Tulsi Vivah is the ceremonial marriage of the Tulsai plant (holy basil) to the Hindu  god Vishnu or his Avtar Krishna. This ceremony can be performed any time between Praboshini Ekadashi – the eleventh lunar day of the bright fortnight of the month Kartik to the full moon of the month Kartik Poornima but usually it is performed on the eleventh or the twelfth lunar day. The day varies from region to region. The Tulsi wedding signifies the end of the monsoon and the beginning of the Hindu wedding season. To participate in Puja – TULASI

Karthika Masam Schedule

Source:Wikipedia