How do I winterize a planter?

Dirt in the planter should be removed (easily done if some type of liner was used).  The planter should be turned over and checked to see that the drain hole is cleared.  If the planter is too heavy to turn over, proper drainage is a must and can be achieved by simply elevating the planter from the ground by inserting some type of spacer under the base (old pieces of tile, stone or wood). This creates a hollow area under the planter which enables the water and ice to drain away.  Covering the planter with a lid such as wood will prevent excessive ice build up.