Answer: Unfortunately, it is difficult to grow container plants outdoors year round in your cold winter climate. The reason is that the roots are not insulated as well as they would be in the ground so they are subject to the stresses of oscillating temperatures as well as excessive cold. Evergreens are also prone to drying out in the winter due to either wind or sun reflecting off the building. So while you could try it and see how it works out, please understand you may have to replace your topiaries every spring. The spruces would need a half day of direct sun, preferably morning sun as the afternoon sun would tend to bake them. This would also be true for yews, hollies, or boxwoods which are other possible plants to try. Your local professional nursery staff may have other suggestions based on a more detailed understanding of the growing conditions on your porch as well as your design goals. Sometimes it works well to use a decorative urn that can stand alone as an ornament during the winter, then plant it with seasonal flowers during the warmer months. Or, you could use cut evergreen branches or branches with ornamental bark (such as white birch or red twigged dogwood) during the colder months. Good luck with your porch decoration!
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