"Inians have a tradition of spending the day outdoors on the 13th of Farvardin. From very ancient times, people have enjoyed this day, although it is also the day that marks the end of the Norouz celebrations.
The first 12 days of the year are very important, because they symbolize order in the world and in the lives of people. The 13th day marks the beginning of the return to ordinary daily life.
It is customary on this day, for families to pack a picnic and go to a park or the countryside. It is believed that joy and laughter clean the mind from all evil thoughts, and a picnic is usually a festive, happy event.
Sizdah-Bedar is also believed to be a special day to ask for rain. In ancient Iran, every day had its own name, and belonged to a different angel. The 13th of Farvardin belonged to the angel of rain. This angel is depicted as a horse.
Sizdah-Bedar is also a day for competitive games. Games involving horses were often chosen as a victory of a horse represented , the angle of rain.
Another tradition on the 13th, is the knotting of blades of grass by unmarried girls in the hope of finding a husband. The knotting of the grass represents the bondage of a man and a woman. These days, girls sing this song while knotting: " Sizdah-Bedar sal-e deegar khooneh shoohar, bacheh baghal", meaning: "Next Sizdah-Bedar, in my husband's home, holding a baby"!
(courtesy of ketabfarsi)