Freezing apple scionwood

applenut_gwApril 6, 2013

I know it has been considered taboo, but I've frozen my scionwood now for a couple years and it works out fine most of the time. Anna and Dorsett Golden didn't survive, but they never really go dormant and usually consists of exclusively fruit buds. But higher-chill varieties do OK, especially if the wood is hard dormant when I cut it and consists of leaf buds.

I use an older dormatory refrigerator that I turn up to "8" and it stays about 28 degrees; newer refrigerators won't do this and freezers get too cold. I've tried putting the wood in plastic bags filled with water, in wet sawdust, and just in a bag with a little bit of water in it, and they all seem to do OK. The buds that are killed are brown or black inside when sliced in half.

Since I have to cut my scionwood in January and do a lot of grafting in April into May, this has kept the scionwood in much better shape that that which was just refrigerated until then. I first heard of the technique from the ARS Germplasm Repository in Geneva, where they regularly freeze scionwood in a grape tote of sawdust soaked with water first.

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I have always been curious about this, as the varieties I am working with are regularly seeing sub zero out on the trees. I had assumed it might be a concern of "freeze drying", but that seems easily overcome by encasing in ice or damp material as you suggest.
Sometimes if we get a late spring the stuff in the fridge is waking up more than I want it to.

I know that I have received scionwood that froze overnight in the mailbox...down to low 20' grafted fine but was not stored at those temps.

    Bookmark   April 6, 2013 at 11:00AM
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You would think that if damage would occur, it would occur right away and further storage at those temps wouldn't matter much. Once the cell walls are ruptured, the damage would be done.

I guess the key is to have fully dormant scionwood to begin with, just as it is with surviving hard freezes on the tree.

    Bookmark   April 6, 2013 at 11:05AM
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alan haigh

As is exemplified by freezer burn of meats, the issue is that freezing can draw moisture from the scions. It is a gradual problem and avoided with meats by wrapping tightly so moisture can't leave tissue. Same thing accomplished, I guess, with apple nuts methods.

I've not had a problem with refrigerated scions leafing out prematurely if I keep them cool enough and by tightly rapping them with stretch plastic and double bagging over that (with a moist rag in final bag) they come out just fine.

    Bookmark   April 6, 2013 at 1:20PM
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fruitnut Z7 4500ft SW TX

28F isn't going to be any different than 32F. The issue is that most refrigerators don't stay in the 32-34F range that would be best. At 40F lots of stuff starts pushing faster than one might think.

I guess ideal would be as little above freezing as possible. This would avoid moisture migration and keep scions dormant.

This post was edited by fruitnut on Sat, Apr 6, 13 at 13:47

    Bookmark   April 6, 2013 at 1:37PM
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Konrad___far_north(3..just outside of Edmonton)

Yes..above freezing is best and you can store them in the fridge for several month.
It sounds like you make them too wet, ..this would encourage leafing out.

We often make the mistake of storing scion wood too wet.
Only modest moisture is required, a moist paper towel,..not wet.

    Bookmark   April 6, 2013 at 2:08PM
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franktank232(z5 WI)

I have a small chest freezer i can set at about any temp i want with an external t-stat...might be something to try if you need to store a bunch. I've used it to store apples at just above freezing.

    Bookmark   April 6, 2013 at 2:19PM
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olpea(zone 6 KS)

Very interesting topic Applenut.

I've always had problems storing scionwood. It always wants to break bud in the fridge before the opportune time to graft. I've tried everything. Running the refrigerator lower, placing the scions in water tight plastic bags and putting the bags inside a 1/2 gallon jug of water before putting in the refrigerator, but nothing worked.

Last summer I bought an old "dorm" fridge at a garage sale for 25 bucks. I have some peach and apple scionwood in there now. I had heard people having success storing scionwood for a long time at barely freezing temps so I'm running the dorm fridge at 30F.

I wonder if freezer burn occurs a lot faster with sub-zero temps (like in a deep freeze) vs. temps at 30F?

If storing at 30F burns the wood, I'll try storing at 32-34F, as Fruitnut suggests. I think this little fridge runs more consistent temps than the one we keep our food in.

    Bookmark   April 6, 2013 at 7:53PM
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alan haigh

I think it may also help if you keep your scion fridge in a cool place- mines in the basement which is almost like a root cellar so it reduces the relative flux in temps.

I bought the kind of thermometer Frank mentions- used for making beer. I didn't find that it allowed to set that precise of a temp- there's a several degree fluctuation between turning off power and turning on to protect the motor of the freezer,I guess. It would have to turn on and off almost constantly to be precise.

Fruitnut, I somehow forgot that you didn't completely freeze the wood between reading and writing- that has been discussed here as well.

    Bookmark   April 7, 2013 at 7:33AM
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28 degrees will freeze water but I bet the moisture in the tree wood does not freeze at that temperature.

    Bookmark   April 8, 2013 at 2:40PM
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to add to murky's point, I'll bet that if you actually 'froze' them at 0F or lower in the freezer, that the results would not be desirable.

    Bookmark   April 8, 2013 at 4:42PM
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olpea(zone 6 KS)

Just wanted to update my experience for this thread.

I collected some scionwood in Feb. and put it in the refrigerator turned down to 30F.

Took some wood out today graft with it and it was pretty dried out. Even the wet paper towels in the bag were freeze dried. I went ahead and grafted with the wood, but I'm not expecting much.

I won't be freezing scionwood any more.

    Bookmark   April 28, 2013 at 9:05PM
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What don't you just freeze them in water? Scion popsicles!!!
Wouldn't that eliminate the fear of the wood drying out?

Carla in Sac

    Bookmark   April 29, 2013 at 3:40PM
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I did that with a batch Carla; I'm giving them about another month before thawing them out to see how they did.

I envisioned milk cartons full of scionwood frozen into blocks that stack neatly. I want to try the same with bundles of rootstock.

    Bookmark   April 29, 2013 at 9:26PM
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Along the lines of what Lucky was saying, I think there's probably an important distinction between the freezing temperature of pure water and "actual freezing." I'm not sure what "actual freezing" would mean for scions, but I assume there are parallels to things like harvested fruit or meat. I believe the large-scale nitrogen-filled storage facilities for apples (and I think pears, too) are kept just below 32 degrees, because the sugars in fruit prevent apples, etc. from actually freezing until temperatures get 2 or 3 - I'm just throwing out a guess here - degrees colder. I know meat is similar, even though sugars aren't at play. If you put ice bottles in a cooler with hard frozen meat, you'll notice the meat will thaw before the ice will. The freezing temperature of meat I think is around 28 degrees. So if you wanted to optimize the storage life of meat WITHOUT freezing it, you'd keep it at 29 degrees. There must be something similar with scions.

I also wonder why scions couldn't be stored at temperatures as cold as they'll withstand on the tree. In other words, if a piece of a tree is fully hardy to -10F on the tree, what changes when you cut it off? I'm assuming something must be different. Does it just have to do with moisture migration (as with freezer burn)? Or are cell walls getting ruptured as when you freeze strawberries and thaw them and their texture is nothing like it was fresh?

Harvestman, to your concerns about the fluctuations that a thermostatic control like that would allow, I don't think it would be hard to buffer those fluctuations to effectively make them disappear. One idea I'd have for a buffer would be a contained salt solution (obviously you wouldn't want any salt contacting the scions) that would freeze-thaw at the desired temperature -- there are charts to easily figure out how much salt will drop the freezing temperature of how much water how far -- but sand or sawdust or anything would work so long as the fluctuations in the temperature around the thermostat probe didn't penetrate the insulating/buffering material faster than the on-off cycles.

    Bookmark   April 30, 2013 at 7:37AM
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applenut said:

"But higher-chill varieties do OK, especially if the wood is hard dormant when I cut it and consists of leaf buds. "


How do you differentiate flower buds from leaf buds?

    Bookmark   April 30, 2013 at 8:47PM
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The flower buds are big and fat, while the leaf buds are much flatter and triangle-shaped.

    Bookmark   April 30, 2013 at 8:53PM
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I would think you could vacuum seal most wood, as long as it hasnt started to break dormancy. This year I got some wood and just buried it in a snowbank in a shaded area for a few weeks, till I was ready to graft. Long term storage I would think freezing hardy wood would be better than leaving in the fridge...

    Bookmark   May 1, 2013 at 9:52AM
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