Lord Ganesha has the boon that he will be worshipped first in any auspicious occasion. When we perform lord Ganesha puja, we have put many varieties of flowers, leaves and sweets but Tulsi which is a sacred plant for Hindus is never offered to Ganesha. Tulsi mata is considered as the most holy plant in India but Tulsi is not offered to Ganesha because they are involved in a mutual curse.
The story related to Tulsi mata cursed by lord Ganesha. The daughter of dharma raja, she had a great devotion towards god narayana. Once she was walking along the banks of gangas. Tulsi came across the ashram, where Ganesha sitting in the deep meditation. Ganesha looks very beautiful in that state. Ganpati has complete devotion towards lord Krishna. So, Tulsi Maa was impressed and immediately fell in love with ganpati. She asked Ganesha to marry her.
Lord Ganpati was bachelor that time. So he was not looking for marrying anyone. He only wanted to marry someone which has the same divine qualities like her mother parvati. So Ganesha politely refused Tulsi Mata for marriage. Angry with his rejection, she cursed lord Ganesha saying you will remain as a bachelor for long period.
After hearing his curse, lord Ganpati also turn cursed that she will be married to a demon and the blessings of gods will become a plant. Listening the curse, she realized her mistake and begged to him for forgiveness. Since Ganesha became pleased and said,” you will be regarded as supreme among the plants but you always are unacceptable by me. Saying these words, lord Ganesha left the place.