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Re: Re: REF: zone maps

Linda Mann <lmann@volfirst.net> wrote:
Thanks all for the zone maps, but those are usually too general for a
specific location/microclimate.

I'm trying to find out what zone the hybridizer's garden is in, which
sometimes isn't what the map shows.

I sign my posts zone 7/8 - jokingly. Not sure what zone this place
should really be considered since the winter low has been down as far as
minus 25 F (zone 4), used to always go down below zero at least once
each winter, which would be zone 6, but hasn't been below 10oF for the
last three winters. 10oF puts me in high zone 7, approaching zone 8, &
I figure a few more years of global warming will probably put me solidly
in zone 8a.


You have raised some interesting points here. There certainly seem to be definite, and over the short term at least, irreversible climate changes that are occurring. For example, I am located in Zone 4b, which is defined as an average annual minimum low temperature of -22F. We have not experienced temperatures at that level in more than two of the last ten years, and in most of the rest of them the lowest temperature has not approached within 15 degrees of that level.

I am wondering, however, if the data are really available to sustain the endeavor you have launched upon. How do you validate statements about individual hybridizer's microclimates? Given ongoing climate changes, how do you account for this over time in a specific location. The most accurate Zone designation for a garden in which a cultivar was hybridized and grown 25 years ago might considerably differ from conditions in the same garden today. How much reliance can you place on the information you are receiving from different sources on the Zone designations of specific gardens?  It is generally regarded as a fallacy to draw conclusions that are more precise than the data on which they are based.

A totally different issue is the question of how indicative USDA Zone designations of the average annual lowest temperature are of reblooming iris performance. After all, this refers to a particular datum that relates to a season when no irises are blooming except in the mildest climate areas. I would think that perhaps the average length of the frost-free growing season would be more predictive of reblooming iris performance than the absolute low temperature that is reached in the depths of winter, though obviously these two items are not uncorrelated (but I expect that correlation is much less than perfect).


Jeff Walters
in northern Utah
(USDA Zone 4)

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