So that little fellow made it without bring on a root stook. Go Keraji!
Yes, although it was covered, with a cut out clear plastic water bottle. Though it was a colder Winter than usual here and the covering was buried in snow. The top of the seedling almost completely got killed back, though one little leaf at the very bottom of the stem appeared to survive until April. And I do believe that leaf grew just a tiny little bit bigger. Unfortunatley due to an accident, the seedling got cut back down even lower towards the ground, so it lost that one tiny leaf that had survived through the winter. So what you are seeing now are little tiny leaves that have regrown since the start of July.
Another Keraji seedling that was somewhat bigger did not survive. It was also covered, but planted in a colder spot in the yard that did not get much winter sun (with the low angle of the sun in the winter making that spot more shady).
I know this may be a lot of detail, but all this specific detail is important to be able to infer things about exact level of cold hardiness.
The seedling that survived was maybe 5 inches tall, while the seedling that did not survive was maybe 6 or 7 inches tall.
The first seedling was killed back by the late February freeze to only 1 inch of live green stem, that was half brown on one side, but still had a tiny green leaf on the other side. Due to an accident, it then got cut down even lower, to maybe three-fourths of an inch.
So what this seems to show is that small Keraji seedlings, on their own roots, will probably not survive here very well, even when given some light cover. But it's probably just on the border of what they are able to survive.
I don't know if these experimental observations may be useful to someone else in another climate.
My limited experiments certainly seemed to suggest that Keraji has a little less cold hardiness than Yuzu.