During the winter, bonsai typically have to be stored to protect them from from the wind and from temperature fluctuations. The cold isn’t so much the problem: trees that live in cold climates are designed to survive the cold. The wind, though, can desiccate (dry out) a tree’s tissues, and temperature fluctuations can cause repeated freezing and thawing that can damage pots.
There are several strategies for dealing with these issues. Deciduous trees can be stored in an unheated room or garage. Once they’ve lost their leaves for the winter, they don’t need sunlight. Due to lack of space, however, I have typically placed the trees under their benches and surrounded them with sheets of plastic to keep the wind at bay. More recently, I’ve removed the shelving and simply placed the trees together, and used tall metal stakes to support the windbreak.
I generally put the trees into storage this way over the Thanksgiving weekend, as in my area that’s when temperatures are starting to get low enough that the trees will need some protection. I put them back up on the benches in the early weeks of spring, depending upon how warm it’s getting. This year I left them down a bit longer than usual, because the weather has been unusual. As of today, however, they are back up.
I haven’t started repotting yet, although by all rights I probably should have done so a few weeks ago. Unfortunately, I haven’t had time. With luck I can get to that shortly.