i live in metro dc, and haven't needed to bring mine in...
i will when nighttime lows hit 35.
when you do bring em in, trim back severely. put em in the brightest sun you can spare and keep soil just moist.
btw, the rootless stalks in the supermarkets WILL root. it takes about 2-3 weeks and 3 or 4 water changes. i keep mine on a sunny deck and even with starting them in june, they're 30" tall.
btw, when you crop longleafed herbs like lemon grass or chives for culinary use, snip 1 or a few leaves at the base. when cropping leafy herbs like basil, cut just a little above a growth center