I left my yuzu seedling outside last year and it lost all it leaves but survived without any damage. I personally think that ichang padepa would be less cold tolerant than yuzu, and if this assumption is true, it surprises me.
I live in zone 8a.
Well, at least from what I've personally observed in the climate here, at least only going by how the leaves behave, it does seem like Ichang papeda is significantly less hardy than Yuzu.
This seems very surprising to me also.
I'm in zone 8a, but much farther north than you, in the Pacific Northwest (Olympia, WA), long period of cold and wet.
The leaves on the Ichang papeda all turn very pale and yellowish, with only the slightest hint of green. About half of the leaves fell off last year, and the other half eventually started slowly regaining a little bit of their color late into the year after temperatures had long since warmed up, but they never seemed to fully recover, and those leaves still looked yellowish and not the deepest shade of green, while the new leaves of that year looked better.
The Yuzu held onto all of its leaves last year, and they did seem to recover most of their color the next year. The year before that, during a very cold winter, the Yuzu may have lost about 30% of its leaves, but even then the other leaves that survived through winter later recovered.
I have not had the chance to observe bark damage on Ichang papeda yet to see if it is hardier than Yuzu in that way. Neither the Yuzu nor Ichang papeda suffered any bark damage or branch die-back this year, though the previous year the Yuzu did a little bit. (But the Ichang papeda was not in the ground yet that winter)
I have seen a big Ichang papeda tree 2 hours south of here in Portland, but it was right up against a visitor center building, and being near a big city might be preventing temperatures from going as low. And it was also planted in a spot well protected from wind. It's leaves probably looked similar to my Yuzu. But bigger trees often seem to display more cold hardiness, and it was a big tree.
The point is, I can't really say for sure that Yuzu is more cold tolerant than Ichang papeda.
I'm growing 4 Yuzu plants outside and 3 Ichang papeda, one in a container. So these are not just single plants I am talking about.
The Yuzu that were grown from seedlings growing on their own roots still appear to be doing better than my Ichang papeda.
Sorry to make this so complicated, but I am trying to give all the relevant details in case anyone wanted them.
I am thinking it might still be possible than Ichang papeda could be able to survive more absolute low temperatures, but maybe just does not do as well in cold overall.
Another possible contributing factor might be that Ichang papeda's roots might not be as tolerant to high levels of moisture during the winter, which might be making its leaves look more yellow than the temperatures alone would cause it to look. The climate here does have wet winters, whereas its native climate in China has drier winters.