Hari Om
Lord Ganeshji is always worshipped before commencing any auspicious work or writing a book or doing any ritual or ceremony. It is believed that Lord Ganesha has the power of removing any obstruction. Even Lord Shivji and Lord Vishnuji have worshipped Ganeshji at times to get their work done successfully.
Durva grass and red color jaswanti flower are favorites of Lord Ganeshji. But Tulsi (holy basil) which is a sacred plant for hindus is never offered to Lord Ganeshji. Otherwise, Tulsi is widely used in pooja and ceremonies because it is considered as the most holy plant in india. Tulsi is not offered to Ganesha because they (both Ganeshji and Tulsi) are involved in a mutual curse.

Story behind Tulsi for not being offered to Lord Ganeshji
Tulsi is the daughter of Dharmaraja (God of righteousness). In her youthful days she was a great devotee of Sriman Narayana (Lord Vishnu). Once she was walking along the banks of Ganges, she came across handsome Ganesha sitting in deep meditation on Sri Krishna. As son of Maa Parvathi, Ganesha is very beautiful. Also any person in deep meditation state looks more beautiful with Tejas. So you can visualize the beauty of lord Ganesha in that meditative state. Like Tulsi ma, Ganeshji was also in his prime and of marriageable age and both were devoted to forms of Lord Vishnu. So Tulsi ma immediately fell in love with Lord Ganesha and asked Ganeshji to marry her.
Lord Ganesha was a bachelour (brahamchari) at that time, which is the natural status for any meditator. In meditation one is expected to be aloof and the meditator tries to explore oneself rather than indulging in a relationship or material pursuits. So Lord Ganesha was not looking for marrying anyone. Also Ganeshji only wanted to marry someone who possessed the same divine and wonderful qualities of her mother Parvathi Devi.
So Ganeshji politely refused Tulsi ma for marriage. This broke Tulsi’s heart. Tulsi took this as an insult and she became very angry. In her anger Tulsi ma cursed Ganesha that one day he will get married against his wish of not getting married.
Lord Ganesha also in turn cursed Tulsi that she will be married to an asura (demon) and then under the blessings of the sages (or gods) she would become a plant.
Hearing this curse, Tulsi ma realized her mistake and she pleaded Ganesha for forgiveness and prayed to him with divine hymns. Listening to her sincere prayers, Ganesha became pleased and he said ”You will be regarded as supreme among the plants. All gods will be happy with your fragrance. Lord Vishnu will be specially glad to receive the worship with your leaves. But you will always be avoided by my devotees in their worship or rituals”. saying this, Lord Ganesha left the place.
Later on, as per the curse Tulsi ma married the demon king called ‘shankhachuda’. She was a very devoted wife and they lived happily for many years. Then one day her husband was killed in a battle with gods. Later on after getting the blessings from gods she became Tulsi (holy basil plant).
Tulsi is often and widely planted in the courtyard of hindu households. It is also planted in temples and nandavans . Women often worship Tulsi for auspiciousness or Mangala. Tulsi leaves and Ganga jal are offered to the person while in death bed to add merits for the soul’s journey. Tulsi leaves are never chewed or used in cooking where they are subjected to heat. Tulsi is a very gentle and holy plant. It is advised to add Tulsi leaves in copper pot filled with water and drink the water next day to receive great benefits of both Tulsi and copper. When a Tulsi plant dies, it is immersed into a holy river, but it is never offered to Lord Ganesha though Some scriptures support practice of Tulsi being offered to Sri Ganeshji only on Ganesh Chathurthi day.
GF’ Blessings.