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  • From: "Dean Kreutzer" <deankreutzer@hotmail.com>
  • To: nafex@lists.ibiblio.org
  • Subject: [NAFEX] Blackberry Hardiness Question
  • Date: Tue, 19 Oct 2004 09:37:53 -0600

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 temps.

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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