wreath an arrangement of flowers, leaves, or stems fastened in a ring and used for decoration or for laying on a grave.
garland a wreath of flowers and leaves, worn on the head or hung as a decoration.
laurel the foliage of the bay tree woven into a wreath or crown and worn on the head as an emblem of victory or mark of honor in classical times.
The definitions sound very similar to me. When is it appropriate to use each word (and when is it not)?