Lowest temps plants can grow in? Daytime/Night.

Hey my plants are not gonna finish in time and I'm gonna be moving them indoors to finish. But to avoid the electric bill I'm putting that off for as long as possible. So my question is how cold can it be outside for the plants to still grow? I like a little purpling (if that's even a word) so that's not an issue for me. Anyone's advice is appreciated but anyone from New England is really what I'm looking for. Thanks in advance

its better to move them in now, then suffer from humidity issues and mold and all the other crap that follows from leaving them outside.