What is the minimum temp for growth?

I live in the northern latitudes and it gets cold here. My plants are indoor grown with natural window light only. Suprisingly, they do well, although I'm sure quite slower than my commrades with fancy lighting. My question is, I have my plants in a room that has no heat and can get quite cold... like 40-50 deg F. during the night.

There is no way to regulate temp to this room, other than to open/close the door. There is no heating duct or anything, and my wife objects to the skunk and also paying to heat a room that is not used except for growing.

I seem to recall someone saying that growing will stop at temps below 54 deg F. I really don't want to add lighting to generate heat.

So my fellow tokers, will my babies grow in that temp range or become dormant?

Proper Growth temp shoulde be 70-80F

and man is that Cold
ur plant will suffer in that cold climate i'll say buy
a real small heater n i mean smallest u can find and just leave it running in the room.....best if u can grow in a small area like a closet since heat will get trapped and stay in there. since it cold where u are..just adjust the heater to about 65 degree F
and the temp should rise n stay a constant 73-76

this is jus a advice ^^ o and if u r goin to grow in the closet the light should be enough to keep room warm if not THEN use the heater xD

ive seen them stop growing below 60,i have had plants veg at 60 without growth.