On the last day of the New Year celebrations, the 13th day of the first month, it is the universal custom in Iran to spend the day outdoors. All people will leave their homes to go to the parks for a very festive picnic.
This day was not celebrated in this manner before Islam and might be the result of several rituals combined into one. This day was devoted to the deity Tishtrya (Tir), the protector of rain. In the Zoroastrian calendar each day is named after a deity and this particular day in the month of Farvardin is named after Tishtrya. In the past there were outdoor festivities to pray to this deity in hope of rain that was essential for agriculture. The act of throwing away the Sabzeh from Haft Sin into rivers and running waters on this day also indicates veneration for a water deity. The act symbolically represents an offering made to such a deity.
However, Anahita was the goddess protector of running water and not Tishtrya. It appears that at least part of the celebration is to pay respect to some water deity. Tishtrya/rain or Anahita/water are likely combined together to preserve veneration for water deities in general. In ancient mythology the deity Vata (the rain-bringer) was associated with Harahvati Aredvi Sura, which means possessing waters (Anahita is a later assimilation of this deity). Aredvi Sura personified a mythical river out of which all rivers flow. Clouds also took up rain from the same mythical river. Every year Tishtrya goes to the river in shape of a white stallion to fight the Demon of Dearth appearing in shape of a black stallion. After his victory, Trishtrya rushes into the sea and water is dispersed all over and Vata snatches some up for the clouds. The rest of the water is mixed with seeds of plants, which sprout as the rain falls. Ancient Iranian rituals quite often enacted their mythologies, waters were respected and many rites existed with respect to waters. It is very likely that several of these were combined to preserve some aspect of the ancient celebrations venerating waters. Up until the 19th Century there was horse races occurring on this day, which very likely represented the fight between the two stallions.
Today Iranians regard this day as a bad omen and believe that by going into the fields and parks they avoid the misfortunes that could befall them. This notion is contrary to the Zoroastrian doctrine where all days were regarded as sacred and were named after venerated deities. The belief that the number 13 is a sign of bad omen is borrowed from the Christians and has found its way into the popular Islamic ideas. According to popular Muslim belief, the 13th day of the month is a day with unfortunate consequences (nahs in Islamic terminology), so it can be assumed that Iranians have combined the two. By going outdoors into the fields, the ancient festivities were observed while the Islamic ideas were also incorporated into the occasion. Muslims today still have a prayer for rain called 'namaz e baran', which is used at times of prolonged drought. In the year 2000 AD, huge communal prayers were organized in Iran with the said prayers during the water crisis in Iran.
All kinds of food and delicacies are prepared with tea, local drinks, fruits, bread, cheese and fresh herbs, noodle soup called 'ash e reshteh' and herbed rice with lamb (baghale polo and bareh) are favourites. Wealthy Iranians will spend the day in their country homes and estates, while the entire day will be spent in their gardens. The occasion is a communal one and close relatives and friends will participate. Wheat or barley shoots (Sabzeh) that are grown especially for New Years and are kept throughout the festivities are discarded in nature mainly in running waters and small rivers at the end of the day. The picnic normally ends with the setting of the sun.
The occasion has no religious significance and is celebrated by all. With the more modern Iranians there is music and dancing while most people will play games and sports. It is also believed that unwed girls can wish for a husband by going into the fields and tying a knot with green shoots, symbolizing a marriage knot. The day should be spent joyfully with no quarrels or bad feelings and all things unpleasant are avoided to make sure nothing bad will happen.