The Tropical Fruit Forum

Only problem is finding an pure ichang papeda to be the female parent...

There's a very big bush-tree in the Hoyt Arboretum in Portland, OR, right up against the side of the visitor center.
I can tell you it grows very easily from cuttings.

For those in SC, Woodlanders sometimes has some, although they're prohibited from selling to you if you're in GA.

Keraji seems pretty promising too. Maybe you could try using Keraji to pollinate a zygotic selection of poncirus hybrid and hope for the best.
Loch Laurel sells Keraji but they do not do mail order.

I'm in zone 8a in the US, at a similar latitude to you (well maybe just a little bit less far north than Mühlacker).
I have multiple varieties that have been in the ground for 3 years and none of them have fruited yet. Well, only two (the Sudachi and Keraji) of them have seemed to begin to form just the tiniest beginnings of little fruits, but they never ripened in time and eventually fell off.
Of course something hardier like citrange might behave a little different. My Dunstan citrumelo has a reached a fairly medium size and still no appearance of fruits. But grapefruits are known to take much longer until they begin producing fruit.

Due to your more continental location, the summers where you are do just get a little bit warmer than where I am. About only 2 degrees F (just a little bit more than 1 degree C) but that can make a difference. Maybe your plants put on more growth during the growing season.

See, I'm growing in the Pacific Northwest region, and while hardy citrus may easily be able to survive through the level of cold there, they just have trouble putting on much growth through the year, due to short duration of the summers and the cool temperatures throughout most of the year, it seems to me.

You can also wrap a mesh cage around the plant in a circle and fill it with dead dry leaves. That should help provide some insulation against the cold.
For example chicken wire.

The rough lemon I found had a very pleasant fragrant smell to it, like a sour orange, but had too much bitterness inside to eat.

These two trees are growing in someone's backyard in Federal Way, Washington, right next to Decatur High School. (Federal Way is just south of Seattle)
The owners are a Vietnamese couple.

One tree is grapefruit and the other tree is a lemon. They are both pretty big, about 6 feet high.

They said they grew both from seed. They are not on rootstock.

I asked them whether it was a Meyer lemon or a special lemon. They said no, it was just a regular lemon like what you buy in a supermarket, not special. Their language skills were not the best though, maybe they did not know.

They kept it inside the garage for 12 years during each winter before planting it outside. The woman said the trees have only gone through one winter outside so far. Both trees have a frame over them, which they cover during the winter. But they do not use any Christmas string lights.

They also have several small fig trees in their backyard.

The first picture is the grapefruit, the second one is the lemon.



pictures taken October 23, 2021

The location is not too far away from the water of the Puget Sound, and it's in a built-up suburban neighborhood, which probably helps keep the temperatures from dropping too low.

I didn't mean that Sudachi really tasted like lime. I meant it is a little lime-like in the same way that Yuzu is a little lime-like, and that combined with the sourness if it is picked green.
Maybe it's more accurate to say it can be used much the same way like lime. There is definitely at least a little hint of lime flavor in there though, but also in addition to that there is something green and unripe that tastes reminiscent of a lime type of flavor.
Of course the flavor overall is much more like a zesty fragrant sour orange.

Picture taken October 7, 2021


The crushed up leaves smell very pleasantly spicily fragrant, more mild and less harsh than the smell of normal citrus leaves.
I mean I could almost imagine the leaves being used as a perfume ingredient.

Here's the latest update
October 3, 2021



sorry for the low resolution images, was trying to fit 4 images into one picture to help reduce data space

A - tiny keraji seedling
B - Ichang papeda
C - Sudachi
D - ichangquat seedling (regular seedling)

The coloration on the tiny keraji seedling looks green and a very healthy color. However, this seedling just overall does not seem to be putting on any growth. It was the exact same size this time last year. The winters seem to set it back and then it recovers, but it does not seem to be able to grow to a size bigger than it was before. Those little leaves are all new. (There are five leaves, two of them very tiny)

Most of the leaves on the Ichang papeda are still very light in coloration, yellowish-green. I would say more yellow than green though they are still obviously alive. It seems they were never able to green up much since the winter. If you look carefully, there are a small number of newer smaller leaves that are a little bit more green in color but even those leaves do not look a healthy green. There are two of these Ichang papeda plants right next to each other and the leaf coloration on both looks exactly the same. Perhaps this variety begins to put out its new leaf flush too early in the year, when it is still too cold, and so the newer leaves do not develop the most healthy greenish color. When the very small new leaves initially start growing, they are a dark reddish color. I have never observed this growing them inside. It probably is a natural response to growing outside, either to the ultraviolet light of the sun or the cold.

The color of the leaves on the Sudachi look just okay. Not really the healthiest deepest shade of green, but okay, still definitely green and not yellowish. This little plant has not been able to put on much growth. It is a slow grower.

I may be mistaken about this but the Ichangquat seedling has not been able to grow any new leaves. All of those little leaves you see on the seedling are all old, from 3 years ago, the leaves that did not fall off (most of them did). But amazingly those leaves look like a healthy deep green color. It seems obvious those leaves have been able to recover. I think this seedling has almost not been able to put on any new branch growth. Yet the recovery of the leaves and the fact they have fully recovered their color since turning very yellowish during the winter is a good sign.

(This is the normal Ichangquat seedling, not the other one that seems to be hardier that I suspect is a hybrid)

I would say that all four of these are managing to survive, but almost not putting on much growth. Very slow growing. It seems they are marginal growing in this 8a Pacific Northwest climate. None of them were protected or covered this winter.

Bear in mind these are not big plants.
I took some measurements. The tiny keraji seedling is only 2 inches (5 cm), the Ichang papeda is 14 inches high (35-36 cm), the Sudachi is just a little over 16 inches (41 cm) high, and the ichangquat is 13 inches (33 cm) high but very narrow, with only 3 leaves.


The bigger keraji plant (not shown in the 4 images in this post) has one small yellow fruit on it, which seems not to have been able to ripen in time. It is less than an inch in diameter. (I mean it is completely yellow in color, not the slightest hint of orange-yellow)
It is still a small plant, so maybe the fruits will be able to ripen in future years. It is 17 inches (a little over 43 cm) high right now.

Here is a update picture of the Bloomsweet. It is growing and starting to reach some size and establish itself.




Here is the very tiny Keraji seedling that has survived in the ground for a few years without protection. It lost its leaves earlier in the year (perhaps due to slugs eating the leaves) but it has now regrown some new leaves. The leaves are small and not too big but look decently healthy. This thing is very small, about an inch, less than two inches high. I'm not sure if it will ever eventually be able to put in some size. It seems to suffer a setback after each winter, but then very late into the season, around late July, it starts to recover but then there is not much growing season time left in the year. It looks about the same now as it did the same time of year last year, and the year before that. But it is amazing such a tiny seedling is surviving and not declining.




Here is the bigger Keraji, more medium sized like something newly planted, that's grafted on rootstock.



It is doing well. It had tiny little fruit druplets begin to form but it looks like most of them dropped off.

pictures taken August 10, 2021

But, what would happen if I put FD on PT rootstock? Would the FD scion have a benching effect and die off or what?

The answer is probably a bit complicated, and a full answer would require a detailed explanation about how and why grafting results in what it does.

I very much doubt grafting FD on PT would result in any more of a dwarfing effect than trying to graft FD on FD.

It might be less heathy because regular PT is faster growing than FD. The rootstock might have some tendency to overgrow the scion, higher likelihood of longer-term incompatibility. But still not terrible since the two are still the same species and would be very compatible in other ways.

It might even grow faster, with regular PT for roots. I don't know. There could be two different competing factors here.

From talking with Nat Bradford, I know Taiwanica can easily survive the border of zone 8a/7b in the US South, and if it does suffer damage it will easily recover, but I'm not sure how it will do in the same zone classification further north in a cooler climate.
You should at least plant it in an optimal spot, not completely out in the open.

I have difficulty imagining it will like zone 7 Germany.
Could probably grow in zone 8a part of Germany, but not 7.

I doubt it's hardier than Yuzu, probably similar.

As for the Citradia, I'd imagine it would have no problem in 7b but not sure about 7a. Might suffer some damage most years but could then recover, due to its sour orange parentage which is pretty vigorous growing.

Disclaimer: I do not grow these two varieties, but have lots of experience growing many others, all different kinds, rare Japanese varieties and strange hybrids, so I think I do have some intuition on this.

Citrus does not need any sunlight to survive if the temperature is kept constantly below about 45 F.
Mature plants can survive through several months of dormancy like that.

Very small seedlings are different matter. I think it is unlikely they would survive.

But that depends very much on what your climate is and where you live.

Sun or shade might not make any difference if your small seedlings cannot survive the temperatures outside.

Your post and question is very confusing, for multiple reasons. Are you in the Southern hemisphere? What time of year are you talking about when you say "winter"? Telling where you are might help.

Sorry, but I'm not going to risk wasting effort to try answering your question without more detail, since the answer depends on several details.