Growing rare cold-hardy hybrid

[SoCal2warm]

I'd like to post a quick picture of 3 of a very rare variety of cold-hardy citrus I have. It's a CiTemple 'edible' cross with Ichang papeda, that was then crossed with Minneola tangelo. (Well actually, to be more exact, it's a seedling grown from one of the fruits)



So far the 3 plants haven't fruited yet, and I still reserve a little bit of skepticism that the plants are as claimed, just because the existence of this sort of hybrid is incredibly unusual. I'll fruit them out and report on the fruit quality and cold-hardiness later. There's potential here that this could be the "holy grail" of cold-hardy citrus.

I have two inside a grow tent (to make sure they put on growth over the Winter) and one outside in the greenhouse. So far this cold-hardy hybrid doesn't really have an official name.

(CiTemple is a specific cultivar of citrange, in case anyone reading here was not aware)

[Sylvain]

>  So far this cold-hardy hybrid doesn't really have an official name.
It is MIC. Not so rare... 

[SoCal2warm]

planted one in the ground:

[SoCal2warm]

here's the other one growing inside



it seems to have a fairly vigorous growth rate

[lebmung]

I think a seedling should be exposed to cold early to adapt.
The foliage seems to be light  green, is this a trait or deficiency?

[SoCal2warm]

I think a seedling should be exposed to cold early to adapt.

That definitely seems to be true. Leaves and stems that have grown under warm (and humid) conditions inside do not seem to be to tolerate being outside.
I speculate that the plant tissue somehow becomes permanently adapted to the conditions it grew under.
Bringing it inside under optimal conditions is a great way to accelerate growth, but then all this new growth on the plant does not seem to be able to survive well outside, so there's a big setback when it is finally moved outside. In the Summer here, the outside air is much drier, while much of the rest of the year experiences cold/cooler temperatures especially at night.

The foliage seems to be light  green, is this a trait or deficiency?

The tree was left outside and the leaves had begun turning yellow due to cooling night temperatures, so it was finally brought in.

[lebmung]

The tree was left outside and the leaves had begun turning yellow due to cooling night temperatures, so it was finally brought in.
[/quote]

Check the root system fot hte one outside. The one inside I think it has N deficiency coupled with poor light conditions. I have kaffir lime who stay outside at 5C and they don't turn pale or yellow. Of course these are from seed acclimatized over 4 years. The ones grafted with scion from Thailand, don't stand a chance outside.
To make a plant hardier, I believe one must stress it. Cold, dry, little light then recover with warm, moist soil then again stress it. The plant will learn to adapt to survive. Plants don't run like animals, they don't hide, they adapt. Growth retardants are also good.

[SoCal2warm]

I have kaffir lime who stay outside at 5C and they don't turn pale or yellow.

I believe these are on FD trifoliate rootstock, so that may have something to do with it. The rootstock may be forcing the plant into dormancy.

Although the leaves on my citrumelo have not turned yellow yet. (it's also on rootstock, do not know which type)

[Citradia]

The leaves on my trifoliata trees don’t turn yellow nor do my citrumelo or citrange trees. They stay green mostly until they succumb to severe cold, low teens or single digits. Some leaves on trifoliata turn red and yellow/ orange eventually in winter with some still green at top of tree over winter. Citrange leaves freeze and wilt while green and fall off. Similar to peach and apricot, leaves drop green. My meiwa and satsumas on dragon stay green all winter although protected while they stop growing due to dormancy. My flying dragons don’t turn fall colors either unfortunately, leaves just drop green. 39 degrees here this morning, been in 40s all week, and my trifoliata and dragons are green as grass while sugar maple is colored up.

[Florian]

I have had poncirus that turn yellow and others that don't but I never gave it much thought.. My largest FD does show beautiful autmn colours.

[SoCal2warm]

The leaves on my trifoliata trees don’t turn yellow nor do my citrumelo or citrange trees. They stay green mostly until they succumb to severe cold, low teens or single digits.

Most of my trees do turn yellow. Then again, most of them are not citrumelo or citrange or anything else that has trifoliate in their ancestry.
(I've kind of been focusing on unusual cold hardy citrus that do not have trifoliate in their ancestry, but that might also mean the leaves are not as adapted to staying green in cool temperatures)

[hardyvermont]

Poncirus in New England tended to stay green, some all winter.  These were smaller plants, and trees also seem to become more deciduous as they get older.  In the south, some are turning color now, and more will color up later.  I have speculated that the rapid onset of cold in the north keeps them from forming an abscission layer.  At the Arnold Arboretum there are two Poncirus growing next to each other, and as shown in a photograph in the old forum, one tree kept its leaves in the winter, the other did not. 

[lebmung]

This might come to your interest:
"It is well established that cold hardening occurs in citrus that
has been exposed to cool but not freezing conditions preceding
a freeze event (reviewed in Yelenosky, 1985)"

[SoCal2warm]

May 1, 2020

I can provide an update now.

I left the tree right outside on my back patio over the winter, in a container, right next to an Ichang Lemon and Bloomsweet. For comparison, the Ichang Lemon and the Bloomsweet look great, nice healthy pretty green looking leaves that were kept throughout the winter, and have gradually continued to only green up a little bit more. (note to avoid any confusion: this is Ichang lemon, not Ichang papeda)

The "MIC" plant, however, does not look so good. The leaves are all very pale and white, and they will certainly drop. The stem of the plant is an unhealthy yellowish-green, unlike almost all my other hardy citrus varieties.

But I do see the beginnings of new growth buds coming out of the tips of the branches.

To be fair, I also have a small Valencia orange seedling that was left out there too, and it looks pretty similar, and looking very closely I can also spot the tiniest little starts of new buds on it. So these observations don't really prove this "MIC" is any better than a Valencia orange (which is not very hardy variety itself).


The one that I had previously planted in the ground was not able to survive the 2018-2019 winter, but that was a much colder winter than usual, with lots of snow which is unusual in this area. (Pacific Northwest, Olympia, WA, climate zone 8a)
Even though I did cover it with a paper grocery bag and 2 gallon bottles of warm water under there on the coldest night.


So this "MIC" hybrid, or at least whatever I was sent when I ordered 3 of them from the nursery, is not looking too promising.

And yes, it was specifically sold as hardy citrus, and obviously on rootstock, which I can only assume was poncirus or Flying Dragon.
(the nursery was far north of normal citrus territory, so certainly they would know all their customers would need hardy rootstock)

I guess with trials and experiments, we need to be able to deal with some disappointments.

This might come to your interest:
"It is well established that cold hardening occurs in citrus that
has been exposed to cool but not freezing conditions preceding
a freeze event (reviewed in Yelenosky, 1985)"

Well, that's very interesting, but I'm in the Pacific Northwest, and with the unique climate conditions here, the plants are definitely exposed to long periods of cold cool before it ever goes below freezing. Cold snaps are very rare also, because it typically takes a very long time into the year for temperatures to begin to consistently warm up. None of the hardy citrus has begun to bud out until just about now. Certainly temperatures throughout the winter and into early Spring remain below the temperatures needed for citrus to put on any growth.
This is reflected in the chill hour accumulation, we actually have 3400 chill hours (no that's not a misprint) due to temperatures remaining so constantly cool for so long.

[SoCal2warm]

Whatever it is, it's recovering and beginning to put out new leaves.


To the right in the picture, off to the side, you can see an Ichang Lemon for comparison.
Whatever this thing is, it definitely appears not to be as hardy as Yuzu, and less hardy than Ichang Lemon. But it does appear to have survived.

From the intermediate level of hardiness this demonstrated, I feel fairly confident the nursery did not simply make a mix up with some other common citrus variety, or another common hardy citrus variety.

I'm thinking this could have promise if it was crossed again with some other hardy variety.


Edit: On second thought, I'm not so sure. Even my Valencia Orange and Reinking pomelo seedlings, that were left out on the patio over the winter, are beginning to put out some new leaf growth.

[SoCal2warm]

Poncirus in New England tended to stay green, some all winter.  These were smaller plants, and trees also seem to become more deciduous as they get older.  In the south, some are turning color now, and more will color up later.  I have speculated that the rapid onset of cold in the north keeps them from forming an abscission layer. 

Rather I would speculate that it may be just the opposite. In the North, temperatures begin consistently going down long before the first frost. Whereas in the South, the temperatures can fluctuate more between warm and very cold days. It is well known that citrus leaves do not tolerate wide fluctuations in temperature like this and that this can cause them to drop.
In the North, you do not really have "cold spells", it's more of just a colder season. Once it gets cold, it does not warm up again. The leaves can stay in a state of dormancy without being woken up.

That is what I would think.