Ksheerabdhi Shayana Vratham (Ksheerabdhi Dwadashi) is observed on Shukla paksha Dwadashi in Karthik Month. In 2013, Ksheerabdhi Shayana Vratham date is November 14.
According to several Puranas, Lord Vishnu, who woke up from cosmic sleep on Utthana Ekadashi, comes to Vrindavan or Brundavan along with Goddess Lakshmi and Lord Brahma.
It is also believed that on this day, Ksheer Sagar Manthan (Churning of the Milk Ocean) for Amrit (nector) was started by demons and Gods.
Hence, worshipping Tulasi plant along with Sri Maha Vishnu on this day gives many meritorious results.
Deeparadhana on Vishnu temples are most preferable ritual to perform on Ksheerabdi Dwadashi. Those who protect the diya lighten by others will also get good benefits. Tulsi Damodar Vivah is done today in most of the places.
Ksheerabdi Shayana vratam is a main ritual during Karthika masam in Karnataka and Andhra Pradesh.