The end of Chatur Masya is signified by Devottana Ekadashi when Lord Mahavishnu wakes up after a 4-month period of yoga nidra. The next day, i.e. Utthana Dwadashi, commemorates Tulsi Vivaha when ages ago Lord Krishna wedded Tulsi.
On Devottana Ekadashi, Tulsi plant is readied with an amla berry or Indian gooseberry and Vishnu Pada placed in front of the plant. Beginning that day, deepadana or lighting of oil or ghee lamps has been specified to beget benefits. Early morning, on Dwadashi, Mahavishnu, who is lying on Sheshashayana, is woken up with suprabhatam and other ceremonies.
Tulsi plant’s Vivaha is performed with an amla plant or sugarcane, representing Lord Krishna. During the ceremonies, saligrama and amla berry are kept on the soil of the Tulsi plant. Artistic people decorate Tulsi plant and Lord Krishna as the bride and the bridegroom.
A yellow thread is wrapped around the Tulsi plant and the amla plant/sugarcane, 7 times, representing the 7 pheras. Garlands are exchanged between Tulsi and amla plant/sugarcane. A mangalsutra is placed around Tulsi plant.
Some families perform the ceremonies with kumbhas representing Tulsi and Lord Krishna. Others perform the ceremonies with kumbhas as well as between the plants on the terrace or balcony.
Aarti with minimum 5 amlas having battis dipped in ghee is performed. The ceremonies go on till Poornima for 5 days. On the final day, udhyapana is performed.
Kartigai month continues till Amavasya. On these days, lighting oil lamps is significant. In North India, people do not light any oil lamp in front of Tulsi on Sundays. We have no idea, why.