Why do people worship the Tulasi plant?
"Tulasi is auspicious in all respects. Simply by seeing, simply by touching, simply by remembering, simply by praying to, simply by bowing before, simply by hearing about, or simply by sowing this tree, there is always auspiciousness. Anyone who comes in touch with the Tulasi tree in the abovementioned ways lives eternally in the spiritual world."
—Srila Prabhupada, The Nectar of Devotion
Worshiping Krishna’s devotees is an essential feature of devotion to Him. Sometimes great devotees appear in forms other than the human form. One such devotee, whose worship is central to the worship of Krishna, is Tulasi. She serves Krishna in the form of a plant, and devotees worship her in that form. Full of love for Krishna, she can give it to others.
Srimad-Bhagavatam 3.15.19 explains the special position of the Tulasi plant: “Although there are numerous flowering plants full of transcendental fragrance in the spiritual realm, they are aware that Tulasi is given special preference by the Lord, who garlands Himself with Tulasi leaves.”
In her form as a plant, Tulasi always stays at the Lord’s feet and around His neck. (Her leaves and flowers decorate His feet and are strung into garlands to be worn around His neck.) The Vedic scriptures say, “Krishna gives Himself to a devotee who offers Him merely a Tulasi leaf and a palmful of water.”
The wood of dead Tulasi plants is used to carve sacred beads devotees wear around their necks and use for chanting the Hare Krishna mantra.
Tulasi is always grown at Krishna temples. Like the deity, she is offered arati. Many devotees of Krishna keep and worship Tulasi at home.