Cold hardiness of grafted trees

Newer grower here. I’m planting an orchard of native trees here in Zone 6. I was hoping I could graft some more tropical trees onto the native rootstocks. What are the limits of frost resistance for grafted trees? It might get to around -15F here in the worst winters.

Some examples of what I’d like to potentially graft:

Asian persimmons (Diospyros kaki) onto American persimmon (Diospyros virginiana)

Black mulberry (Morus nigra) onto red mulberry (Morus rubra)

Peaches (Prunus persica) onto wild plum (Prunus americana)

Will the grafted portion freeze off in the worst winters? The most work I’d like to do to protect them is just basic mulching.

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from what i understood, generally the stock has little to do with the (mid) winter frost hardiness.

So if peaches freeze where you are, grafting them on plum will likely do little to help them.

The wood/buds above the graft union might have to low a frost tolerance.

Usually in cold area’s you graft low. And bury the graft union under mulch. That way in an especially bad winter. The top of the tree might die off, but it can regrow from the grafted variety.

I once saw something about figs being grown in spot where winter was really harsh. I think they dug ditches, planted the figs in there. Trained 2 low horizontal branches, of which they let vertical shoots grow. (UFO cherry or Guyot grape style). They buried the horizontal part each winter. So even if the top part of the tree died, they still had most of the “framework” alive. And plenty of new growing and fruiting shoots.

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@oscar is right, the scion’s hardiness is what you need to worry about. Peaches should have no trouble where you are, but Morus nigra and most (if not all) Asian persimmons don’t stand a chance.

However, both of those should work well in large containers, just shuffled into the garage over the winter.

Morus Nigra will not survive in your climate.

Like others said, the hardy rootstocks will be fine. The growth from scionwood is another story.

Look like you are in zone 6a, borderline 5b. So far, no pure Asian persimmons can survive zone 5. I am in zone 6a, they don’t survive here without protection, either. The hybrid like JT - 2 appears to survive zone 6 well.

Peaches- it depends on varieties. The leave buds are likely to survive our zone but flower buds are more tender and could easily be frozen out. You need to pick varieties with flower bud hardiness like Madison, Reliance, PF24C, etc.

And then there is the fact that in a bunch of species the buds from where flowers are supposed to come in the spring are less winter hardy than the rest of the tree; you can nail that perfect balance where the tree survives every winter but the flower buds don’t, so you end up with a tree that may never set fruit.

If you can hit -15f in a bad winter you are not in zone 6 and should not be planting as if it was. Trees are meant to last a very long time; when selecting them for hardiness you don’t go by the average, you go by the worst possible year. We (and for all I know everybody else) call them test years, and they are what determine if a given tree is truly hardy enough for your area. Reading some of the early attempts at developing cold hardy apples seems to have a very common ending; the trees were looking very promising until such and such test year came and of the 20% that survived most came out with 50%+ winter kill. But guess what? Those 3 over there? They did good, put an ‘approved’ label on them, they made it.

Old timers remember the winter of 1989 were a confluence of factors pushed the temperatures waaaay down. And I’m talking waaaay down by Alaska standards. The state record held since the test year of '77 came close to be broken but it missed it by a degree, hitting 76 degrees below zero in Tanana. The rest of Alaska coped with extremes they’d only read about in Jack London novels: Thirty below zero in Anchorage, Homer chilled at minus 24 degrees, balmy Juneau hitting minus 3 degrees; and Fairbanks trucked along at 51 below. Well it didn’t deforested Alaska and I’m pretty sure plenty a Dolgo and Parkland apple trees woke up in the spring as if nothing had happen.

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That’s not exactly how the USDA zones work. Maybe their maps are misnamed or just ridiculous. Over 30 years, let’s say you average an annual minimum extreme low of 11F years each year except one which gets down to -15F. You would have an average annual minimum low temp of 10.1F and be in USDA zone 8a. Possible? Maybe not. Purely hypothetical, but it’s about risk tolerance. If you want to grow something that might get fried with a one time low of -15F that happens once every 10 or 20 or 30 years or so, maybe you risk it. But, maybe that low happens next year. I’ve done a few borderline plants over the years just for the halibut, but my patience for that is generally low. I think there has been some discussion on here that the USDA zone maps should be called something else…or maybe it should be calculated a different way. Or, perhaps for each location, it should give your yearly odds of hitting certain low temps. The data is in a pile somewhere but not presented in any meaningful way.

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I am in zone 6 and my coldest winter produce 3 nights in a row -19F, -24F, -25F, 1977

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snowflake, it may be the approach we take up here but any tree that up and dies the first test winter is simply not hardy regardless of what the USDA zone map may want to say about it, or what the vendor may tell you it is good for. Zone information alone is often not adequate for predicting winter survival but if you tell me that on your particular neck of the woods it is not uncommon to hit -15f, for picking say apple trees I would not call ‘hardy to zone 6’ hardy enough.

50 years or so ago nobody thought apples could grow in Fairbanks. Clair Lammers and other growers set out to prove that wrong and now there are well over a hundred varieties that are hardy up there, with a bunch more varieties that are hardy to my balmier neck of the woods. I do have a few things I’m testing for hardiness but (for example) the bulk of my apple trees (9 and counting) are hardy to zone 2 and 3. They are the performers that have proven workhorses around my so-called zone 4 that keeps killing zone 4 trees.

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With you being zone 6a and getting in the mid teens minus, I would only recommend JT-02 hybrid, and others tgat may work maybe Kasandra, Rosseyanka, Davids Kandy, but the best thing is to graft your rootstock resl low near the soil and then protect the bottom foot+ for 3 years so it can gain mass/thickness/hardiness.
Another thing worth trying if you are not in a mudhole, is graft low, then transplant deeply plant graft 6" deep, or mound soil up above graft 6", my nikitas gift would be dead if I had planted with the graft union above soil line here in a protected spot in 6b.
Dont waste your time on asians, or non-hardy hybrids like Nikita, 6a is too cold for the best. Check the post I did titled “Persimmon Cold Hardiness Resource”.
Plant good earlier ripening large American persimmon, like Prok, Early Golden, H63A, H118.
Peaches, plant those that produce even in a late freeze, like Early Redhaven, Garnet Beauty, Madison, PF24C etc

What I do with young trees is to burry the graft in the fall, dig it up in the spring. Same thing for grapes; they are safer underground in case we get a cold snap without adequate snow coverage.

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I would agree with that. The zone info is generally next to worthless in areas where the temp varies even a little bit. It factors in almost nothing. Winter swings or anything like that. I’m just saying that the “zones” as they are defined having nothing to do with one extreme event. So, he may be a zone 6 or 5 or 8 or 9 or whatever based on the USDA zone definition and not get a good picture of whether a plant will fry or not during the winter. Even looking at the record low temp doesn’t paint the full picture depending on the plant experiences an 80 or 90 degree temp drop in a few hours (at some time of the year).

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Not the thread for this thought I guess, but I’ve seen Prok slow to harden off in the fall and wondered if it could be more prone to winter injury. I experienced some of that this year but it could be related to other factors other than the -29F (or worse) that hit them.

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@snowflake The cold weather getting 15F temps etc before trees harden can be real damaging. I had it happen to a young yates american and lots of mulberry so it can happen to anything especially young trees. Young hybrid persimmons need protection for 2 or 3 years to acclimate.
Peach pear apple and many other things do a lot better on not being prone to this.
-29F can harm hardened trees too though, especially young ones and any hybrids even the hardiest, probably most americans can get damaged too depending on conditions.

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@PaulinKansas6b Prok seemed uniformly injured on multiple young trees 6-9’ tall. The smallest one died completely above the graft. There was another variety that suffered similarly. Maybe h118…but I would have to look. The same size WS8-10 in the same areas had no issues. Some others were ok too…but I haven’t taken a tally.

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Honestly I agree that growing in pots and bringing them inside the garage is your best bet. I am zone 5 and was able to over winter a Morus Nigra. The thing that did them in was not the cold but me yanking them because I did not like the taste of mulberries and my throat got scratchy after eating them. Not sure about persimmons. Most peaches should easily survive zone 6 or higher. Improved Alberta is hardy to zone 5 and so is Redhaven. Genetic dwarf peaches and nectarines are hardy to zone 6 which is your zone assuming you are zone 6. I question your zone though because we have not had a -10 in years where I live and we are zone 5 which is supposed to get to -20.

Oh ok. Yeah it would be interesting to take notes like that for several damaging years over a period of time and see what they look like. For me, each year is so different. But if Prok does consistently prove a more prone cultivar it will get lower on my list. I have 2 young grafts of it. So I will keep your experience in mind. If you have similar results over the coming years it would be of value to us all if you kept notes and share them. Thanks! :slight_smile:

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@PaulinKansas6b I will try to put together some notes! Been fighting a lot of things and it hasn’t bubbled to the top of the priority list :slight_smile: Prok reminded me of Deer Magnet in hardening off late, so I was a little concerned about both of them. We had a really long mild fall so the late hardening didn’t matter in the fall I guess. I can’t recall totally what deer magnet did everywhere this winter, but on a double graft (two trunks) of Deer Magnet and Prok on the same tree, Deer magnet suffered maybe only the slightest minor tip injury (if any, I would need to look), and Prok on the same tree burned back down futher. I shouldn’t say much more until I take more accurate notes on more trees, but I remember that on the one tree.

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Ok well thanks for your feedback! Perhaps over the next few years the picture will become more clear. Lets keep this in mind and share results for all to benefit. :slight_smile:

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There are a few tricks that helps hedge your bets. As I mentioned earlier as soon as the young tree start going dormant burry the graft. Get a bunch of dirt and do a little volcano around it. The graft joint is one of the last parts of the tree to winter harden and if you loose that well the tree is gone. Dirt is a good insulator and this is cheap insurance in case you get hit with an early cold snap with no snow cover.

Another part of the tree that takes longer to harden are sharp forks. It is not well understood but something about the way tissue forms there that slows down winter hardening. Add this to the reasons to avoid those.

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