[gardeners] Zones -- long

Liz Albrook (gardeners@globalgarden.com)
Fri, 10 Apr 1998 14:09:57 +0000

Margaret Lauterbach <gardeners@globalgarden.com> wrote:

> At 01:21 PM 4/10/98 -0700, you wrote:
> >On Fri, 10 Apr 1998, Margaret Lauterbach wrote:
> >Six, according to my big  USDA wall map.  What's the average minimum
> >winter temp?  That gives you the zone.
> >
> >Kay Lancaster    kay@fern.com
> >
> I know, Kay, but look how many degrees north Lewiston is from Boise,
> and no maritime influence.  Must be warm currents coming up the
> Columbia/Snake that moderate the temp.  Margaret

It might come as a big surprise but I know how the USDA comes up with 
their zone designations.  We do have strong maritime influence, 
though not a maritime climate, from the winds coming up the Columbia 
Gorge.  As I'm sure you guys know, that's why Walla Walla and the 
Tri-cities areas in Washington have such incredibly long growing 
seasons and such mild winters.

At the junction of the Clearwater and the Snake Rivers where I live 
there are only two significant elevations to the north.  There's the 
river bed elevation that's always zone 7 and there's the Palouse 
elevation, some 2300 feet higher that is zone 5/6.  To the south, my 
side of the river, there are 3 elevations -- the river bed, Lewiston 
Orchards where I live that is some 1000 feet above the river and the 
Camas Praire some 1200 or so feet higher than the Orchards.  The 
Camas Prairie is zone 5/6 and in some places 4.

The reason that the old USDA map has zone 7 and the new one has zone
6 is that official temperatures used to be recorded down at the river
bed level and are now recorded at the highest elevation.  I live
between those two points.  To illustrate the variations in climate
in this area,  the river level early spring flowers blooma week or so
before they bloom at our house and they bloom about 3 weeks or more
later on the Camas Prairie.  Our growing season is 20 days shorter
than the growing season at river level but 55 days longer than that
at the Camas Prairie or Palouse levels.  The important part about the 
elevations is that we recieve some protection from winter colds 
because we are, to an extent, in a river canyon.

As far as Sunset zones go we probably do qualify as a 3.  Sunset 
tends to be more accurate in terms of winter kill, in my experience, 
than the USDA.  We have a fairly high degree of winter kill, higher 
than one would expect from our temperatures, because of the winter 
winds blowing down the Snake River Canyon.  By the time those winds 
reach us from the mouth of the Columbia, they have gotten quite dry.  
Anything exposed to the wind is apt to die from dehydration.

So now you know why I am never really sure how to explain what zone 
I'm in.  It's not that I don't know or understand, it's just that the 
zone designations don't actually mean much in desert areas with 
rapidly changing elevations.  I haven't lived in this house long 
enough to have enough data to determine what zone my yard is in. 
Margaret, now you know why we are so different from Boise -- for a 
long time I wondered why it was so cold in Boise compared to here.