Why Tulsi plant is not kept inside the house....why it is always planted outside .?

Generally Tulasi is kept in the garden but there are times Tulasi is
kept inside sometimes.
Tulasi plant is kept inside the house for sometime during puja. One
has to keep the tulasi in nice pots and then carry with care. Also
tualsi is kept inside the house if the temperature outside is very low
then one can provide temperature by the help of lamps.
Tualsi is kept in portable pots outside and then carried inside for
worship in the temples and houses. There are tualsi puja conducted
with arati and kritan and then finallly everyone circumbulates tulasi
a minimum three or four times. After the arati etc... one waters
tulasi with few drops of water from the acamana patra.
Some of the prayers for tualsi.
Planting, watering, protecting, maintaining, circumambulating, seeing,
bowing down to, praying to, and glorifying are all ways of serving and
worshiping Tulasi and are highly beneficial
Shri Tulasi Pradaksina Mantra
yani kani ca papani
brahma-hatyadikani ca
tani tani pranasyanti
pradaksinah pade pade
Translation: "By the circumambulation of Srimati Tulasi Devi all the
sins that one may have committed are destroyed at every step, even the
sin of killing a brahmana."
Shri Tulasi Pranama
vrndayai tulasi-devyai
priyayai kesavasya ca
krsna-bhakti-prade devi
satyavatyai namo namah
Translation: "I offer my repeated obeisances unto Vrnda, Srimati
Tulasi Devi, who is very dear to Lord Kesava. O goddess, you bestow
devotional service to Lord Krishna and possess the highest truth."
Please chant HARE KRISHNA and be happy.
hare krishna hare krishna
krishna krishna hare hare
hare rama hare rama
rama rama hare hare