Srila Prabhupada on Srimati Tulasi Devi

“Tulasi leaf is very, very dear to Vishnu. All Vishnu-tattva Deities require profusely Tulasi leaves. Lord Vishnu likes garlands of Tulasi leaves. Tulasi leaves mixed with sandalwood pulp and placed on the lotus feet of the Lord is the top most worship. But we must be very careful that Tulasi leaves cannot be placed on the feet of anyone except Lord Vishnu and His different forms. Tulasi leaves cannot be placed even on the lotus feet of Radharani or on the lotus feet of the Spiritual Master. It is entirely reserved for being placed on the lotus feet of Krsna. We can place, however, Tulasi leaves in the hands of Radharani for being placed on the lotus feet of Krsna, as you have seen on the Govinda album.”
I am giving herewith three mantras for Tulasi devi as follows:
Vrndayai tulasi devyai, priyayai kesavasya ca
Vishnu-bhakti-prade devi, satyavatyai namo namah
I offer my repeated obeisances unto Vrnda, Srimati Tulasi Devi, who is very dear to Lord Kesava [Krsna]. O goddess, you bestow devotional service to Krsna and possess the highest truth.
This is offering obeisances, bowing down (pancanga pranam). And when collecting leaves from the plant, the following mantras should be chanted for picking leaves and manjaris:
Tulasi amrta-janmasi, sada tvam kesava-priya
Kesavartham cinomi tvam, varada bhava sobhane
O Tulasi devi, you are born from nectar, and you are always very dear to Lord Kesava. Now in order to worship Lord Kesava I am collecting your leaves and manjaris. Please bestow your mercy upon me.
Then the mantra for circumambulating the Tulasi tree:
Yani kani ca papani, brahma-hatyadikani ca
Tani tani pranasyanti, pradaksinah pade pade
 
By the circumambulation of Shrimati Tulasi Devi all the sins that one may have committed are destroyed at every step, even the sin of killing a brahman.
So there are three mantras, one for bowing down, one for collecting the leaves & one for circumambulation.
The collecting of leaves should be done once in the morning for worshipping and for putting on the plates of foodstuffs to be offered.
On each bowl or plate there should be at least one leaf.
So you follow and practice these Tulasi affairs and you try to distribute your experience to all the other centre’s, that will be a new chapter in the history of the Krsna consciousness movement.
(Srila Prabhupada to Govinda dasi, 7th April, 1970)

No sprays can be used, not at all. The best thing is to simply daily water tulasi devi and keep her clean. Nothing else is required.
(Letter from Srila Prabhupada, July 26, l975, Los Angeles)

Please take care of the tulasi plants in the following way. This is the best season for growing tulasi plants. From 15 April to 15 June is the best season for growing this plant (this is obviously for the Northern Hemisphere!!!). Now I understand that the seedlings are coming out, so the whole spot if possible may be covered by some net because the seedling stage creeepers, being very delicate, are sometimes eaten up by the sparrows, so we have to give a little protection from attack of the sparrows. All the devotees should pour water at least once in the morning before taking prasadam. The watering should not be very much large in quantity, but it should be poured just to keep the ground soft and moist. Sunlight also should be allowed. When the creepers are grown at least 7 inches high, then you can take them out from the planting soil and transplant them in a row in a different place. Then go on watering and they will grow like anything. I think this plant cannot grow in cold countries, but if the plants are dispatched from your place and if the devotees take care of the plant with a little care in a flower pot then it may grow.
(Letter from Srila Prabhupada, April 7, 1970, Los Angeles)