Frosthardiness experience with citrusvarieties in zone 7, down to 3,2 F

[tedburn]

Christmas greetings with the final picture of my
first fruiting inground Keraji.
The fruits are now nice yellow and good balanced sweet /sour.
More unripe there is for my opinion a slight skunky taste in the rind,
not in the fruit. More and more ripe also the skunky taste in the rind gets
lost. Last only a bit bothering are the amount of seeds , 1-3 per fruit segment.
So final conclusion, Keraji is one of the best citrus for
colder climates in ground.

[BorisR]

Interestingly, last year I had only 10 seeds in 20 fruits. Keraji is self-incompatible and form nucellar seeds in the presence of foreign pollen. Have you had any pollinators nearby?

[tedburn]

Yes, for some time I had clementines nearby.
Didn' t know, that keraji is with much seed if crosspollinated.
So perhaps try to keep it a bit separated next summer 😉.

[tedburn]

Nice surprise,
among my Flying dragon seedlings from fruits of a citrus friend
seems at least one hybrid, due to very different leave shape.

[usirius]

good to hear that fruits can endure -2/-4 without damage  do you have fruits of other varieties which got the same temp.?
do your plants get wind or are they in a greenhouse?

last year I got an overwinteres meyer lemon which got about -3, the fruit was fine.

There is a Yuzu from a selection by a plant lover from various fruits selected and brought from markets in Korea and in the hinterland. It is planted in Germany near Cologne, completely without protection. According to previous experience, the fruits could withstand -11°C. Just one degree colder would destroy them, and they turned to mush after thawing. I assume that the sugar content and other ingredients bring the freezing point well below 0°C, which could explain why the fruits can withstand greater cold without damage.

[tedburn]

Just a short update to the German winter 2024/2025.
Up to now it was relative mild with some freeze days with
deepest temps down to - 10 ° C. No problem even to my
unprotected citrus. Two of the unprotected see pictures below.
Now only hoping that February brings no negative surprise anymore.
 
3 year old seedling, Ichangensis SRA 241


Morton Citrange/ Fa5 since 2020 in ground, slow growing

[tedburn]

Tonight last day of February freeze.
So winter 24/25 seems over with cruel temperatures.
Still some freeze days and night temperatures down to -8 °C didn' t
hurt anymore. So this winter no damage at all at my citrus
in ground, very happy  .

Ichangquat 245, autumn flowers not frozen


Multigraft on flying dragon


Not protected grafts of IPPTS (Ichang Papeda x Poncirus x Satsuma) left, only litle bit chlorotic and citrumelo Trifolis right side

[tedburn]

After still a few days with night freezes to -6° C,
now the forecast for the following weeks
is spring, without night freezes and daytime temps
> 15° C.
So time to free the citrus (from winter fleece),
and as posted before  no damage for the inground
Citrus. Seems good start in the Citrus season.

Left multigraft on Flying dragon, in the middle Ichangquat 245 and Ichangstar right



From left to right - Keraji, Nippon Orangequat, Thomasville (left of fig trunk), Bigraft Bloomsweet/Staraji55
and Orange Slava Micurina

[bussone]

Looks like my Morton didn't make it, but I'm not sure the cold was what did it. It wasn't all that happy in late fall when it went under the nets, either.

The Prague and the Thomasville look okay, although the Thomasville lost a bunch of leaves at the bottom, away from the heat lamp. The unlabeled citremon did surprisingly well, but we'll see what spring brings.

[tedburn]

Sorry to hear that of your Morton.
I made the experience that rootstock Flying dragon and very late morning sun
in winter and spring is a good thing and helps the plants a lot.
How cold did you get ? 

[bussone]

Sorry to hear that of your Morton.
I made the experience that rootstock Flying dragon and very late morning sun
in winter and spring is a good thing and helps the plants a lot.
How cold did you get ?

7F or so. The Morton was unheated (too far from the house).

The poncirus was totally unprotected, in the front yard. It still has a couple of leaves on it and looks perfectly fine. (It didn't leaf-drop at all last winter)

None have started putting out shoots or buds, although it looks like the citremon is ready to do so. The Prague looks scrubby, but it always does.

[tedburn]

I' m a little bit astonished th ;)at your morton died with 7°F.
In my climate it withstood 3° F with fleece protection in
2020/2021 but as smaller new planted plant with damages on
rootstock FA5.
But in every case there are differences in every plant, rootstock or scion and in
Plant fitness before freeze, and other parameters...
But final Morton is very freeze tolerant and perhaps you could
give a second try 

[bussone]

I' m a little bit astonished th ;)at your morton died with 7°F.
In my climate it withstood 3° F with fleece protection in
2020/2021 but as smaller new planted plant with damages on
rootstock FA5.
But in every case there are differences in every plant, rootstock or scion and in
Plant fitness before freeze, and other parameters...
But final Morton is very freeze tolerant and perhaps you could
give a second try 

Like I said, I don't think it was the cold that killed the Morton, really. I think it was dying towards the end of fall. It hadn't been happy for much of the summer. I'll try again with another, I think.

[a_Vivaldi]

Like I said, I don't think it was the cold that killed the Morton, really. I think it was dying towards the end of fall. It hadn't been happy for much of the summer. I'll try again with another, I think.

Yes, unfortunately sometimes a tree will fail to thrive for some unclear reason. I had a Changsha that was in poor health no matter what I did to it, always yellow and almost never growing. It died the first winter it was outside, even though our low that year I think was 16 F which Changsha should survive normally.

[tedburn]

Yes I also had some inground citrus which died after winter ,
where I think due to problematic rootstock - one poncirus rootstock
with grafted HRS899a died in first winter around graft unit.
Other Poncirus with Keraji on it got phytophora, had to cure and
cut half of the plant and now 3 years later wonderfull plant with
lots of fruits and looks pretty and healthy.
So I agree, that lots of (winter) dying plants are often not due
to cold hardiness but problems before, combined with winter stress.
Good luck and lets keep on trying and fighting for our inground citrus in
the hardier zones  .

[tedburn]

Today graftet my first own crosses Chandler x Bloomsweet wich took -8 °C as 1 year old seedlings.
But the 3 survivors needed 2024 to recover and now seem to be again in
pretty good shape and thrive.
Two of the 3 seedlings had more twigs, so
it was possible to take a smal scion of them
for grafting.
Now looking forward for further good and faster
groth on Poncirus and Citrumelo 5* rootstocks.

Before grafting


After grafting and added variety badge

[bussone]

Looks like my Morton didn't make it, but I'm not sure the cold was what did it. It wasn't all that happy in late fall when it went under the nets, either.

The Prague and the Thomasville look okay, although the Thomasville lost a bunch of leaves at the bottom, away from the heat lamp. The unlabeled citremon did surprisingly well, but we'll see what spring brings.

I may have spoken too soon above about the Thomasville.

The Prague and the unlabeled citremon are doing fine. The Thomasville looks unhappy -- the rootstock is fine; it has sent up a small shoot that I've left alone for the time being. The Thomasville graft looks to have a bark split low on the main stem, and its looking like its going to drop most of its leaves. I'm thinking it may not make it.

It's funny. I expected the Morton and the Thomasville to do fine and assumed the citremon would just die, with the Prague struggling.

Totally the opposite. Morton died; Thomasville is doing poorly. The Citremon tanked it like a champ, and the Prague looks better than it did last summer. I just have zero idea...

[tedburn]

Sometimes its strange how some cultivars make it and others don't.
I planted seven  2,5 yr old seedlings Citrumelo N82 last early summer at the same place
within a m2 in ground and left them unprotected this winter, all
about the same size.
3 showed nearly no damage, 3 looks a bit stressed and one
 died with bark crack.
So I think a selection with citrus cultivars make sense and I assume
same cultivars sold in different locations may show different
Cold hardiness or fruit taste due to zygosity.
Picture with the 6 survivors, died one already removed.

[tedburn]

Help needed  ,
Below are my citrus with flowers and I would
ask you what would be your suggestions
for crossing, with the goal of good tasting
and as much as possible frosthardy under
respect of zygosity. Chandler x Bloomsweet
and Yuzmelo x Bloomsweet I made
already the last years.
I'm curious to your suggestions 

Flowers 2025
Clemyuz 22
Trifeola - Pollen (small plant)
5* Citrumelo
Bloomsweet
Oroblanco Grapefruit
Rio red Grapefruit
Sanford Curafora
Yuzu
Keraji
Newhall Orange 
Satsuma sotchi
Yuzu N30 - Pollen
Slava micurina orange
Dimicelli ?
YuzuxCitrumelo ?

[Rei]

I'd personnally try to cross Oroblanco with 5Star or Yuzumelo, as it could have a grapefruit-like fruit, and inherit the low acid levels of Oroblanco.

I think Clemyuz x Bloomsweet sounds interesting too. It would likely lead to something hardier than Bloomsweet, with some of the aromatic notes of yuzu.

[Florian]

I think Yuzu x Keraji or viceversa could be interesting too.

[tedburn]

Thanks Rei, Florian and Skandiberg for your suggestions,
I added them on my list  .
Very challenging due to a lot of opportunities,
but also very happy to have these opportunities.

[Mulberry0126]

I think Yuzu x Keraji or viceversa could be interesting too.

I second this, I am interested in such a cross. It would be like re-creating the circumstances for Clem-yuz 2-2 but with another, hardier mandarin. The result would probably be very good.

[a_Vivaldi]

I think Yuzu x Keraji or viceversa could be interesting too.

I second this, I am interested in such a cross. It would be like re-creating the circumstances for Clem-yuz 2-2 but with another, hardier mandarin. The result would probably be very good.

I've not tasted Keraji, is it as sweet and juicy as a clementine? I think that's a big part of why Clem-yuz 2-2 works, the clementine fruit quality really comes through. Then again, Yuzu is aromatic enough that maybe a Kerjzu or Yuzjrui or whatever Yuzu x Keraji should be called (Kyerziju is my preference haha) would stand on its own as a culinary fruit.

[Mulberry0126]

I think Yuzu x Keraji or viceversa could be interesting too.

I second this, I am interested in such a cross. It would be like re-creating the circumstances for Clem-yuz 2-2 but with another, hardier mandarin. The result would probably be very good.

I've not tasted Keraji, is it as sweet and juicy as a clementine? I think that's a big part of why Clem-yuz 2-2 works, the clementine fruit quality really comes through. Then again, Yuzu is aromatic enough that maybe a Kerjzu or Yuzjrui or whatever Yuzu x Keraji should be called (Kyerziju is my preference haha) would stand on its own as a culinary fruit.

The fruit I tried was from a young tree, so I have yet to taste it at its best, but the fruit I had was mildly sweet and juicy with a taste reminiscent of a pomelo actually. I think that the flavors would be very complimentary, and Keraji did have a strong mandarin scent to it as well.