Flowers have always had a special place in Hindu religion. Almost all gods and goddesses have their favourite flowers, and it is said that the smell of flowers speed up the fulfilment of ones wishes. Floral aroma are said to have therapeutic effects on humans as well. Some flowers are not excepted my some of the gods. The fragrance of the flowers have frequencies which attract butterflies and bees. In the same way these frequencies match the frequencies of the deities that are present in our atmosphere. When the two frequencies come together they destroy the negative energy and generate positive energy.
The flowers are chosen by colour and certain attributes that are similar to the deities.
Sri Ganesha is offered red flowers like hibiscus, lotus, rose, jasmine, marigolds. Durva leaves are his favourite, however tulsi leaves are not offered to lord Ganesh. In ‘Padma Purana’ it is stated for lord Ganesha
‘Na tulsya ganadhipam’. Meaning never offer tulsi to lord Ganesha.
Lord shiva is offered the flowers and fruit of thorns apple plants. These are said to be poisonous, and lord shiva is known to have poisoned stuff. Shiva likes white flowers like harsingar, naagkesar, kanaer, kusum, aak and Kush or the blade grass. Among all the others his favourite is wood apple leaves or bel leave. No Puja is complete without bel leaves.
Let me tel you an interesting story about how Ketaki flowers are not expected by lord shiva.
It so happened that in beginning of times lord Vishnu and lord Brahma fought with each other to prove their superiority just when they were about to use deadly weapons and destroy all that was created there appeared a strong bright light and the spud said that whoever is able to find the beginning and end of this ray of light will be the supreme god. They both looked and looked but could not find the source of it. Lord Vishnu excepted his defeat but lord brahma lied that he had found the source and the Ketaki flowers sided with him. Lord shiva appears from the beam of light and cut of and of brahma’s head he was cursed that we will be not worshiped by the people. Shiva then turned to Ketaki flowers and cursed them that they shall never be used to worship shiva.
Another time there was this assura named Jalandhar who was given a boon that depended on his wife’s chastity. Vishnu had to beach tulsi’s chastity so shiva could kill Jalandhar. Outraged tulsi banished shiva from being worshipped by her divine leaves.