Yuzu

Bloomsweet

Dunstan Citrumelo

Keraji seedling

This very small seedling (barely more than inch high) is growing on its own roots, and went through the very cold last (2018-2019) Winter here. The seedling started off 4 inches tall, was covered with a clear plastic container, got buried under 14 inches of snow (very unusual to have that much snow here), and suffered severe die-back. But it did manage to recover and started growing by June of the following year. So it did prove such a small seedling was capable of surviving a very cold Winter here.

The following plants have not yet gone through a Winter outside here:

Sudachi

Ichang papeda (Citrus ichangensis)

Ichangquat (seedling from Ichang papeda x kumquat cross)

(All pictures taken today December 22)

For some additional context about how these different rare varieties are genetically / ancestrally related, you can see this thread:

origins of Asian hardy citrus types - diagrams

Additional past threads here:

I'm breeding new cold-hardy citrus varieties for zone 8

Some very cold hardy citrus hybrids

From the above reading, you have a challenge, I thought I have one. A greenhouse would be appropriate for the selection you grow. I hate to see them not prosper the way you want them to grow, than on the other hand you might know a answer. Wish you good luck and hope that members learn from you.

Cold hardy rootstock seams a popular topic now. My year around temps for citrus and tropicals never sees temps below 50.

Here's a little bit of research I was able to find about the origins of the obscure citrus species Ichang papeda:

" This species is cultivated in the vicinity of Ichang, and it bears a very large lemonlike fruit that is of sufficiently good quality to cause it to be shipped to markets several hundred miles distant.
In China this species occurs in an undoubted wild state in the hills of the Upper Yangtze Valley from Ichang west and southwest in Hupeh, Szechwan, and Kwichow, growing at altitudes of 1,500 to 6,000 feet. In Assam a closely related but slightly different form is found at an altitude of 5,000 to 6,000 feet in the Khasi Hills.
The species thus ranges over a region at least 1,500 miles long and some 500 miles wide.
This plant is reported in all parts of its range as growing in a truly wild state and is cultivated on a small scale around Ichang along the Yangtze River, where the fruit is called the "Ichang lemon" by foreigners.
The typical Citrus ichangensis as it occurs in southwestern China is a small tree or a large shrub, usually 5 to 15 feet high (1.5 to 5 meters), but sometimes reaching 20 feet. It also occurs wild in fruiting condition only 2 to 3 feet high on the cliffs of the Yangtze Gorges. "
<The article also makes mention to both a wild and cultivated form with slightly better fruit quality.>
" Mr. E. H. Wilson informs the writer that the form of this species cultivated in the Ichang region yields an excellent fruit known to foreign residents of the Yangtze Vallet as the "Ichang lemon." These fruits are shipped down the river to Hankow and west well into Szechwan, and are so much esteemed as to command good prices.
So far as is now known, Citrus ichangensis is native farther north than any other evergreen species of Citrus, only the deciduous Citrus trifoliata having a more northerly range. Besides having the northernmost range of any known evergreen species of Citrus it occurs at the highest altitudes reported for any wild species of the genus. In the Hsingshan District, in latitude 31° 10', Mr. Wilson collected this plant at an altitude of 4,200 feet, and Pére Cavalerie found it in central Kweichow at a height of 5,577 feet. "

excerpts take from: Journal of Agricultural Research, Department of Agriculture, Volume 1, Washington D.C., October 10, 1913. Citrus ichangensis, A promising, hardy, new species from Southwestern China and Assam, article by Walter T. Swingle

I'm looking at a map and the Chinese city of Yichang seems just a little further north of Changsha, about 320 km northwest.
That would lead me to believe that, while they may technically constitute separate species, the Changsha mandarin may just effectively be a natural evolutionary progression on the branch off between Ichang papeda and mandarins, which are native to the region a little bit further to the southeast.
Yuzu might possibly be on this continuum as well. Ancient Chinese texts refer to "oranges" (thought by modern scholars to be Yuzu) growing on the upper banks of the Yangtze river, and that area runs between the Yichang and Changsha area, much closer to Yichang than Changsha.

I think I'm just doing this to try to "push the boundaries" of what can grow here, since citrus is definitely not something one normally finds in this area. Citrus growers usually have to bring their plants inside over the Winter, or keep them in greenhouses.

I did visit a man in Vancouver, WA (right across the bridge from Portland, Oregon) who has a large Satsuma mandarin (Early St. Ann variety) tree that he covers with a frame, with string Christmas lights to help keep them from getting too cold in the Winter. He says the tree does produce fruits, and they get ripe enough for him to eat. I think where he is gets a very tiny bit colder than where I am.

I think I have a picture. This is Jim standing in front of his Yuzu tree in Vancouver, WA, somewhere around the middle of September. You can see quite a few green unripe fruits in the tree. The tree is a bit taller than him.

Though the fruits I saw on the Satsuma tree at the time looked very small green and unripe, so I was a bit skeptical about how much they would ripen. But to be fair, the previous Winter was a very cold one, so maybe the fruits began ripening later than normal this year, and trees in suboptimal conditions can be notorious for fruiting/ripening in alternate years.

(sorry, don't have a picture of the Satsuma tree)

Here is his Changsha mandarin tree, up against his home

Here's a close up of his citrumelo tree. He doesn't know what type of citrumelo it is, likely the less good tasting Swingle type.

You can see some pretty big but still unripe green fruits hanging in the branches.

I specifically asked him, he said he didn't use any protection for the Changsha and Citrumelo trees the Winter that year.

Interesting guy, maybe he shares a few pieces of sionwood for you to try. My winter lows could be anywhere between -15 to minus 6, so I have no choice as to grow them in my Greenroom with temps around 70. All winter long.

Following!

I did get a scion off his Changsha tree.

He grew five Changsha plants from seed, left the small seedlings outside one winter, only one of them survived. He later grafted that Changsha plant onto a rootstock (he can't remember which, probably either poncirus or citrange) and eventually planted it in the ground outside, up against his house. He covered the tree for the first two years, giving it a chance to grow without suffering too much cold damage. But I made sure to specifically ask and he told me he had not bothered to cover the tree the last time (it was not a mild winter that year). The tree you see in the picture is that tree.

He believes this seedling of Changsha that he selected might be slightly hardier than regular Changsha. But he is not really sure, and there's no real way to know at this point.

Just in case anyone was wondering, this is zone 8. I don't think any of these trees would make it in zone 7 this far so north, with the exception of course of Poncirus trifoliata, and possibly citrumelo in zone 7b. So if you live in a colder climate zone designation, this is likely not going to be possible for you.

Trying to grow these here in zone 8 in this cool climate region is already pushing things.

Update pictures taken February 26, 2020

Sudachi

Yuzu

Ichangquat

tiny Keraji seedling

Curious what became of the bloomsweet that you had in the first set of pictures? Was it sweet? I haven't seen that when I've visited Stan, but perhaps it's more a special order.

A boomsweet grapefruit on PT or FD should do well in zone 8a. Just be prepared to cover it when you get a 7A equivalent polar vortex.

Steve

you wanted to see the Bloomsweet?

here it is

March 1

It's probably the least hardy of my hardy citrus. Trying to grow this thing in zone 8a in the PNW is really pushing it, I think. wouldn't recommend this unless you're in zone 8b (if you're in a far northern latitude). I can just tell by the color hue of the leaves it's not as hardy as most of my others.

I'm just amazed it made it through the winter again. it wasn't protected this winter.

I seems that Spring has already started here, but it will be another two months until temperatures start remaining consistently warm enough for the citrus to start putting on growth.

I've seen some huge camellia bushes in bloom in the neighborhood, and the crocus bulbs flowered up about a week ago. The flowering cherry trees are budding out with green growth right now.

Your bloomsweet is probably grafted to C35. Grafted to ponciruswould give it an additional 5 F temperature drop.

C35

This is just my personal belief, but I believe compatibility level is very important. If your rootstock has a higher degree of compatibility, it will mean faster growth, better health. That's very important in this cool short season climate. C35 is obviously going to have a higher degree of compatibility than poncirus. I'm also experimenting with some own-root ones, to see how those fare.

I have this philosophy for all fruit trees, I don't like to use severely dwarfing rootstocks. The trees might get bigger, but they will also grow better, have better health, and likely live longer too.

For pomelos and grapefruits there's more specific reason they often prefer not to use plain poncirus rootstock.

Here's an update as of April 6, 2020

Sudachi

Ichang papeda, on its own roots

Both survived outside over the winter unprotected.

Sudachi is closely related to Yuzu, except the fruits are usually picked while still green.

"Bloomsweet grapefruit"

May 7, 2020

Look how much those old leaves have greened up since March.