Shami Puja is held on the 10th day of the Shukla Paksha of Ashwin month. Shami puja 2012 date is October 24. The rituals and pujas on the day are dedicated to the Shami Tree. Ganesha Purana suggests that worshipping Shami Tree, on the dasami day which is also the Dasara day, will help in redemption of sins.
Shami Tree is widely used in beauty products and in ayurvedic and indigenous medicines. The tree is also held sacred by many communities in
Special pujas are performed on the Dasara day on the base of the tree.
You can read more about the story of Shami Puja and about the tree here in this earlier article on Shami Puja.