Sepandār mazgān is the celebration day of love and earth in ancient Iranian culture. This day is dedicated to
Spenta Armaiti, Spandārmad in middle Persian, the middle Iranian language/ethnolect of Southwestern Iran that during Sassanid times (224-654 CE) became a prestige dialect and so came to be spoken in other regions as well.
It is celebrated the 29Th of Bahman in
Iranian calendar. Modern folklore dates the celebration to ancient times and Zoroastrian tradition.the original date for this ceremony is 5Th of Esfand, and a popular revised date of 29Th Bahman is due to the disorganized calendering during the past 20 years.
(Text is written according to wikipedia)
I am sorry that some Iranian people do not know anything about this event in their culture and celebrate the Valentine day (which is refer to another culture) instead of it.