Jade Plant Cold Hardiness

[Subrosa]

While trimming a small shrub I came upon a pair of pots that I had forgotten about since last year. Not a question that they both have been outside since the end of last summer. Both were severely overgrown with weeds, and when I cleared them out I found one contains a specimen of native Prickly Pear, Opuntia humifusa. No big deal, they're extremely hardy. However in the pot along with the Opuntia, and in the other as well are small but healthy Jade Plants, Crassula sp. Now understand that I live in zone 6B, and we just went through The Winter From Hell. The pots were somewhat protected being under an evergreen shrub at the base of a south facing brick wall, but even that trick is only good for a zone or so increase. I was under the impression that Jades aren't remotely cold hardy, and that a freeze would end them. I GUARANTEE that those pots were frozen solid 24/7 for a week at a time at least twice last winter, and saw temps in the low single digits. Anyone else have a similar experience?