The 12th day from the day of Deepavali (Uthwana Dwadashi; Dwadashi – 12th day) is believed to be the wedding day of Tulasi and Lord Krishna. Tulasi is considered as a sacred offering to God and there are many stories revolving around the same. The significance of Tulasi is sketched out in one popular tale known as Sri Krishna Tulabhara, in which Krishna was weighed in gold and even the entire jewelry of His consort Satyabhama on the other scale could not outweigh Him, until a Tulasi leaf was placed on it .
There is also a pretty common folklore surrounding the churning of the ocean of milk by the devas and the asuras [Gods and the demons] in search of Amrutha [nectar]. It is believed that along with all the gems and treasures which emerged from the ocean, there emerged Tulasi too. Known to be the sister of Goddess Lakshmi, she was devoted to Lord Vishnu and wanted to marry him. But Lakshmi who was already married to him did not like the idea and cursed her to become a plant. Thus the tulasi plant was born. Thus, offering a Tulasi leaf to the Lord is considered as one of the highest forms of offering.
The Pooja to Tulasi plant is usually performed in the evening. A twig of the Gooseberry tree (Amla) with a few fruits, which represents Sri Krishna, is set by the side of the Tulasi plant. The Brindavan [special pot for the Tulasi plant] is decorated with mango leaves and flowers. Lamps made out of five gooseberries are lit in front of the Brindavan and oil lamps are lit all over the house, and Arati is performed to Tulasi.
When we were kids, Mom and Dad had to hide some crackers from us in secret-places to keep them reserved for this day. Celebrated as Mini Diwali, this festival is hugely popular in our side.
Just thought of sharing this as its nice knowing about customs and traditions in different parts of the country :) Can u ppl throw more light on the festival if u celebrate/ know something more about it?