The Q&A Archives: Overwintering Container Plants

Question: I live in Toronto and have a garden on my roof. I have had poor results with perennials in pots overwintering outside. However, I now have an azalea, a hydrangea and a climbing hydrangea, all of which I really want to preserve over the winter this year. Any suggestions?

Answer: The tops of the plants you mention should winter over without problem, but the roots will need some protection. Since the roots are the least hardy parts of a plant (they rely on soil depth to protect them from temperature extremes), you'll need to insulate the roots to keep the plants alive. You can strap 1" styrofoam sheets around and beneath each pot and stuff newspapers in the openings between the insulation and the pots. Or, you can make a cold-frame of sorts using clear plastic and styrofoam sheets for the floor and a for few feet of sidewalls, draping the plastic over a frame above the plants. The plastic will have to be carefully monitored, however, because it will absorb and radiate heat during sunny weather, even if the air temperatures are freezing.

With a little extra protection your containerized garden should survive the winter months.

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