Koreans hang garlands on doors because garlands represent pure selling and sacredness, and hanging on doors means praying for peace.
Relevant appendices:
1: The garland was introduced into Korea from western countries. As Korea is now the largest Christian country in Asia, this tradition can be continued.
2:? The garland is a traditional holiday ornament in Europe and America, and the material of the garland also has its own meaning. When decorating your home (doors, windows, walls, fireplaces, etc. ) At Christmas, you will greet Christmas with a wreath. Today, garlands have been used as daily home decorations.