It depends on the species and variety.

I've grafted some selections of fruiting trees - like mulberries and pecans - from the zone 7/8 region to my zone 6 setting with good success, but have had some that couldn't take my KY winters - or I didn't have a long enough growing season with sufficient heat units to ripen/mature their fruits/nuts.
Many of the common fruit varieties, like apples, pears, stonefruits, etc. will grow and fruit over a wide range of climatic conditions/regions, but some perform better in others.

you go by the zone rating of the scion ... not the understock ...

as a wild example .... you can not take a tropical mango .. and graft it onto some z4 long lost relative.. and think you will get mangos in the great white north .... on the theory that the roots will survive winter .... the bud will be long gone as soon as the temps start falling ...

now.. if you are talking one zone.. a little zone pushing ... and you have some special little zone pushing nook in your yard ... a micro climate as we say .... yes.. it can be done ...

make sense..

never apologize for a question ... the only bad question is the un-asked question.. IMHO ...

ken

Another old post I dug up while bored.

Rootstock can definitely effect the hardiness of a tree. Many fruit-tree rootstocks are chosen for their ability to increase hardiness. Diospyros virginiana used as a rootstock for less-hardy oriental persimmons comes to mind as an example. A key feature of some apple rootstocks is an ability to increase hardiness. Also, keep in mind that hardiness is not always as simple as the lowest temperature a tree can survive. Things like soil moisture during colder periods can also effect hardiness. If one rootstock is able to survive a wet, cold winter better than than a tree's natural root system (or another rootstock), then hardiness my be improved by its use.

As Lucky already said, results depend on the species and even cultivar, so this information is all hypothetical without specifics.

Off the top of my head, I can't think of any instance where a rootstock provides more hardiness to the grafted scion variety. They may exist, I just can't think of one.
Some rootstocks are more winter-hardy than others - for instance, when you get into zone 4 and colder, a 'standard' rootstock may be necessary for most apple varieties, as the dwarfing and some semidwarfing stocks may not be tough enough to withstand the winters.
But I'm not certain that anyone has shown that any give apple variety, grafted onto, say, Ranetka or Antonov, is made any more winter-hardy just by virtue of being on a cold-hardy seedling understock

Besides the persimmon example, lots of other types of trees are grafted to improve hardiness. The use of Poncirus trifoliata on citrus is another example. I attended a talk a few years ago that gave numerous conifer examples (although I don't have the info easily available right now). The guy was showing us trees planted and growing in places where they normally stood next to no chance of survival. If I get time, I'll try to post more info.

The apple example may not be the best example (for a couple of different reasons). Many cultivars are not grown on their own roots (cuttings and even layering isn't always practical), and the hardiness improvement (if any) may be due only to their increased ability to deal with wet soil in winter (which, BTW, would still be improving their hardiness). I'll just "chunk" the apple example.

I'm not convinced that D.virginiana understock confers any additional winter hardiness to D.kaki selections grafted onto them. 'High-working'(grafting 5-6 ft or more above ground level) probably does more, but some kakis will still 'wake up dead' the next spring.

P.trifoliata...maybe. Mainly used to confer dwarfing to citrus. Might provide some ability to survive all the way up into lower zone 8 - but sure won't provide enough hardiness for a good fruiting citrus selection to survive in-ground outdoors in zone 6, although Poncirus is fully winter-hardy here, and at least as far north as Cincinnati, OH.

"In the eastern United States, (Diospyros kaki) are grafted onto the native American persimmon, D. virginiana. This rootstock significantly contributes to cold-resistance." - Fruits of Warm Climates by J. Morton

Similar quotes can be found through persimmon literature.
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"Commercially many citrus varieties are grown on Poncirus rootstocks, which provide resistance to some diseases, increased cold-hardiness and high quality fruit." - www.homecitrusgrowers.co.uk

"(Poncirus trifoliatahas) the potential to survive low temperatures and, when used as a rootstock, can impart some freeze hardiness to scion trees grafted onto it." - U of Fl. Ext. Service

A quick google search will turn up numerous such statements.
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More generally: "Grafting can increase the winter hardiness of certain plants by providing them with a root system that is more tolerant of low temperatures." - Ornamental Horticulture: Science, Operations & Management by Jack E. Ingels
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Not sure what your point was about fruiting citrus survival in zone 6 (which was not previously claimed or even mentioned). Obviously I don't expect to see palm trees in the arctic (at least not as a result of grafting).

Diospyros virginiana and Poncirus trifoliata are universal understocks for their respective genera and rightly so. First consider the availability of seed, those of who are propagators know how important this is. I mean commercial quantities. These species are readily available and produce predictably reliable understock. These seedlings are tough and not bothered by the winter.
Does a fruiting orange, grafted onto P. trifoliata have any additional winter hardiness? I kinda doubt it. Instead P. trifoliata is used for dwarfing and nematode resistance. Think for a moment, which part of the grafted tree is exposed to the elements, certainly not the rootstock. The TOP is damaged by the cold, not the roots.

Re: Palm in arctic:

I didn't mean for that sentence to sound like it does. I was saying it kind of joking, but it didn't come out that way. Sorry.
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Sam, What do you base your contrarian viewpoint? The industry seems to universally disagree with you, from what I have seen.

P.S.

"Diospyros virginiana and Poncirus trifoliata are universal understocks for their respective genera and rightly so."

Unless I misunderstand what you are saying, this statement isn't true at all.

I don't believe Sam is contrarian, but rather, realistic.
My own experiences suggest that claims of increased winter-hardiness are merely anecdotal, with no more validity based upon statistical evidence than my own allegation that it's not the case.

Just because an old saw may be repeated, repeatedly, by a published author or university professor, it's not necessarily so.
For instance: anthropogenic global warming.

Here is a link that might be useful: Abandoning AGW pseudoscience fraud

Well you certainly have a point there Lucky. It's like those crazy people that still believe the world is round, or egg-shapped, or whatever. I can clearly see it's flat just by looking outside. When will people start believing what they can plainly see and stop believing all those university professors? Ya know, if those professor type people knew anything about anything, they'd be out "doing it" instead of "teaching it". 'Least that's what I hear a lot. And, of course, just because an industry goes out of it's way to do things a certain way, that seems to most everyone to be working, doesn't mean they have any idea what they are doing. They are probably just guessing, listening to the crazy scientist, or maybe one of those silly professors told them to do it that way. The perceived benefits are probably just a big mirage. You are probably right after all.

guys here is the picture of my 2 newly brought grafted mango tree . can u guys identify what kind of grafting is this?
will it bear fruit early. i bought it 4m a man who too don't know what variety and kind of grafting is that.
plz help!
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guys here is another one of my guava tree. which is i dont know may be air layered grafted. u can see 1 tiny flower bud too. plz guide me whether its a air layered guava.
thanz!

img src=" {{gwi:403326}}">

Karbas,

I can't see what your posts have to do with the topic of this thread. Why don't you start your own thread so that the original poster doesn't get responses meant for you AND so that the thread doesn't contain multiple, almost unrelated, topics?

The trees in your first picture look pretty rough, and, if they look as bad in real life as they do in the picture, I'd call the type of grafting...poor.

I don't know what you mean in the second post by "air layered grafted". Air layering is a technique use in place of grafting.

Looks like some sort of 'approach grafting' technique.