I know this sounds stupid but I'm uncertain. My thanksgiving cactus is starting to bud and she is sitting right next to my Easter cactus. I have been keeping my window open every night for the past few weeks. The tc started budding when we were getting an unexpected warm spell and tonight it will be 4 Celsius (39F). Both sit under my window in my bedroom and I have a temp/hygrometer that I always watch. Some mornings it can be very cold in my room but at least 60% humidity worst case 50% but that hasn't happened yet. I'm worried if it gets too cold the buds may drop but I want my Easter cactus to get the cold treatment. I suppose I could move tc each night to get out of the cold draft but I don't want to if this isn't necessary!