Marginally Zone Hardy

April 1, 2018



The main limiting climactic factor for potentially perennial plants in our gardens is whether or not the species is winter hardy (e.g., will it survive to the next year outside in our climate, understanding that our winters can be very mild one year and severe or with damaging variation or extreme another).  This is particularly a concern when it comes to woody plants since their above ground tissue cannot be protected, especially as the specimen gets bigger.  The problem can manifest as not killing the specimen but rather somehow impacting its growth, behavior or appearance (i.e., stunting, dieback, reduced flowers and fruiting or affecting the amount and kind of leaves).  The affected woody specimens generally look bad, even with good pruning. and may takes years to recover.


Japanese Black Pine (Pinus thunbergiensis) is a neat species--it has great needles and the white candles (the new terminal growth) produced in spring are irresistible--but it (all cultivars) does not like central Indiana.  NOTE:  The species will do fine as long as the maximum low temperature stays above -10.  But factually, our central Indiana average low for the past 43-years is -7, and more importantly, it has fallen to more than -10 thirteen times in that period.  The specimen in the photo above did fine the previous 5 winters, but the -13 of 2018 damaged many of the needles.  I have seen enough.  So, it will be extracted come warm weather and its spot given to a more tolerant (hardy) species.  It is not what we want but rather what the plant can tolerate.  Even excellent cultivation and optimal siting cannot supersede reality.  Do not presume that just because a plant is available at a garden center near you that it is hardy, or it may be only when properly situated, and if lucky.



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