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nafex - Re: [NAFEX] Cold Hardiness in Peaches

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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 12:17:32 -0600

Hi Chris,
 
Van Well has PF 24C although they may be sold out for 2006. I have 24C here for testing but it is new. PF24-007 is not a hardy peach and is not related to 24C (this is direct from Paul and I have killed it too). His naming (numbering) system goes by ripening season so that 24C and 24-007 ripen in the same season = 24, but are different cultivars (C and 007).
 
There are many ways that winter weather can damage or kill trees here. After deep mid-winter low temperature, the most likely cause of death is early onset of winter with its sudden drop in temperature before trees have had time to acclimate, then Southwest injury. Late spring frost is a problem with apricots as they always bloom too early wherever they are grown, but this is almost never a problem with the later blooming peaches. Root damage can occur when cold comes with a lack of snow cover to ameliorate ground temperatures. The one prime element of cold hardiness that we usually don't have a problem with in this continental climate is de-acclimation due to mid winter warm-ups. When it gets cold here it usually stays cold until spring and that is why pretty much everything blooms within a 2 week period and why there is no appreciable differences between cultivars of the same species. I think this is also why I can grow many zone 5 trees here on the northern border of zone 4. No, there were no mid-winter or late spring warm ups here last year at -23 or the year before at -29, in fact they were very similar winters in every way except for that cold snowless December last year. Most of the apricot and peach flower buds had been long dead by the time that the few remaining ones bloomed, and would not have dropped like rain as I handled them to do crosses if they had been freshly killed. Also, if it was de-hardening why didn't it affect my tender plums and pears the same way? I also grow lots of grape varieties and non of them were damaged. I'm still convinced it was something else and that it is linked to that cold period in December.
 
Dave
 
----- Original Message -----
From:
To: nafex@lists.ibiblio.org
Sent: 1/3/06 10:27:34 AM
Subject: [NAFEX] Cold Hardiness in Peaches

First - For some of the Flamin'Fury and Stellar series Check out Adams County Nursery,
though mainly commercially oriented, they do sell retail (mailorder) to homeowners. 
Nice company.  Will not send peaches for fall planting.  I do not believe they
have P24C (P24-007 they have, but it appears to be different).  You might want
to call them as sometimes their web pages do not reflect their exact inventory.
(After attending NAFEX conference in New Hampshire, wanted the Hampshire apple -
they had it but did not list it completely (was in price list, but not in descriptive
pages)).
 
<<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. >>
Dave, I live in balmy zone 6, but have decided to be insane enough to try to
grow apricots.  I suspect that you lost the buds not to the -23, but to fluctating
temperatures nearer spring:

<<  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.>>
Also, prunus as a genus, usually has its flower buds open before its vegetative
buds, so they will often survive while the flower buds are damaged/killed.  I believe
that each species has a different relative hardiness, and a timing for when they tend
to come out.
 
Also as an aside, I was at a presentation on grapes and cold hardiness.  It is generally
known that vinifera (wine grapes) are not as hardy as lambrusca (Concord).  What was
surprising was at the depth of dormancy vinifera can take almost as cold a temperature
as Concord*.  However as temperatures warmed and fluctuated towards spring, the
vinifera were far quicker to shed their dormancy and slower to return to dormancy.  So
at a certain point they were far less hardy that the Concord because they were no longer
as dormant.   Which makes sense as vinifera are from a mediterranean climate, which is
affected by maritime temperatures and fluctuate less than temperatures on a more
continental east coast.
 
* (the testing was done using exothermic detection (as water freezes it releases
a spike of warmth to settle into its new state (ice).  Grapes put under these tests had
two spikes (one when the water between cells froze) and then another when the water
in the cells froze (bud kill). 
 
Chris Mauchline
SE PA, zone 6
40° 5' N 75° 51'W
~650 ft elevation



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