Tulsi, also spelt as Tulasi, is considered as the Hindu Goddess. In fact it is a divine plant as per Hinduism.
Here is the Tulasi stuthi, a prayer to Tulasi mata.
The prayer is chanted during Kartik maas especially during Tulsi Damodar Vivah on Utthana Ekadashi or Ksheerabsi Dwadasi or Kartik purnima.
Sarvamangala mangalye shive sarvartha sadhike
Saranye thryambake tulasi narayani namostuthe //
Padmahastham padmamukhim padmastham padmalochanam
Lakshmiroopa maham vande tulasim amritarupineem //
Mahaushadhi namasthubhyam namasthyubhyam gunodadhe
Haripriye namasthubhyam namasthubhyam krupakari //
o n which day best to pray tulsi
vrandaye tulsi deve priyaye kesvaspche tulasi mata mantra