There are people who are allergic to flowers.  In this case artificial lei is appropriate.  The purpose of the lei is not entirely just the pua but the spirit of aloha that goes with it.  When you throw the lei in the trash you throw the aloha that the lei was given in the trash as well.  I hang all my old lei in the trees or shrubs in my yard.  Eventually they return to the earth.  The early Polynesians descibed the islands as having lei around them (clouds) when they sailed to these islands.  Nearly every morning I see a lei encircling Maunakea.  The greatest lei is "Kamalei", when a child has its arms around the neck of their parent or kupuna.  Pualei making is a cultural treasure.