears (Colocasia), cannas, Caladium, and so many others are fine this year after being in the ground last winter (and many other winters.) Why? Is it the length of exposure? Like if I walk outside for 2 minutes while it's 30 degrees outside, I won't freeze to death, but 2 hours and I would probably have serious frost bite and hypothermia. It seems like a solid week of subfreezing night and day *should* mean the difference between life and death for certain plants but yet they live. Isn't that sufficient for the top few inches of soil to freeze (especially up against a wall on the north side?) I just don't get it.