Answer: You might try dwarf Alberta spruce, however it is very difficult to keep evergreens of any kind alive in containers outside during the winter so I suggest this with some hesitation. They are subject to the stresses of freezing and thawing soil as well as to extreme cold at the roots because they lack the insulation provided by being planted in the ground. The larger the container and the more protection from wind, the better their chances of surviving. Also be sure to use a good quality potting mix formulated for container plants, use containers with drainage holes in the bottom, and water as needed to keep the soil slightly moist any time it is not frozen. However, despite your best efforts, I would not really expect them to make it for the long term. In my experience those that manage to live through the first winter often show signs of stress the following summer and tend to die out in the heat of August. If you really want a reliable look you could consider trying some of the artifical trees, or possibly try spray painting the boxwoods you already have, or use something else decorative such as colorful cut twigs or swags of seasonal greens in the containers. I'm really sorry I can't be more encouraging.
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