grafting onto hardy orange and grafting onto pawpaw zone 6 pennsylvania

I live in zone 6 Pennsylvania.  I have some young pawpaws and some young hardy oranges.

Is there any other type of edible citrus that I could graft onto the hardy orange that would make sense in my zone?  Same with pawpaw.  If I grafted on a relative, the scion would just die in the winter, so is there a point to that?

If these trees stay outside in the ground over winter in PA, won't the scions be too tender and freeze/die?

My understanding is Hardy Orange is often used as rootstock for citrus for its cold hardiness.  What I wonder is, what is the point if the scion can not take the cold.  There may be something I don't understand.  What is it?

Any suggestions that would work?
Steve

I've never ever heard of a pawpaw relative.
I would be glad to have some hardy orange,  the juice is good to me, even though there isn't much of it.
I've tried to start cuttings with no luck.

Hardy orange might  just be tough,  period  and as such, a good candidate for rootstock.
Resistance to disease,  great root structure and dwarfing are the reasons Ive heard for using root stock.

I’m in Zone 6b but it was Zone 5 a few years ago.  I’ve been wanting a citrus for a long time. Finally planted the hardy but not vary edible variety this year. I read somewhere that some wild trees had much better fruit. I wish someone would find or develop an improved variety.

This company has some interesting trees. http://mckenzie-farms.com/photo.htm

I haven’t wante to risk the time and money yet. I’m running out of projects higher on my priority list, so maybe I will try a tree  or two next year.  

If you decide to do it his year, I’d get them planted right away so that they can get established before winter.

Steve Horst wrote:
If these trees stay outside in the ground over winter in PA, won't the scions be too tender and freeze/die?

My understanding is Hardy Orange is often used as rootstock for citrus for its cold hardiness.  What I wonder is, what is the point if the scion can not take the cold.  There may be something I don't understand.  What is it?

I am assuming by Hardy Orange you are referring to the trifoliate orange, aka Poncirus trifoliata.  It turns out there are many reasons that Poncirus is used as root stock for "better" citrus varieties, of which cold hardiness is just one.  Before I get into the others, though, it's my understanding that having cold-hardy root stock tends to confer a couple (perhaps a few?) degrees of cold hardiness onto whatever citrus you've grafted onto the root stock.  How much good this does you all the way up in Pennsylvania is another question.  I am in 7(b) here in central Oklahoma and have made quite a study of cold-hardy citrus, but I haven't found any yet that I am confident will survive and produce without full greenhouse-style protection.  Even getting the Trifoliate trees through their tender seedling phase and fully established has proven tricky for me, although I have several very well-established adult trees in the area to prove it can be done.  We tend to get a few days of cold dry harsh winds every winter that just aren't citrus friendly!

So.  In addition to cold-hardiness, it turns out that the various improved citrus varieties often grow rather differently (sometimes better!) on Poncirus root stock.  This can, for example, include dwarfing tendencies that might make it easier to build temporary seasonal protection around the trees.  Here's an ancient USDA circular I found about Satsuma mandarins that contains a bunch of interesting info about using Poncirus root stock, with a money quote that may be useful:

There are very few varieties of citrus fruits that do not succeed on the Trifoliate stock, provided, always, the soil is adapted to the stock. Some varieties succeed better on this stock than on any other. Perhaps the most striking example of this is the kumquat, which is the hardiest of the evergreen citrus fruits. On Trifoliate stock it bears heavy crops of fruit while still a mere bush.

Another variety of citrus fruits that behaves very differently on the various stocks is the Satsuma, a very early orange of the mandarin class introduced from Japan, where it is known as the Unshiu. This variety, which is the earliest and at the same time one of the hardiest of the oranges, grows very well on sweet-orange stock — better, in fact, than on the Trifoliate orange on most soils — but the fruit is of decidedly inferior quality on the former stock, being coarse, dry, and insipid, besides ripening later than on the Trifoliate stock.

On the other hand, the Satsuma budded on the Trifoliate orange produces fruits which ripen early and are of excellent quality, smooth skinned, firm, and juicy. The trees budded on this stock are smaller than those budded on sweet-orange stock, but they bear earlier and fruit more profusely. They also ripen their fruits earlier in the season and are decidedly hardier.

There are several threads on Permies about cold-hardy citrus research that Permies members have done.  The most promising appear to be kumquat, calamondin, yuzu, and a bunch of rare and hard to find hybrids and crosses that involve these and Poncirus in various degrees.  But, at the end of the day, even if you get a tree that can survive your winters, getting a tasty fruit with a growth habit that doesn't have it hanging out on the tree during the coldest winter months is a genetic challenge.    I haven't given up, but so far all I've done is work on getting my Poncirus trees established.

Steve, in Pennsylvania P. trifoliata is reliably hardy in the southeast, but not as much in the north. Any scion grafted on to P. trifoliata for outdoor survival w/o protection needs to be nearly as hardy as P. trifoliata itself. The hardiest Citrus relative short of pure Poncirus are advanced hybrids between Poncirus and various other Citrus species. There are amateur Citrus breeders in both Eastern and Western Europe. There are cultivars surviving in Switzerland, France and Germany. There are a few amateur Citrus breeders in the US in Kansas, Virginia tidewater area and Pennsylvania among others. In a Pennsylvania test, a few specimens have survived -11.8 deg F with cold damage, but some stem tissue remaining alive. This test involved F2 citranges (hybrid between Poncirus and blood sweet orange). These are new selections and haven't been grown to fruiting. Fruit characteristics may be quite disappointing.

You are correct in thinking tender scions on Poncirus will fail in very low temperatures. Poncirus does provide a bit of additional protection to tender scions, but the protection is not very great.

@Herman, thanks for your message. Do you have some more info on the

cultivars surviving in Switzerland, France and Germany.

As well as on the amateur Citrus breeders?

A few breeders off the top of my head: Bernard Voss in Germany, Ilya B. in Paris, France. Cultivars: Curafora, Venasca, 5* citrumelo, US 119. Sources: Bernard Voss Germany, Eisenhut (Switzerland), and Adavo (Czech Republic.

Thanks. Here the links I could find.

Bernhard Voss, Germany
http://agrumi-voss.de/

Ilya B, France ??
Could not find it.

Eisenhut Switzerland
https://eisenhut.ch/pflanzenmenue/index.php?q=citrus&id=285300&gruppe=&orderby=abc&modus=bilder

Adavo, Czech Republic
https://eshop.rakytnik.com/katalog/zbozi/citrusy

Ilya is a cold hardy citrus breeder active on TropicalFruitForum. He is not a source for plants, rather he is breeding and selecting edible hardy citrus and has created new hybrids he is evaluating. With his scientific background, he is quite knowledgeable concerning Citrus genetics.