When I first started gardening up here at 10,000 feet, I asked the local
"experts" if they knew how cold it was under the snow because I wanted to
ensure the survival of purchased plants that came with cold-temperature
limitations. Most people assumed the temperature was the same under the snow
as it was above the snow on any given day. I decided to find out for myself.
I set up an electronic thermometer that had a long, insulated wire attached to
it and a temperature sensor at the far end. I placed the thermometer in a
sheltered, wooden box above the snowline, next to one of my gardens. I dug out
the few inches of snow that had already started to build up on the bed in early
November and placed the temperature sensor on the surface of the soil. Then I
gently replaced the snow. To make sure the thermometer was working properly, I
set up an identical unit outside my glass-covered cold frame and ran the
temperature sensor inside, pinning it to the snowfree soil surface in the
closed cold frame. Every day throughout the entire winter I checked and
recorded the maximum and minimum temperatures in both the raised bed under the
snow and in the cold frame where snow periodically accumulated on and melted
off the glass lid. The results surprised me. Under the snow, the temperature
was constant day and night, staying about 2 degrees below freezing (+30F/-1.1C)
on average. During a period of sub-zero weather when our low temperature
dipped to -15F (-26.1C), the temperature under the snow dropped to +26F
(-3.3C). That drop, however, was delayed by 2 days. When the ambient
temperature then warmed to around +15F (-9.4C), the temperature under the snow
stayed at +26F (-3.3C) for 2 more days -- another delay in responding to the
change in ambient temperature. At that time, the snow cover was about 18"
(45cm). By comparison, the maximum/minimum temperatures in the cold frame
fluctuated wildly, depending on whether there was snow cover on the glass lid
or not. If the sun or wind cleared the lid of snow during the day, the maximum
temperature would soar above 80F (+26.7C). But then at night the uninsulated
lid allowed the interior temperature to plummet to the ambient temperature --
as low as -15F (-26.1C). A layer of snow just 4" (10cm) deep on the raised bed
was enough insulation to protect the soil from freezing. It's possible that
the temperature 6" below the soil surface at the root zone may have stayed
above +32F (0C) throughout the snow-covered period. By the time the snow
cover had thinned to the point where it no longer provided significant
insulation, it was late spring and the minimum ambient temperatures were
between +20F and +34F (-6.7C and +1.1C). Coupled with longer, warmer daylight
hours and sunnier skies, the soil was not affected by the below-freezing
nighttime temperatures due to its greater density than the surrounding air,
which means it took longer for the stored heat from the day to be radiated into
the cold night air, and the added protection of the surrounding rocks which
acted as a heat sink. The fluctuating temperatures in the cold frame taught me
that I would have to use great diligence to keep a heavy layer of snow on the
glass lid or risk losing my overwintering plants. This became an impossible
chore, especially when we left for several weeks in the dead of winter to warm
our bones in the Mojave Desert. So I gave away my cold frame and instead built
Garden #11 in its place. There is a very interesting book that deals with the
temperatures and climate near the ground. I found an except of it many years
ago and it helped me in my quest to understand the climate under my snow cover.
In its translation from German, it's called "The Climate Near the Ground" by
Rudolf Geiger. Originally written in 1927, it has been translated and updated
several times. It can be read on line or download for free at
http://www.archive.org/details/climatenearthegr032657mbp. Jane HendrixMountain
View Experimental GardensPeak 7 Area - Breckenridge, Colorado U.S.A.Elevation:
10,000 feetUSDA Zone 4Website: http://www.picturetrail.com/hendrix
---------- Original Message ----------
From: cohan fulford <[email protected]>
To: "Alpine-L, the Electronic Rock Garden Society, postings copyright by
authors." <[email protected]>
Subject: Re: [Alpine-l] Springtime photos
Date: Fri, 15 Apr 2011 22:56:17 -0600
I read somewhere about a climate zone rating system in Russia which made use of
many more factors than minimum lows.. would be interesting to have something
like that, but of course, more factors that could be wrong :))
I actually have no idea how cold it is/gets under our snow pack, which is much
less and of shorter duration than yours, though considerably more and longer
lasting �than in places like Calgary (where, it should be noted, many
things rated for much warmer zones survive in years with little snow cover at
all.. of course often little is actually known about the hardiness of various
species outside regions with the most gardeners), and varies considerably from
one part of my property to another, within a few metres one way or another in
some cases! Certainly nothing is growing under the snow here, with the soil
solidly frozen before snow cover, generally, and for some time at least
�after melt as well!More forecast for tomorrow--looks like a late spring
here this year!Cohan
On Fri, Apr 15, 2011 at 5:18 PM, [email protected] <[email protected]>
wrote:
Indeed, Cohan,�there was even more snow depth than is pictured in my
photos taken April 12 so there has been some snow melt already.�
However, the overall indicator of snow melt progress is the volume of water in
the Blue River which flows from the west side of the Continental Divide through
Breckenridge, down to Lake Dillon (Denver's water supply) and into the Colorado
River Basin.� As of today, the water level�in the Blue River is
still low.� The local newspaper has been warning residents that our
river could flood this spring due to the increased snowpack.� May and
June are usually our heaviest snow melt months.� Even in early July it
could be problematic trying to cross on foot some of our back country streams
where there are no bridges.� By late July, the river and creeks have
"calmed down" and are at a normal summer flow.��I don't put much
stock in an area's USDA zone designation.� Those zones are based on the
coldest ambient temperature recorded for a given area.� My Zone 4 says
it can get to -30F (-34.5C) but it never has been that low in the 18 years
we've lived up here or in the 48 years Klaus has been coming to Breckenridge to
work and ski.� Also, the zone designation doesn't consider an area's
winter snowpack.� At our house, the snowpack begins around the first
week of November and is still providing an insulating blanket for the soil
through mid-May.� The temperature at the contact point between soil and
snow stays around 32F (0C), fluctuating only 2 to 3 degrees downward when we
have a period of sub-zero F. ambient temperatures.� Our snow is never
icy and is full of air, even when it's compressed.� The plants are
protected from biting winds and extremely cold temperatures and actually
continue to grow under the snow, forming new foliage and even flower
buds.� They are also protected from March and April days of unseasonably
warm sun that might induce them to break dormancy prematurely.� Because
of my reliable snow cover, I have been able to grow species listed as hardy
only to Zone 5 and even 6.���Just 20 miles from here, on
the east side of the Continental Divide, the winter climate for plants is far
more severe.� That area, around the little towns of Alma, Fairplay and
Hartsel, is designated as Zone 3, even though they are at or below the
elevation of our gardens.� Being in the "rain shadow" of the Rocky
Mountains, they get very little snow throughout the winter months.� To
make matters worse, fierce winds sweep across the naturally-open, park-like
meadows, removing what little snow may have fallen on the plants.� With
mostly clear winter days, the sun beats down strongly through the thin
atmosphere, warming and heaving the frozen soil, ripping apart the root
systems. �Every spring, gardeners lose several perennials to that harsh
winter climate.��One winter I tried to keep the path to the
compost pile shoveled but it was a losing battle.� We have a half-acre
lot and the compost pile is at the back end, about 250 feet or so from our
house.� I would get the whole thing nicely cleared and then the winds
would come up during the night and fill in the path with windslab snow.�
After repeating that operation several times with the same result and throwing
out my back in the process, I finally gave in to Old Man Winter and strapped on
snowshoes to get to the back of our lot.� We had so much snow this
winter that I couldn't even keep my broken snowshoe path open!� Again,
it was Mr. Wind who filled in my neatly packed track with 12 inches of
new�snow during the night while I was in dreamland.��Jane
HendrixMountain View Experimental GardensPeak 7 Area�- Breckenridge,
Colorado U.S.A.Elevation: 10,000 feetUSDA Zone 4Website:�
http://www.picturetrail.com/hendrix ����West
Central Alberta, Canada, Zone 2-3
record temps from 10-20 miles away:� min -45C/-49F;max 34C/93F�
http://picasaweb.google.com/cactuscactus
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