One of the most famous traditional Iranian festivals is Sizdah Bedar, also known as Nature's Day. On the thirteen days of Farvardin (on 2 March), Iranian spend the whole day in nature because they believe this day is a cursed day.
The historical background behind this idea is that more than 70000 Iranians were killed in this special day in Xerxes's period.
The story begins when the king got mad at Vashti, the Queen, due to Mordecai's rumors, so in order to dishonor her, the King commanded her to be presented naked in the court. Vashti refused his command, therefore, she got executed.
King needed a Queen, so there were plenty of women to be introduced to him but there is a Jew girl named Easter who was brought to the court by Mordecai. Haman, prime minister of king Xerxes, made a decision to send some sinner Jews to exile. The night before Haman took any action, Easter made the king dead drunk and he signed an order. The command was not only for killing Haman but also the massacre of a lot of Iranians who were his followers and supporters.
This incident happened on the 13th day of Farvardin. Iranian in this special day run to nature to be protected." Sizdah" means" thirteen" and "Bedar" means "outdoor". So, Iranian prefer not to stay indoors because of the slaughter of many Iranian in their houses.
In this day Iranian get together and have fun. They eat many different goodies from morning till the end of the day. Mostly they have kebab for lunch and pottage for their evening time. Nuts and Lettuce eating with Sekanjabin (a type of syrups, made of vinegar, sugar, and water) are inseparable parts of this festival. Besides eating, playing games are considered as the crucial side of Sizdah Bedar.
One of the interesting parts of this day is that single girls and boys tie grasses because they believe in this way nature hear their prayers and till the next Sizdah Bedar they would be married.
As Iranian are fans of plants, one of the elements of Haft Seen (Seven factors start with a Persian Letter "Seen" سین), they plant grass on a dish which is a custom to throw it to the river on Sizdh Bedar which means at the end everything will return to nature.
There are plenty of festivals held in Iran but some of them are the most crucial ones and Sizdah Bedar is one of them.