My wife and I went on a garden tour in Winnipeg this past summer and we saw just how popular the practice of growing trees and shrubs in containers has become — many of them grown as standards. Such plants are not inexpensive, particularly when many of the standards had woven stems and were quite a good size. There were cedars of all kinds — one ingenious gardener buys inexpensive potted cedars in the spring, uses them in his summer garden and then uses them as outdoor Christmas trees in containers in the winter garden. Of course they will be dead by springtime but they have served double duty at a bargain price.
We saw combinations of evergreens in containers as well as specialty shrubs such as smoke bush and barberry. Of course exotic tropical trees and shrubs are very popular container plants, such as hibiscus, climbing roses, banana trees, bougainvillea, hydrangeas and oleander. I was interested in hearing how the gardeners wintered these plants.
Banana trees seem so immense and I would have thought impossible to store for the winter. However, one gardener simply chops the tops off the trees, digs the root balls out of the containers (the root ball is actually not that big), and stores them in the basement in cardboard boxes buried in peat moss.
Coniferous evergreen trees and shrubs are relatively easy to overwinter. The plants are simply popped out of their containers and heeled into the ground somewhere in the garden where they will be protected from cold winds and desiccating winter sunshine.
Some gardeners we met went to a lot of effort to overwinter some of the plants. One lady dug trenches and buried her potted hydrangeas and climbing roses. The trench was dug deep enough to accommodate both the container (or the root ball if the plant had been slipped out of its container) and the plant. It was lined with dry leaves and then the tree was placed in the trench, sometimes being covered with dry leaves or a burlap sheet before the trench was filled with soil.º This procedure was used for plants that were rated Zone 5 and above.
One method to overwinter borderline hardy plants successfully is to group them in a sheltered spot, surround them with a wire cage and fill the cage (completely cover the plants) with dry leaves or other mulch. Some sort of covering is necessary to keep the mulch dry so that it does not lose its insulating ability. The more mulch that is packed around the outside of the pot grouping, the better. Some plants, if they naturally go dormant for the winter, can be stored in a garage where the temperatures remain above freezing. Keeping them in the dark will lessen the chance that they will break dormancy too soon in the late winter.
Not everyone has the space — or the desire — to overwinter a tree or standard in the house. For those of us lucky enough to have an all-season sunroom, such plants can be kept alive for the winter and might actually put on a decent display for some of the time. A number of years ago I overwintered a hibiscus standard successfully indoors in front of a south window and it bloomed for most of the winter. I did have to be diligent about insect control as many tropical plants are prone to insect attack when moved indoors, where the air is dry.
When taking plants from the outdoor garden indoors, give them a good spraying with the garden hose and perhaps a preventive spray with insecticidal soap to reduce the threat of insects getting established on the plants.
It’s difficult to see plants succumb to killing frost in the fall if they can be saved and used in the garden again the following year. Try some of these ideas about how you can overwinter your prized plants and maybe you won’t have to buy new ones next spring.