Oh no, your poor bonsai. I love bonsai. I had a tiny little juniper for a bit. I also attempted my own with a box but put it out one Winter in the ground thinking I'd get to it next year, let's say that box is now 10 feet tall and is clipped as a sphere in my garden every summer. I guess it wanted to be a big topiary more than a bonsai ;) Good luck, stay warm and protect your babies. Can they be wrapped in plastic to increase their humidity and heat like mini greenhouses around each one?