There are so many other climate effects on plant hardiness besides yearly minimums, that I've gotten to the point where I plant whatever strikes my fancy, and whatever lives, lives. Regardless of my "official" zone 7B, I have some zone 8 and 9 plants stubbornly refusing to die.

Mandarin oranges definitely are not supposed to grow here according to the "official zone", but oddly enough the two trees I have seem to be unaware of that "fact".

I also have a few other citrus types, palms, hibiscus, cannas, figs, etc.

Well, I think you're using the term "Mandarin orange" rather loosely (even though anything in Citrus reticulata could be legitimately commonly called a Mandarin orange).

'Satsuma' is a cultivar of Citrus reticulata that dependably fruits and survives/performs in zone 8b. However, 'Owari Satsuma' has even better cold hardiness, and 'Kimborough' is often cited as being even more cold hardy than 'Owari Satsuma'.

Perhaps you're lucky to be growing one of the latter two cultivars in your garden, Crispy_z7?

I have both Brown Select and Owari Satsumas and they have done good here without any protection. Even during a freak snow (we get one about every 20 or so years) and an ice storm we had last winter. My moro blood orange has done alright here too, it is blooming for the first time this year, I just hope this cold snap we are having now does not set it back, I covered it last night, I hope that was enough.

Gusolie:

Didn't see your reply till just now!

You are correct, I am growing Owari Satsuma mandarins.

And you are right on your other point- it does matter what type of mandarin. I have a few mandarin trees that I grew from seeds from a grocery store fruit, and these were killed almost to the ground in their first winter outside last year. This summer they have completely recovered, grew new branches and leaves.
These seed grown mandarins were basically for experimentation anyways. My hope is that they will grow as a low bush instead of a tree, as the freezing winds seem to be the biggest cause of damage.