In the Skanda Purāṇa there is a statement praising the tulasī tree as follows: "Let me offer my respectful obeisances unto the tulasī tree, which can immediately vanquish volumes of sinful activities. Simply by seeing or touching this tree one can become relieved from all distresses and diseases. Simply by offering obeisances to and pouring water on the tulasī tree, one can become freed from the fear of being sent to the court of Yamarāja (the King of death, who punishes the sinful). If someone sows a tulasī tree somewhere, certainly he becomes devoted to Lord Kṛṣṇa. And when the tulasī leaves are offered in devotion at the lotus feet of Kṛṣṇa, there is the full development of love of Godhead."

In India all Hindus, even those not belonging to the Vaiṣṇava group, take special care of the tulasī tree. Even in great cities where it is very difficult to keep a tulasī tree, people are to be found very carefully keeping this plant. They water it and offer obeisances to it, because worship of the tulasī tree is very important in devotional service.

In the Skanda Purāṇa there is another statement about tulasī, as follows: "Tulasī 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 tulasī tree in the above-mentioned ways lives eternally in the Vaikuṇṭha world.
(Nectar of Devotion).

Taking the advice of Śrī Caitanya Mahāprabhu and our spiritual master, Bhaktisiddhānta Sarasvatī Gosvāmī Mahārāja, one can go to any part of the world and instruct people to become devotees of the Lord by following the regulative principles, worshiping the tulasī plant and continuously chanting the Hare Kṛṣṇa mahā-mantra.
(Sri Caitanya Caritamrta---2:24:261---purport).

Prabhupāda: Better than Viṣṇu worship is to worship Vaiṣṇava. Tadīyānām ārādhanam. Tadīyā means His servant, or one who is, or what is in relationship with Him. Just like we areworshiping this plant, Tulasī. We are not worshiping all plants, but because this Tulasī has very intimate connection with Kṛṣṇa and Viṣṇu, therefore we are worshiping. Tadīyānām ārādhanam.
(Room Conversation--New York---4th. July, 1972).