My arctic frost has been to 14 degrees totally unprotected. Almost total defoliation but so far no evidence of further damage.

Thanks, Ilya
I wouldn't pay that much for a mandarin tree, personally, but it's nice to know.... I have found out more about Artic Frost now and I'm not as excited about it. I'd rather have a premier variety of satsuma on a good known cold-hardy rootstock. I bought a Satsuma in a 3.5 gallon pot today for $29.98. Very nice tree with bloom buds swelling. But no indication of what the rootstock is! I have it from inside sources that it is on a citrange root, so that isn't too bad.
I have a Changsha seedling tree about 7 years old making fruit now. I like it pretty good, but want earlier-ripening fruit, in particular.
Thanks, again for your link.

Just picked up two Arctic Frost on sale today at the local garden center. I have two other satsumas in the ground that defoliated in the wicked cold we've had here. Hope they pull through, but if not, I'll graft Arctic Frost onto the surviving rootstock. The AF's appear to be rooted cuttings so it may be possible to get a couple more degrees of hardiness on FD rootstock.