Overwintering Dwarf Alberta Spruce Growing in Containers

I have two dwarf Alberta spruce growing in large plastic pots. How should I keep them over the winter in my Minnesota garden?

Trees, shrubs and perennials growing in containers need extra care for winter. Large containers and plants one or two zones hardier than your area can survive outdoors in the landscape. Dwarf Alberta spruce, hardy in zones 2 to 6, but subject to winter burn whether grown in ground or in planters. I have seen these plants survive the winter in above ground planters in sheltered areas. You may want to provide added insulation to increase winter survival. Bury the pots (if not decorative) in an unused garden area for the winter. Place the Alberta spruce in a sheltered location out of winter wind and sun. Or move the planters to a sheltered location. Insulate the roots by surrounding the containers with bales of straw or hay. Water whenever the soil is thawed and dry.