Evergreens planted in containers must be winterized in areas where the temperatures and winter conditions are harsh, as the root structures are not insulated by layers of ground soil. Choose to grow potted evergreen plants that are winter hardy in your USDA growing zone or lower, as this will increase the winter survival rate. Plant the evergreens in containers large enough that additional soil surrounds the roots for insulation. Choose containers that are not fragile and will winter well in freezing conditions. Wood containers tend to hold up better than decorative pottery.
Find a garden location where there is space to use the ground for natural insulation by digging a hole and burying the pots. Choose a location that is protected from wind if possible.
Apply heavy mulch over the buried pots for additional insulation and reduce the chance of root heaving and damage.
Move potted evergreen containers close together in a protected location if they cannot be buried. Wrap the sides of the container with two to three layers of bubble wrap to protect the roots and containers.
Cover wrapped containers with heavy mulch that surrounds and covers the pots.
Create a wind block in areas where there is no natural wind protection. Pound several metal stakes into the ground to surround the trees. Attach burlap sheeting to the stakes to create a fenced screen around the trees.
Remove the burlap screen and mulch covering from the plants and pots in early spring once the ground begins to thaw.
Dig up the pots once the ground is thawed to a point where the shovel penetrates the soil.