Spring-pruning and Frost Protection

Hi folks,

Long time viewer, first time forum user here.
I was recently watching the stream on deciduous leafless design and at about 1h23min Ryan responds to a question something along the lines of: pruning a tree in before bud-break messes with the distribution of sugars and starches, which reduces its hardiness to frost - essentially meaning: pruned tree needs to be moved indoors or need to be protected during nights that have frost.
During the last 6-9 months I just kept my trees alive as I was busy otherwise. When Ryan answered the question I was really confused. I read and watched a lot on bonsai before my short break but that answer came as a surprise.
Protecting repotted trees for sure, but pruned ones was new to me.
Can someone confirm and elaborate on the details (or hit me up with a resource I can dive into)?
Thanks in advance!

I think there is a lot of nuance to unpack in this statement.

“pruning a tree in before bud-break messes with the distribution of sugars and starches, which reduces its hardiness to frost” = True

“pruned tree needs to be moved indoors or need to be protected during nights that have frost” = not necessarily true

Pruning requires wound healing which uses some of the trees stored energy. So it is objectively true that the frost hardiness is “reduced”. But reduced by how much? and how many degrees of temperature change does that affect?

Those are hard questions to answer. I think ultimately it comes down to many factors: species of tree, health of the tree, how much was pruned, etc.

If you have a very hardy japanese maple and prune it slightly, the trees stored sugars will be “reduced”, but it’s still going to be much more hardy than a pomegranate and doesn’t necessarily need to be protected if the temps hit 31F just because it was pruned.

I think the other concern is die back of the branch since the tree will be using some of its sugars and starches near the wound to heal the wound and will therefore not be as frost tolerant. But as @bentleythekid indicated it will depend upon the species, amount of pruning, and temperature.

That is also a good point. It is not clear to me how quickly or completely the stored sugars are able to redistribute after pruning. So would pruning a large branch reduce sugar % in the entire tree very slightly? Or the remaining part of that branch significantly, but the rest of the tree not at all?

I was thinking in terms of the smaller branches for a couple of weeks or so depending upon the temperature that it will take for the tree to compartmentalize the wound. I am guess that would utilize the resources from the branch within a couple of centimeters of the wound.

For a bigger wound I am not sure how long a stretch of branch would be using resources to heal the wound. I can see arguments for a similar length, a short length, and a longer length - particularly the tree bleeds sap. I think the safe thing to do would be to leave a nice long stub that can be cut back later.

Thanks to both of you @MartyWeiser @bentleythekid !
I think one point that confused me was how short the answer was. Most of the time Ryan has so much knowledge to shell out that I have a hard time following :wink:
I was definitely thinking of just pruning a tree that reduces tolerance. Major cut back of one or more big branches seemed obvious, as I would remove lots of mass from the tree. But cleaning up a tree, removing bottom growth, reducing back to two branches and cutting elongated ones back never occurred to me as dangerous. Based on your answers I am a little relieved that my feeling wasn’t totally off. I would have pruned trees that were healthy and growing strong last season.
The one or two that had bigger branches removed will be protected.

One direct reply to this, forgot that in my other post. Somewhere in the BSOP Streams there is some info on how trees behave when pruned or get big branches removed I believe.
From what i remember, the tree tries to level out sugars and starches within the whole system. So one big branch removed affects the whole tree. Must have been one of the winter streams, preparation or care I think.