Telugu, Kannada, Gujarati and Marathi calendars observe this month as Karthika maasam. It is named after Kruthika star which falls on full moon day (pournami) of this month. This month is considered holy month of the year as it is dedicated to both Lord Shiva and Lord Vishnu. Performing Shivalinga puja, and lighting lamps near holy tulasi plant while the stars are visible in the sky is auspicious. Fasting is common on important days, especially on Nagula Chavithi (October 30), Ekadasi (November 6), full moon day (November 10) and all the Mondays of the month (October 31, November 7, 14, 21). Karthika Puranam (sacred scripture about the importance of the month) is read throughout the month. Taking bath in holy rivers like Ganga, Godavari, Krishna etc. is considered a pious act.
Nagula Chavithi (October 30) is observed on the fourth day after amavasya in Karthika maasam dedicated to Nagas or Snakes. Some regions perform this festival on the fifth day of Sravana maasam. The worship of snakes is part of nature worship and it is meant to give the message that each aspect of nature is crucial for the survival of the other. Imbalance in nature will lead to total destruction of all living beings. Snake God is offered milk, fruits, special naivedyam chalimidi (rice flour and jaggery) and chimmili (made of sesame and jaggery) near snake pit or in the home it self, devotees eat only the special naivedyam, fruits and fast for the day.
Uthana Ekadasi (November 6) - Chaturmasa begins on the Ekadasi day after the amavasya in the month of Ashada and ends on the Ekadasi in the first fortnight in the month of Karthika. Lord Vishnu remains in deep slumber during the period. He wakes up on the Karthika Shukla (first fortnight after amavasya) Ekadasi and this day is observed as Dev Uthana Ekadasi. The importance of Uthana Ekadasi is narrated to Sage Narada by Brahma. The divine conversation is found in the Skanda Purana. Observing this Ekadasi is believed to help in getting rid of the guilt associated with sins committed and is also a path to liberation. As any of the ekadasi and specially this ekadasi falls in Karthika maasa, devotees of Vishnu observe fast on this day.
Ksheerabdi Dwadasi (November 7) - Tulasi Vivah is an age-old tradition and is mentioned in the Padma Purana and other ancient scriptures. Tulsi, or the Holy Basil, is the sacred plant of the Hindus and symbolizes purity and is famous for its medicinal properties. According to several Puranas, Lord Vishnu, who woke up from cosmic sleep on Uthana Ekadashi (the day before ksheerabdi dwadasi), comes to Vrindavan or Brundavan along with Goddess Lakshmi and Lord Brahma. Hence, worshipping Tulasi plant along with Sri Maha Vishnu on this day gives many meritorious results. Those who protect the deepam (diya) lightened by others will also get good benefits. Tulsi Damodar Vivah is done today in most of the places. To me lighting many deepams near Tulasi plant brings solace, the practice I have seen and adopted observing my grandmother since my middle school days.(Below is a classic song on Tulasi plant rarely seen in today's world)
Karthika pournami (full moon day) (November 10) in the month of Karthika, is the most auspicious day of the most auspicious month. This day is celebrated with great enthusiasm and devotion. Many Hindus consider fasting on this if they could not fast on any other auspicious day in this month. Devotees also make it a point to take a holy dip in the sacred rivers. In the evening prayers are offered to Moon God, 365 wicks are immersed in ghee or sesame oil and are lit in the home altar or in the temple. In the temple arena, lights are lit in rows and hung on stands representing as ‘jwala thoranam’ (lighted garland). Later the cooked food is offered to God and prasadam is taken.