Vanabhojanam (Vanbhojan) is a garden party or picnic arranged during Kartika masam in Andhra Pradesh by some organisations and traditional families.
As per Hinduism, plants are very divine aspects of the nature, hence some plants are worshipped as Gods. Tulasi (Ocimum), Usiri (Amla), Bilva and Durva plants are considered as Gods and useful material in Puja.
Kartika Vana mahotsavam is arranged by some organisations just to chant mantras and to awake the spiritual conciousness in children. But, nowadays it has become fully loaded with entertainment like singing and dancing.
It is to note that Telugu Kartika Masam 2018 starts on November 8 and ends on December 7.
There is a popular belief in Hinduism that Lord Vishnu and Goddess Lakshmi along with all the Gods visit and reside under Amla tree and Tulsi plant during kartik month.
Duirng the occasion, people cook food under trees or in parks and eat. Offering puja to Lord Vishnu and other Gods, reciting Vishnu Purana and kartika Purana during Vana mahotsavam is more preferred rituals.