Growing Things: Getting the hang of borderline hardy plants

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Q: I have a question to which I have not been able to find an answer.  On impulse, I purchased a lovely Pieris japonica — “Mountain Fire”.  When I bought it, there was no information with it other than the name and “Keep moist” on a label on the container.  We planted it a couple of weeks ago in a place where it receives morning light and afternoon shade.  To my dismay, in trying to find information about the plant and how it might survive an Alberta winter, I learned that it is only hardy to Zone 4.  Do you have any advice on how we can protect this very pretty plant over the winter?  It seems quite happy right now, but I worry about it when the temperature hits -40C.

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A: One of my hobbies, as a gardener in the Edmonton area, is to push the envelope when it comes to trying to grow plants that are rated as not being hardy here. I have tried many, many plants over the years some with more success than others but all interesting experiments nonetheless.

The problem with the Pieris is that it is an evergreen plant and I have found that borderline hardy plants that are evergreen have a harder time surviving our winters than those that are deciduous. The best place to grow the Pieris would be a semi-shaded spot that is protected from the winter winds by a fence or building. I would erect a burlap screen in front of the plant in the fall. The screen will help to keep off the winds and sun that can also damage the plant in winter.

Do not wrap the plant. I would also pile snow around the base of the plant in an effort to insulate the roots as much as possible.

The alternative is to repot the plant in a container. Once the cold winds of fall arrive you could bring the container into your garage. Wrap the container and plant in home insulation and check it regularly to see if it needs some water. I know this sounds like a lot of effort but if successful it is well worth the effort.
This question did remind me of a fellow I interviewed once for a column. His passion were Japanese maples which of course are not hardy for our climes. He actually converted one of the bedrooms in his home into a winter sanctuary for 6 of his Japanese maples in containers and would carry them in every fall and back out again in the spring. My dedication to trying borderline hardy plants never reached that level of passion.

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Learn more by emailing your questions to [email protected], reading past columns or my book Just Ask Jerry. You can also follow me on Twitter @justaskjerry01.

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