Here's a Yuzu I just planted
This Yuzu actually survived in a container, inside greenhouse when the roof completely collapsed in due to the weight of snow.
The greenhouse was still intact when the coldest temperature hit (12-14 °F), although the greenhouse had a lot of big cracks leaking in cold air. Just two or three days later there was even more snow and that's when the collapse happened, so there effectively was not a roof after that, it was open to the elements. This Yuzu (in the picture) lost all its leaves but later regrew them, being left in the container outside. Another Yuzu that was in there kept its leaves. (They are from different nurseries so might have to do with the rootstock)
I had to dig out the Satsuma that died, and planted this Yuzu in its place.
The Satsuma was covered throughout the Winter, up until early April. There were three gallon water containers in there, that never froze even during the coldest temperature drop in Winter. It was a colder Winter than usual, and with a deep blanket of snow, which is not usual here.
Here is a picture of the graft union on the Satsuma tree:
The Satsuma part is dead and brown, while the rootstock section right below the graft union is still a deep green. (June 9 )
It obviously was not a rootstock issue, the Satsuma scion simply was not able to survive the cold temperatures apparently.
This was up against a south-facing fence, in a warmer spot in the yard.
The Satsuma actually looked like it was likely going to survive, despite the leaves looking completely trashed, until the middle of April when the full damage started to become evident.
(The Satsuma was covered with a special clear vinyl plastic plant enclosure, it had a flimsy frame that quickly collapsed under the weight of snow)
So it looks like Satsuma (or at least a small Satsuma) cannot survive through the colder Winters here, even covered, with passive protection.
But Yuzu looks like it can survive, and even do very well with just the slightest bit of protection.
I actually went out there, just 3 or 4 hours before temperatures were expected to dip to their lowest point, and filled the three water containers with hot water and put them back under the covering. Apparently even that was not enough to save the Satsuma. This was late at night I went out there and there was no ice in the containers before I changed it out with hot water, which was surprisingly because there was already a foot of snow on the ground which had been there for a few days, and the days had remained cold.