Pushing the Limits

We all know someone who likes to push the limits.  They like to see how far they can go without consequences.  However, I am not talking about people in this article.  I am talking about pushing zonal limits.  Did you know that in some cases, plants have not been tried beyond the zone listed on their tag?  Environment Canada began a study a few years back wherein they asked for volunteers throughout the country to try plants of their choice that were rated beyond their zone.  They were to record how the plant fared.  One goal in this was to determine if the zone map for Canada needed to be changed due to climatic changes.

I did not formally take part in this study but I have tried a few plants within my own garden rated a zone 4 and found them successful.  For example, barberry.  I have 3 Rose Glow Barberries (berberis), one Golden Nugget Barberry and another whose tag has long since disappeared but it is a dwarf yellow variety.  All those planted within my back yard do great with very little dieback.  The two Rose Glow Barberries in the front are a bit more exposed to the elements and had more dieback this past winter than the previous three years.  They are recovering quite nicely though.

Endless Summer Hydrangea is a zone 4.  It dies back to the ground for me every year despite mulching and burlapping.  Each year I hope for a long summer so it will have a chance to bloom.  Thank goodness it blooms on new wood as well as old.

Black Lace Elder (sambucus nigra) is another zone 4 in my garden.   It is in a very sheltered location close to the house but it dies back each year.  A quick grower, it regains its height and more in any given year.  Incidentally, this elder has never flowered for me.  Perhaps this is the year.

A neighbour grows a Crimson King Maple (acer platanoides Crimson) in his front yard.  It is fully exposed to all elements and does die back a bit after a bad winter but comes back in full glory.  It is a beautiful variation of maple with large crimson leaves which intensify in the fall.  A Norway Maple, it is absolutely stunning!!


I tried a Japanese Maple overwintered in the garden one year.  It is a zone 5 but no amount of mulch and burlap could save it its first winter.  Don't bother trying to overwinter it in your house.  Powdery mildew is a major obstacle here. 

I had customers who grew Cherry trees with great success.  I am not talking Evans Cherry or North Star (zone 2) which are both hardy here.  I mean a tree similar to the Bing Cherry with sweet fruit.  A lot of labour went into protecting one particular gentleman's tree.  He built a wooden raised bed.  Planted the cherry deep.  And in the fall he cut styrofoam sheets to fit in the bed around the trunk to insulate the roots.  I think he may have even mulched on top of that!  He swears it works!  Part of the key to success here too is watering well into the fall to create a proverbial block of ice around the roots.  This helps irrigate as the ground thaws and assists in protecting the plant from the upheaval of the soil during the freeze and thaw sessions every spring.

Many perennials can be grown successfully in a "lower" zone.  Here you have the advantage of the ease with which you can mulch a bed of perennials.  Water well into the fall too.  I have grown heucheras successfully for years in zone 3 that were rated zone 4.  This last winter I lost a few but have a few seedlings that self-sowed to replace them.  Try Palace Purple Heuchera (coral bell).  



Another is Astilbe.  I've grown Bridal Veil, a white one, rated zone 4, in the shade for at least eight years with success.

You might try the evergrowing variety of Echinacea such as Double Decker, Razzmataz, Harvest Moon or White Swan (all zone 4).  They don't like a heavy clay soil or wet feet.  Supply a well-drained soil and they will respond accordingly.  Especially important, be sure they are not planted where puddles form in the spring as snow melts.  Be courageous, and give a new plant a try.  You just never know.

Have you success stories in pushing zonal boundaries?  Let me know in "comments" please.  I'd love to hear about it!!