Why can't apple scions freeze while apple branches on trees can?

Hello,  

Almost every thing that I read about apple scion storage says that they should be stored somewhere close to 34 degrees Fahrenheit and that they will be ruined if they drop below freezing.  I was wondering what changes that makes a scion in a refrigerator different than a branch on a tree?  Apple trees obviously endure much colder temperatures without harm.  In fact, I think that they need colder temperatures (maybe).  Does it have something to do with sap circulation?  I've always wondered about this but never seemed to take the time to ask.

Thank you for any replies,
Tim

Pruning is known to affect the cold hardiness of the tree (https://extension.psu.edu/tree-fruit-cold-hardiness-pruning-effects) so perhaps the same mechanism also affects the scion that is cut off the tree.

My suggestion would be that a tree has roots that go way underground to prevent the free from freezing which a scion does not have.

Tim Mackson wrote:Hello,  

Almost every thing that I read about apple scion storage says that they should be stored somewhere close to 34 degrees Fahrenheit and that they will be ruined if they drop below freezing.  I was wondering what changes that makes a scion in a refrigerator different than a branch on a tree?  Apple trees obviously endure much colder temperatures without harm.  In fact, I think that they need colder temperatures (maybe).  Does it have something to do with sap circulation?  I've always wondered about this but never seemed to take the time to ask.

Thank you for any replies,
Tim

I don't know if that is true.

I have forgotten about buckets of left over scions left outside that went through many freeze-thaw cycles that I later found a use for, as far as I know they had about the same success rate as ones I took care of.

A few weeks ago I was talking to a grower that sells a lot of scion wood, and he was saying that scion can dip down into freezing for a short time and be fine and that he ships all of his scions while the weather is still freezing to most locations.

It would be interesting to see how long it could tolerate being at freezing without damage, and I bet that mild freezing would probably be okay for a pretty long time.

I was reading an old Southern apple tree book recently,  and it was talking about how before the days of refrigeration they would bury the scion wood in a little sawdust or leaves outside and uncover them at grafting time. In colder areas I bet they could be buried in a sandy well draining spot and then mulched with leaves to help to moderate the temperature in a similar way.

Best of luck with your scion Tim!

Steve

I also suspect that the "don't freeze scions" advice is actually more based on "don't put scions in the freezer." While zone 4 is going to have occasional lows below what is found in a freezer, it's generally not going to stay below -10F for a long period of time. Also, putting scion in the freezer is going to drop the temperature much more rapidly then would typically happen outside.

My family traditions in fruit tree grafting are from East Anglia, England.  The traditions date to way before the late 1800s, but that's when my great-grandfather learned, and most of what follows comes through him (and his brother the Plesher - guy who makes and maintains hedgerows).  Note this is traditional oral wisdom, not modern grafting ideas.  It's also specific to that climate - which was far more severe than it is today due to it being the end of the last mini-ice age.  

First, it was sacrilege to cut a tree if there was a likelihood of frost.  Cutting the tree in winter causes enough risk as the tree is dormant and is slow to heal the wound.  Cutting the tree and having a freeze within a couple of days greatly increases the chance of die back or infection entering the wound/cut.

The fruit trees were pruned in late fall or early winter after the barley was in and the kitchen garden put to bed (weather dependent).  Several branches from the pruning were kept for grafting and these were placed with their butt in the soil like a cutting in the shade of the tree.  

When grafting season came, these sticks were taken from the ground and used for the scions.  

When I read modern books about grafting, they say this idea is bad because the scions will get damaged.  Maybe in different climates, they do.  All I know is it works for us.  The branches freeze during the winter, but not for the first few days (because we don't prune if there is a risk of frost) and somehow acting like a cutting keeps it as living tissue which is more resistant to frost damage than recently cut tissue (think kale that can withstand a frost, but will go mushy when harvested frozen).

To answer the question more directly,  we avoid the freshly cut branches freezing both on the tree and scion until they have a chance to recover.