North American Fruit Explorers mailing list at ibiblio

["Dave Griffin" <griffingardens@earthlink.net>]

Kevin et.al.,
  I recently got a reasonable explanation from Jim Cummins for my related
question posted here last spring, after much inquiry elsewhere wherever I
thought I might get one. I had noticed via the scratch test that there was
green cambium in the twigs of most of my tender stone fruits, even after
-29 F low temp. Cruelly, these apparently healthy trees leafed out but
gradually died over the first month. As the trees declined I began to look
at the cambium in the trunks and found dead tissue in many of the same
trees that even still had bright green cambium in the upper branches. Often
this was in the very lowest part of the trunk just above ground level and
occurred even though the trunks were well protected from SW injury and were
below the snow line for the coldest temps. The explanation from Jim is
that, except for the newest tissue in the growing tips, trees harden off
from the upper branches downward and the last part to harden off is the
trunk. I suppose they can survive this pattern most years because of the
extra insulation of thicker bark and if there is timely snow cover, but
there must be a set of conditions like we had last year where the trunk is
more vulnerable for a time than the twigs. 
  So for me the answer is budding high onto a hardy rootstock to form a
stem builder tree, but not for what doing this might contribute to the
scion hardiness so much as for what it does for the trunk itself - provide
hardiness to what in some years is a vulnerable part of the tree.

Dave
zone 4a 


> [Original Message]
> From: Ed Forest 
> To: <nafex@lists.ibiblio.org>
 > Date: 10/30/04 8:34:47 AM
> Subject: [NAFEX] Rootstocks/dormancy
>
> Correction:
> I had written "Rootstock dormancy patterns seem to have little effect on 
> survival of
> cultivar", I meant to say the "dormancy" of the cultivar with an emphasis
on 
> the word "seem".
> The old question of "imparting" of hardiness of rootstock to scion or
vice 
> versa hasn't really been figured out, I don't believe, and that may be 
> because dormancy and rootstock/scion interactions are complicated. So
even 
> though I don't see outward signs of an effect of the rootstock on the
scion, 
> it may not mean there is no effect.
> Kevin B
> 



> Rootstock dormancy patterns seem to have little effect on survival of 
> cultivar, ie, even though ranetka goes dormant ten days later than 
> antonovka, cultivars on ranetka are able to survive harsher winters.
 
> In short seasons I choose stock that either ripens early or if I want to 
> take a chance, an cultivar that ripens later, but is hardy enough to
endure 
> cold winters without much preparation. Tests have shown that trees that
drop 
> their fruits even a day or two later than others can suffer more winter 
> damage. As soon as those last fruits drop, the tree goes full steam into 
> dormancy. So in a marginally hardy tree late ripening fruits can 
> significantly effect its survival.
 
> Kevin B