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)"