[NAFEX] Blackberry Hardiness Question

Dean Kreutzer deankreutzer at hotmail.com
Tue Oct 19 11:37:53 EDT 2004

Hello all,

Hardiness really is a very complicated concept, more complicated than just 
minimum temperature.  I think we all have had experience with plants that 
are supposedly not hardy for our area surviving, and the opposite with 
supposedly hardy plants for our area dying after their first winter.  What 
is more confusing is the fact that 5 out of 10 of these plants live and the 
others die.  Open winters with no snow cover, previous year overcropping of 
fruit, unhealthy or stressed plants, etc. are just a few other factors off 
the top of my head that can have an effect on a plants ability to withstand 
the winter.  It is why I never say "This plant is hardy to -40F", instead I 
say "This plant has survived -40F"

A process called supercooling prevents the formation of ice particles 
forming within the plant tissues itself and each plant has this ability to a 
greater or lesser extent.  Supercooling does not work if the temperature 
goes below -40F however, which is why in the northern Canadian prairies you 
can actually see a division of where certain plants flourish and are 
non-existant based on only the winter temperature lows.

The difference between -10F and -30F is important.  Tests at the U of 
Minnesota in a freezing chamber with grapes have shown that wild grape 
(vitis riparia) and some other riparia hybrids have this supercooling 
ability to around -40F, but at lower temps, ice formulation still occurs and 
the tissue dies.  Other labrusca and vinifera grape hybrids burst at lower 

This is why I believe a few years of testing for hardiness (at least in the 
north) should be done at different sites before any breeder releases a plant 
to consumers.

Sorry for the rant....

Dean Kreutzer
Regina, Saskatchewan Canada
USDA zone 3

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