May 1, 2020
I can provide an update now.
I left the tree right outside on my back patio over the winter, in a container, right next to an Ichang Lemon and Bloomsweet. For comparison, the Ichang Lemon and the Bloomsweet look great, nice healthy pretty green looking leaves that were kept throughout the winter, and have gradually continued to only green up a little bit more. (note to avoid any confusion: this is Ichang lemon, not Ichang papeda)
The "MIC" plant, however, does not look so good. The leaves are all very pale and white, and they will certainly drop. The stem of the plant is an unhealthy yellowish-green, unlike almost all my other hardy citrus varieties.
But I do see the beginnings of new growth buds coming out of the tips of the branches.
To be fair, I also have a small Valencia orange seedling that was left out there too, and it looks pretty similar, and looking very closely I can also spot the tiniest little starts of new buds on it. So these observations don't really prove this "MIC" is any better than a Valencia orange (which is not very hardy variety itself).
The one that I had previously planted in the ground was not able to survive the 2018-2019 winter, but that was a much colder winter than usual, with lots of snow which is unusual in this area. (Pacific Northwest, Olympia, WA, climate zone 8a)
Even though I did cover it with a paper grocery bag and 2 gallon bottles of warm water under there on the coldest night.
So this "MIC" hybrid, or at least whatever I was sent when I ordered 3 of them from the nursery, is not looking too promising.
And yes, it was specifically sold as hardy citrus, and obviously on rootstock, which I can only assume was poncirus or Flying Dragon.
(the nursery was far north of normal citrus territory, so certainly they would know all their customers would need hardy rootstock)
I guess with trials and experiments, we need to be able to deal with some disappointments.
This might come to your interest:
"It is well established that cold hardening occurs in citrus that
has been exposed to cool but not freezing conditions preceding
a freeze event (reviewed in Yelenosky, 1985)"
Well, that's very interesting, but I'm in the Pacific Northwest, and with the unique climate conditions here, the plants are definitely exposed to long periods of cold cool before it ever goes below freezing. Cold snaps are very rare also, because it typically takes a very long time into the year for temperatures to begin to consistently warm up. None of the hardy citrus has begun to bud out until just about now. Certainly temperatures throughout the winter and into early Spring remain below the temperatures needed for citrus to put on any growth.
This is reflected in the chill hour accumulation, we actually have 3400 chill hours (no that's not a misprint) due to temperatures remaining so constantly cool for so long.