This day marks the marriage of Bhagwan with Tulsiji. The daughter of Kushdhvaj, Vrinda was married to the son of the ocean, Jaalandhar. Vrinda was a very beautiful, virtuous wife (pativrata).
The story goes that the demon Jaalandhar was nearly invincible because of his wife Vrinda’s piety and devotion. The only way to defeat him was to break her chastity. Lord Vishnu assumed the form of Jaalandhar and deceived Vrinda. When she discovered the deception, she cursed Lord Vishnu to become a stone (shaligram). She then gave up her life.
Out of compassion for her pure devotion, Lord Vishnu resurrected her as the Tulsi plant (holy basil). He declared that henceforth He would be incomplete without Tulsi, and that she would be His consort. The annual celebration of Tulsi Vivah commemorates this divine union.
Tulsi Vivah also marks the official end of the Hindu wedding season, which had been paused during Chaturmaas. It is observed by performing a formal marriage ceremony between the Tulsi plant and a Shaligram stone (or sometimes a murti of Lord Vishnu/Krishna). Married women observe this ceremony for the longevity and wellbeing of their husbands.