F2 citrange winter hardiness trial

[kumin]

This week's outdoor photos showing responses to cold weather to this point Jan 06, 2022


Citrange 001: One of the hardiest trees, initially evergreen, becomes deciduous with age.


Another Citrange 001


Citrange 006 Deciduous and quite hardy.


Another 006


Another 006


Additional 006


010 Among the hardiest


011 tetraploid and very hardy


Another 011


024 Evergreen when young.


Another 024


Additional 024


028: Failure: all the 028 plants are in poor condition

Another 028: failure


054 Rather good condition. Some bark splitting.


067: most Citrus-like in this test, high grafted on Poncirus, showing a bit of stress. Second year graft.


5* Citrumelo: looking okay at this point. High grafted on Poncirus. Second year graft.


A-026 acceptable hardiness, this selection is the first of the Citranges to flower and fruit.


D Citrange: hardiness is variable, late growth is cold sensitive, mature growth is quite hardy.


2 Survivors in the original test plot. Unnamed at present, one is fully deciduous, one is evergreen.


Outdoor TaiTri high grafted on Poncirus. Second year graft.

[hardyvermont]

This is fascinating, how cold has it gotten so far?  Looking forward to seeing how well they make it though the rest of the winter. 

[kumin]

The lowest temperature to date was 9°F (-12.7°C) this morning. Snow cover often leads to lower temperatures, as we got our first snow yesterday. The previous lows were 17°F (-8.3°C). Being located in a semi rural area, official low temperature forecasts are unreliable on calm, windfree mornings.
We will be entering the time of year that's most challenging to overwintering plants. Frozen soil, increasing windiness, as well as increased sunshine will cause more damage than the weather has done up to this point.

[kumin]

A-026 seedlings starting to emerge. Uncertain what percentage are nucellar.


Small germination box with thermostat probe in one of the pots to prevent overheating. There's a heating mat on the bottom with heavy aluminum baking trays on top of the mats to keep the heat distribution uniform. Thermostat setpoint is 86°F. (30°C).

[Walt]

Sounds like a good set up.  This year I've just put seeds in 72 cell trays and put them on top of the refridgerater.  It has worked ok. but there is only room for 4 trays at a time.  Nrxt year will be better.

[kumin]

Recent photo of #002 segentrange showing minimal thorniness. There are a few short thorns present on some branches. This seedling has good hardiness. It is more difficult to get good "takes" when grafting this selection. The tips of the leaflets have a notched indentation.


#128 a deciduous outdoor survivor showing no damage after repeated lows of 5°F (-15°C). Although trifoliate, it has uniquely shiny leaves during summer.



Glossy leaves on #128 segentrange.



A Meyer lemon seedling showing the effects of repeated low temperatures in the cold frame.
The trifoliate leafed tree in the upper left corner is a 5*Citrumelo.

[tedburn]

very interesting your different crossing varieties, which shows a really good success for frost hardiness and perhaps more interesting fruits than poncirus. Also very interesting your Meyer seedlings, which lows did they take in the last winters ?  Because I also have one year old Meyer seedlings and thought about planting them testwise in open ground in zone 7 not sure if they will survife  a middle winter ? But waiting 10 years for fruit or rootstock are no good alternatives  .

[kumin]

Tedburn, the previous Winters may have had temperatures at -10°C in the cold frame for a short duration. This Winter has been both colder and the cold period has been of longer duration. I used frost cloth for protection until this year. The trees are much too tall to cover at present, unless it were installed at roof height. The Meyer was included simply for comparing the F2 selections to standard Citrus. It's serving it's purpose.
You bring up a good point in looking at optimistic outcomes vs realistic outcomes. For me it boils down to a goal of Citrus fruits on Poncirus trees. The question is how soon and how close that rather lofty goal might be achieved.

[tedburn]

Kumin, thanks for your reply, and I fully understand and support your goal for citrusfruit on poncirustree.
But for me it still would be interesting to which low temperature your meyer seedlings could withstand without getting died by freeze, only as orientation, because as far as I know meyers should die by freeze below - 6° C as different sources mention, I didn' t freeze tested them.

[kumin]

Past years aren't a good reference, as I used 4 layers of frost cloth. That should have trapped warmth underneath. So based on this Winter, my recollection is that the first sign of leaf damage was around -5°C. Subsequent cold nights added to the damage, even at similar temperatures. I didn't pay a great deal of attention to it as Meyer lemon is peripheral to my interests. If I had to give a response, I would suggest that the severe damage coincided with the surface of the soil freezing.

[tedburn]

Thanks Kimun, so this confirms that meyer is concerning freezes very limited.

[kumin]

At least 2 of my 5 Poncirus+ 3 year old seedlings will be flowering this year. Hopefully, there'll be some fruit setting. There will be quite a few A-026 flowers on a 4 year old seedling.

[mikkel]

This is impressive!

[tedburn]

very nice such early flowering 👍. What are the secrets if this early flowering ? I assume all your plants are in open ground ?  So what are the other parameters for early flowering of seedlings ? Regards Frank

[kumin]

The plants are in an unheated cold frame. The plastic film at the ends of the structure is removed during the Summer. Nevertheless, the inside temperatures are higher than the outside temperatures. Additionally, I feed with foliar fertilizer during the Spring and Summer, but not Autumn, as late growth is susceptible to Winter freeze damage.

[kumin]

I assume all your plants are in open ground ? Frank

The large plants are in open ground. Last Summer's grafts are in pots. Only the trees planted in the soil are flowering, and only a few of them are flowering this Spring. The trees in the cold frame are 2-3 times as tall as the outdoor plants, but less stocky, the increased node counts likely contribute to the precocity.
My guess is that a number of additional plants will transition to mature phase this Summer.
The next several nights are forecast to have near record low temperatures, some as low as -6,6C (20F). This might be challenging, as there's some early bud-break.

[tedburn]

Thanks Kumin for the explanation  , we also had now more than 2 weeks of challenging weather, days with 15 ° C and more and nights or mornings down to -5 ° C, so I akso had to cover the plants in pots already on terrace with flees to protect the already growing buds. But now freeze us finished for the next days.

[kumin]

A-026 segentrange twigs full of flower buds. This tree is 4 years old this month. The seeds are nucellar, but the pollen should be fertile. This tree flowered last summer and is the first to fruit.


Flower buds on the 3 year old Poncirus+ seedlings, 3 out of 5 seedlings are ready to flower, but may not all have pistils in the flowers.


Nucellar A-026 seedlings from last summer's fruit.

[kumin]

2 additional trees from the outdoor trial in 2018/2019 have produced flowers:


Conestoga 010 with flower buds, not certain if these will have pistils and ovaries or only anthers. This selection is among the very hardiest.


Conestoga A-026 is blooming prolifically. This tree produces seeded fruit, but all seeds appear to be nucellar. Pollen is fertile, however.


Conestoga 006 first flower, unfortunately there's no pistil in the flower. Not unusual for first flowers. This selection is very slightly less hardy than Conestoga 010 and 011.


Poncirus+ flowers, being the first flower, about 80% are missing the pistils.

An observation regarding Conestoga 001 and 058: these 2 selections don't have the Winter bud scales present on Poncirus. Conestoga 001 is very hardy and reluctantly deciduous as the trees grow larger. Conestoga 058 is the most Citrus like. evergreen and the least hardy, but quite vigorous. Since these 2 selections lack scaly Winter buds, I expect them to flower during the initial Spring flush as conventional Citrus does.

[tedburn]

congratulation to your breeding success and the early flowering plants and thank you for your very interesting reports 👍

[mikkel]

You really seem to have the right conditions for Poncirushybrids. Congratulations! I'm very excited to see how it goes.

[kumin]

Mikkel, with the limited amount of flowering options at present, I'm using Poncirus+ as a seed parent and Conestoga 006 and A-026 as pollen parents in crosses at the present time.. Conestoga 010 should be flowering within about a week and could potentially be another parent. I also have thousands of regular Poncirus buds within a week of blooming, but might not use, except potentially as seed parents.
Differentiating between 100 % Poncirus and 75-80% Poncirus might be quite a challenge!

[Walt]

The grafts your F2 citranges you sent last summer are showing new growth today.  They n were not exposed to a trae Kansas winter.  They were protected from the worst.  But they went dprmant,
Too soon to know if they will bllom.
I'm wanting to graft each to my  8 year old Korean Pt.  While Pennsylvania and Kansas are both zone 6, there are differences in daily temperature fluctuations etc,

[kumin]

Hopefully, we're getting close to our last freezing weather. There is no apparent recent cold damage at this point.
This morning's low temperature was 26°F, I started the sprinkler system at 1:00 AM during the night. There was a heavy accumulation of ice, but everything looks fine.

[kumin]

You really seem to have the right conditions for Poncirushybrids. Congratulations! I'm very excited to see how it goes.

Mikkel, I would attribute the adaptation of these hybrids to the severe selection pressure presented by the survival of several dozen individual trees out of 20 000 original seedlings.
In a sense, it's an accelerated form of the natural selection process. In nature these processes are constantly driven by disease and other environmental factors. In this case the predominant factor is cold temperatures.