Re: Hardiness of Species Irises

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Winter (cold) Hardiness: 

 

How timely, I was just sending messages about cold hardiness this morning to a local group (that is redoing the Woody Landscape Plant materials Manual of Alaska.)

I totally agree with Sean Z. about need to quantify cold hardiness factors or combination of factors.    (Sean said: If so, I suppose there need to be some standards across the data, such as no snow cover in a fully-exposed location. On the other hand, a list of locations where species have been grown outdoors successfully might be more useful since you can then take into account climate conditions other than temperature when deciding to try a species. It might be something to try to integrate into the species database.)

Sometimes when people say that a plant survived a certain temperature it was only for one night or only a few hours that one night.  In addition, we do not know if there was a snow cover or not, or how deep the snow was.  If the snow was deep then the plant probably never even got close to that low temperature, and in another scenario there could be no or little snow and the wind is blowing – a MUCH tougher condition than the deep snow situation.   (Before global warming we used to have a reliable snow cover.  It came early and lasted all winter.  We grew many more plants before - because now we usually have at least one prolonged warm period that melts our cozy cover of snow.  The very cold tolerant plants start to grow during the “Chinook” (before winter is really over) and thus dye when the cold returns.  The less cold tolerant plants are also not making it anymore because they do not have the moderating effect of the snow to mulch them from the cold that comes later.

The USDA hardiness zone map is COMPLETELY WRONG for Alaska.  I am always disappointed that is does not get corrected on updated editions.  It looks like some extrapolated the theory that coastlines are warmer than interior areas without any actual data to back up the preposterous zone designations given to Alaska.  (Not to mention the permafrost, short growing season, and cloudy/rainy factors.)

 

Debbie Hinchey

Anchorage, AK

Now, finally, under a foot of snow.