last year I lost three 'sapphire skies' that I got from a local nursery due to the polar vortexes. they looked. I did not protect them. This year, I got a couple from "cactus king nursery online" -- straight species, and I protected them with an upside down pot. So far they are still green. Knock on wood, though, I have a Yucca treculeana that I protected in a similar fashion that's starting to get alarmingly squishy.