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  • From: "Dave Griffin" <griffingardens@earthlink.net>
  • To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>
  • Subject: Re: [NAFEX] Cold Hardiness in Peaches
  • Date: Tue, 3 Jan 2006 06:51:04 -0600

Hello all,
I'm just getting to this and I hope nobody has been waiting for a clear
and satisfying answer to explain the complex question of how resistance to
winter injury works. I'd like to hear such a thing myself but I think we
all wait in vain.
Consistent with the myriad responses - all of them accurate and germane -
we know some of the things that bear on this process but don't have all the
pieces of the puzzle, and especially, I think, we don't have a very good
understanding of how all these things fit together and influence each other
to produce the complex system that allows a tree to survive in a certain
location under winter conditions. It is important to remember that even
mild winter conditions would quickly kill any tree on the planet if they
occurred while that tree was green and growing. Is it any wonder that a
process that can transform a tender growing plant to one that can withstand
extreme winter conditions without injury is a complex one that is not
easily understood?
Why did most of the apricot flower buds and almost all of the peach
flower buds die after only -23 F min last year - even on the -40 varieties
- when they went through -29 F the winter before with little or no damage?
My guess is that it had something to do with a persistent period of cold
(but not severe) weather without snow cover in December that produced deep
frost. In checking this with two other fruit breeders with an overriding
interest in cold hardiness, neither thought that this should make any
difference to flower bud mortality. But even if the conditions that
produced the deep frost didn't directly cause the buds to die, I'm not
ready to agree that it had no influence on the hardiness system in some
indirect way, even though I couldn't begin to say how. To me it is more of
a mystery that some trees are not damaged by extreme cold than it is that
some are damaged. You don't have to stand out in the orchard in -40 weather
for long to appreciate what they have to be able to endure and the complex
system of changes that allows them to do so.
Why weren't the vegetative buds and branch tips on my peaches and
apricots also killed? Why didn't my tender plums and pears have any flower
bud damage whatsoever under these same conditions? Because they are somehow
different. Sorry, but that's the best answer I have. Meanwhile, we can
continue to make educated guesses and to design and construct new methods
to grow tender trees in the hope of stumbling onto a way to provide the
elements missing in their incomplete system of resistance to winter injury.
Most of what we know about hardiness has come from failure, perhaps greater
understanding will come with the implementation of certain horticultural
methods that provide success.

Dave


> [Original Message]
> From: Jim Fruth <jfruth@uslink.net>
> To: <nafex@lists.ibiblio.org>
> Date: 1/2/06 8:38:08 AM
> Subject: [NAFEX] Cold Hardiness in Peaches
>
> Bernie answered why his apple trees die while mine thrive in that his
> climate has a longer sustained low temperature than my climate. Some
months
> ago, Dave Griffin wrote about his zone 3 peach tree experiment having
> noticed that the boles fail to harden off in time for Winter. I see both
> conditions happening in my (zone 3) peach orchard and suspect that, while
> the above two conditions contribute to the demise of some of my trees,
there
> seems to be another, unidentified, factor at play.
> First, to answer Dennis Norton's concern about excessive nitrogen
> applications in Fall, the nitrogen I apply is never excessive - I follow
my
> soil testers recommendations. Secondly, I apply fertilizer ONLY AFTER
> dormancy has occurred. Also, I ALWAYS drastically thin the peach crop
> allowing no two fruits to be closer than 4" apart and not more than 3 per
> branch. Dennis also asked about age; after last Winter's -38° F I've only
> got one tree left that is over five years old. It did get beat up a bit
in
> that upper ends of branches died back. Worth mentioning is that it was
> genetically different from all others in that part of its fruit were
> (typically) borne on spurs whereas fruit on all others were borne only on
> new wood.
> Before last year's big freeze, only some tree deaths could be
attributed
> to non-hardening off. Most often winterkill occurred in the crown among
> branch ends. Sometimes trunk (bole) death occurred (characterized by
Spring
> crown growth that soon withered). Occasionally, trunks would winterkill
> down to the snowline sprouting from below that point the following Spring.
> Whenever trunk death occurred, trees re-sprouted from the roots. About a
> third of the time, though, trees would winterkill(?) and not sprout from
the
> roots.
> So, from my observations, while sustained low temperatures and failure
> to harden off are two factors that contribute to the demise of peach
trees,
> there's got to be one, or more, other factors. What might they be?
> --
>
> Jim Fruth
> Brambleberry Farm
> Pequot Lakes, MN
> www.bberryfarm.com
> Jams, Jellies and Syrups
>
> I have never heard of peach trees withstanding fairly colder temperatures
> than about -12?F; however, hardiness is also affected by the
preconditioning
> the trees receive before being exposed to winter temperatures. How old are
> the trees when they die off?
>
> I know you mentioned hardening off is not a factor, but if the tree is
late
> in going into dormancy it will be more susceptible to cold winter
> temperatures. I notice that you fertilize some of your crops in the fall.
> Excessive levels of nitrogen fertilizers in late summer or fall can delay
> the onset of dormancy and increase the tree's susceptibility to winter
cold
> injury.
>
> If a tree is cropped too heavily, especially in late summer, its reserves
> are depleted and the tree may be susceptible to winter injury. These are
> all factors that may or may not exist in both your and Bernie's situation.
>
> Dennis Norton
> Royal Oak Farm Orchard
>
>
>
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