Much of what we do for decorations is based on tradition and preference. The General Instruction of the Roman Missal (GIRM) provides direction on how the Mass should be celebrated. It is very specific about aspects of the liturgy that are to be the same everywhere but more general about other areas, leaving it to local bishops to provide guidelines. Church decorating is one of those latter areas.
The GIRM offers this useful bit of wisdom: “Moderation should be observed in the decoration of the altar.” The paragraph specifically addresses floral decorations in Advent (shouldn’t overshadow the joy of Christmas) and Lent (no flowers, with some exceptions). In general it says that flowers should be used sparingly and never on top of the altar itself. But that is the only specific thing this document has to say about seasonal decorations. If you are interested in helping decorate, please contact Nora LaPlant or Ann Walters for Our Lady of Lourdes, or Kathy King for St. Joseph’s, or notify the parish office.