Proper maintenance is necessary to protect your concrete art from the freeze-thaw cycles that occur in the winter. Any piece that can hold water, snow, or ice
[this includes planters and statuary and not just birdbaths and fountains] can be damaged.
Here are some tips on how to minimize possible winter damage.
If a planter is left planted over the winter, raise it up off the ground.
If a planter is going to be empty over the winter it is a good idea to store it in the garage, shed, or porch away from the elements.
If a planter cannot be moved into a garage or shed; empty it and turn the planter upside down. Place the planter onto wood strips, cover or wrap with burlap or any absorbent material, and finally cover it with dark plastic. This will prevent moisture from getting into the planter.