The Tropical Fruit Forum

Possible hybrids would be interesting as a low-maintenance semi-edible ornamental that wouldn't have to be watered as often, for dryer climates.

According to some research that I looked into, the Australian desert lime probably has around the same cold hardiness as a Satsuma mandarin.

Where I am I'm not counting on ordinary citrus varieties. The Satsuma is inside a cold frame, which basically tells you I don't really regard it as a cold hardy variety (relatively speaking, compared to the others varieties I have). Well it is 47°N latitude so what would you expect?
Satsuma is a lot hardier than than other varieties but up here even it would be pretty "iffy", without protection.

Obviously the much cold hardier varieties are not good enough eating quality to have value for commercial production (compared to the type of varieties you find in supermarkets).

In this paper of DNA analysis the spelling is kabuchi ,not kubachi

My apologies, it is indeed spelled kabuchi.

In one DNA study I read, that kabuchi is kunenbo x citrus  yatsushiro in another kunenbo x something like citrus depressa.
Kabuchi is chance seedling from Okinawa.

That would be interesting, so it appears keraji is a triple backcross of kunenbo with some other original citrus. Probably some sour citrus I am guessing, maybe Yuzu.
(Edit: That original sour citrus appears to be Shikuwasa or a closely related hybrid of it, as per Hybrid Origins of Citrus Varieties Inferred from DNA Marker Analysis of Nuclear and Organelle Genomes, Shimizu T, Kitajima A.)

Kunenbo appears to be some sort of mandarin x tangelo hybrid, or something like it, analogous to the type of citrus known as a tangor (Temple orange and Page mandarin could also fall into this category). What I mean is that kunenbo probably has a buntan (pomelo) ancestor going back two or three generations. That would explain its fragrance. Whether it also may have some other cold hardy species in its ancestry (like Yuzu) I'm not sure. I will point out that it doesn't necessarily have to have been descended from a cold hardy species to develop a fairly high degree of cold tolerance over several generations. The central coastal region of Japan can get quite cold some Winters, every 25 years or so. That could have killed off the less hardy citrus. From there it would be natural selection as the citrus gradually started making its way up North, over successive generations. This would also leave me inclined to think that kunenbo is probably at least in substantial part zygotic, although I don't have any information on that.

Up in the Pacific Northwest it's been an unusually mild Winter this year. The forecast was that it would be particularly wet with lots of snow but it turned out to be unusually dry and unusually warm (relatively speaking). There was a light snow in early November, and later a fair amount of snow for just a stretch of four days in late February, but that was it. Not even any freezing temperatures the rest of the time in mid-Winter. One of my rose bushes had a few blooms on it on New Years Day, and there were also several camellia bushes with blooms on it. This definitely isn't typical. If every Winter was like this I'm sure you could grow a Satsuma outside, no problem.

Meanwhile I know you guys on the East coast were hammered by unusually freezing cold temperatures this year.

One practical effective way is to spray a dilute (1%) mixture of cedar, citronella, and clove oils, mixed with some red hot (capsicum) deer deterrent and possibly a little white pepper oil. Deer are strongly led by their olfactory sense, so certain types of smells will discourage their appetite and keep them away. The downside is the spray has to be reapplied every 10 days.

The temperature inside that little outdoor clear plastic enclosure I showed you earlier was 90 degrees F.
March 20, 3:40 in the afternoon, full sun, thermometer reading taken on the ground laying up against the small tree. The temperature right outside, in full sun, set on the ground, read 71 degrees. I was surprised it got that warm considering the weather service says the temperature is only supposed to be 53 degrees right now. Maybe it's because it's in a protected space, against a South-facing wall in full sun. And the dark colored soil also probably absorbs light more strongly than other surfaces, helping things remain warm.

A temperature differential of 21 degrees between the inside and the outside. Obviously in full sun the greenhouse effect is playing a very big role here.
Even for something that's basically as thin as vinyl shower curtain.

Just took a temperature reading in the night, 11:20 pm, inside the enclosure it's 51 degrees, that's about 3 degrees warmer than outside. (March 21)

Another temperature reading, today it's cloudy cold and drizzling rain. 50 degrees inside the enclosure, 47 degrees right outside. (in the middle of the day around noon, March 22)
It appears when it's grey and overcast the greenhouse effect and temperature differential is not as strong. The weather service says it's supposed to be 42 degrees right now.

so do you think my assuming that Yuzu/Pink Eureka Lemon might be a good rootstock would work?

I wouldn't necessarily make that jump. Lemons show different rootstock compatibility than mandarins and oranges.

Look, pretty much any citrus scion on any citrus rootstock will "work" but the compatibility will not be as good, and the scion may not be as vigorous, resilient, or productive.

I do recall reading that C. ichangensis seems to be closer genetically related to Citron than to other citrus. Genetically, Yuzu is about half C. ichangensis, while lemons are half descended from Citron. So on this basis one would think they might be compatible.

(quick note here, close genetic relation does not translate into similar cold hardiness here. C. ichangensis is one of the most cold tolerant citrus species there is, while Citron is more vulnerable to cold than common citrus varieties)

Flying Dragon helps force the scion into dormancy. I'm not sure this conveys advantage in zone 8b and higher (except perhaps in unusually cold winters).

Usually rootstocks are chosen for two primary reasons, that they are vigorous growing, and that they will have a dwarfing effect. The dwarfing effect induces trees to begin fruit production much earlier in their lives than they would otherwise. This isn't only true for citrus, it's true for all sorts of other fruit tree varieties as well.

Trifoliate or Troyer citrange are the most common standard rootstocks for mandarins.

just an update, it looks like keraji seeds are being sold on Amazon
https://www.amazon.com/Citrus-reticulata-KERAJI-MANDARIN-Hardy/dp/B01DA7A464

I just planted two of my keraji seedlings into the ground:



They grew from seed fast since they were under optimal growing conditions.

Check out this video: https://www.youtube.com/watch?v=2a9hpySojNM

This guy has Miyagawa Satsuma fruiting on Flying Dragon trifoliate rootstock in Virginia Beach, right on the edge of the water. He's got a bunch of other rare cold hardy varieties grafted into the tree as well, Thomasville citrangequat, Ventura lemandarin, Glen citrangedin, Ichang lemon, Dimicelli, Shikuwasa, etc.
He's had the tree for a few years.
Virginia Beach is in climate zone 8a.

The video was taken December 10 and the leaves were all green. By February the leaves all turned brown and shriveled up (as seen in another video). The East Coast got pummeled by a pretty freezing winter this year. The only scion that didn't lose its leaves was a Swingle citrumelo. The tree suffered a lot of damage but he says it looks like it will come back.

few quick notes:
Ventura lemandarin is believed to be a cross between taiwanica lemon x either Satsuma or keraji mandarin; Glen citrangedin is apparently a cross between Willits citrange x calamondin; Dimicelli is a cross between Clementine x either trifoliate or CiTemple edible citrange


I just checked the weather report and the temperatures in Virginia Beach this week are looking pretty similar to here (March 6-13). Well actually the average in Virginia Beach is a little warmer but the colder days are still the same.

We did end up getting freezing temperatures and some snow in the second half of February, but it only lasted a few days. Again, this Winter has been very unusual.

There was a genetic study in Japan that showed that Kishu was one of the parents of Satsuma. Kishu probably has less cold hardiness than Satsuma, however, since it was likely the other parent (kunenbo, also believed to be the parent of Keraji and Bloomsweet) that conferred cold hardiness. My guess is that the cold hardiness of Kishu isn't anything special compared to other mandarin varieties, but mandarins as a group do tend to be fairly cold hardy, certainly more so than oranges.