I'm starting most of my seeds in my hobby greenhse this year. But I've been confused in past about heat. I use bottom heat to germinate, and then take them off of heat and under lights, plus ambient light, to grow on. During the day temps can climb into the 90's inside, so I open a vent and turn the fan on. At night however, it often dips below zero outside. I do have a heater, but even that only allows the temps inside the greenhouse to get up to 45. Should I put bottom heat back on for the nights? Or should I just let them work thru the temp swings on their own, making sure that they don't freeze?