North American Fruit Explorers mailing list at ibiblio

[Bernie Nikolai <Nikolai@v-wave.com>]

        While I realize many growers in milder climates (zones 6 and warmer)
can successfully prune apple trees now, and anytime in mid winter, I thought
I'd share my experiences in zone 3/2.  In a nutshell it is SUICIDAL to prune
apple trees in my climate in the winter or even the late winter/early spring
months.  A case in point, a neighbour had a large and healthy Rescue Crab of
about 20 years in age.  The local landscape company that did her lawn
convinced her they were "expert tree pruners" as well, and pruned the Rescue
Crab in late February.  Rescue is normally exceedingly hardy and can take
-50F without much if any damage.  The tree was SEVERELY winter injured, and
large sections of the scaffolding branches had to be removed in the early
summer, as they were dead!
        In my own orchard, the best way to winterkill a marginally hardy
tree is to prune it before green tip.  Last year I was nursing several
marginally hardy apples on Ottawa 3 rootstock.  I pruned on April 7, about 3
weeks before green tip in my climate.  Every marginally hardy tree I pruned
died of winterkill and did not leaf out.  Every tree I did not prune of the
same varieties leafed out normally!  That's enough to convince me.
        I think this happens due to dessication (drying out) of the trunk of
(especially marginally hardy) trees through the pruning cuts.  The sap is
just not running, at least in any quantity, and the tree dries out and dies.
I find if I wait until green tip, I'm safe, and the trees seem fine, no
matter how much pruning I do.  So now the only pruning I ever do before
green tip (around May 1 here) is cutting a few sticks of scionwood.  If I
wax the ends of the cuts the tender trees seem to be fine after scionwood is
removed.  I suppose I could wax all pruning cuts, and prune in March or
early April without damage, but that's a ton of work.  So if you live in
zone 3 or colder, definately wait until green tip to prune to be safe.  I
can't speak for zones 4 and 5, but my gut feeling is wait to green tip as
well in those climates before doing any pruning.
Bernie Nikolai
Edmonton, Alberta


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