Catnip is a Mediterranean plant: it thrives best in intense sunlight,
perhaps with shade part of the day) and relative dryness.  There are a
number of plants growing wild around my house, and the strongest are
in (near the ends of) the crack between the asphalt driveway and
concrete patio - this is the worst and driest soil, and hottest
surface available.  Since it is a green plant, it will not grow in the
dark, except to elongate the stems in an effort to find light, and
that only until it runs out of stored energy - constant wetness with
cause the roots to rot. It can be grown under fluorescent lights, but
it's generally not very healthy.

It would be best to put the plant by a window so it can have natual
sunlight. With lots of care the plant could live for many years.
Catnip does very well outdoors planted in the ground here in Indiana,
USA.
It is a perennial and comes back every year and has beautiful white
flowers in the summer.

Ed

Pot it in a HANGING pot (reason obvious) Hang it outdoors
where it can catch the afternoon breeze. Be sure to hang it
somewhere where the neighborhood cats can't get to it. Water
it once or twice a week. Miracle Grow once a month and
you'll have catnip all summer into late fall. I've been
growing it for years. Jerry will try to take my hand off to
get to it. Great stuff.
Dusty