I have a small metal greenhouse outside against a south-facing wall. I've been considering using it to transition my more stout seedlings (like my lavender and zinnias), but temperatures here are doing the ol' Indiana rollercoaster. I live at the

What lows (temperature-wise) should I look for at night to know it's safe to leave my seedlings out there? I'm afraid the metal might not insulate well against lows below 50.