November 28th.
Due to the relatively warm temps we've had all the bonsai are still in the garage. On days that are above 32ºF I open the doors and get some air circuation in there. They have frozen a couple of times. We have had temps as low as 13ºF already. Trident maple is the most root tender bonsai I have.
It's time to move them into their permanent Winter quarters but the weather forcast for this week is for temps in the 30's during the days and teens at night so I'm leaving them in garage until the following week depending on the forcast.
They will be moved into a 12'x 12' unheated room on tables and shelves, junipers on the floor, under the tables. Tridents and Japanese maples go up high because they are the most tender.
Zelkovas, Ginkgos, Hornbeams, Amelancier, JW Pine, and others occupy the tables that are 3' off the floor.
The shades of the windows are drawn half way open allowing some light but not too much. Evergreens are placed nearer the light.
A minimum/maximum hangs from a shelf, 5' off the floor where the Tridents are.
A space heater will be used when the outside temps fall below around 10ºF.
I have the space heater marked as to where to set it for various temperatures that keep it a pretty constant 28ºF give or take a few degrees.
I don't want it getting close to the root killing temp of 23ºF for Trident maples.
I don't have to water until March. I use snow during the Winter and it melts and evaporates to keep the humidity up to snuff.
I mist during really cold spells because the air gets dry. The mist freezes on the plants. I like it when the humidity is such that you can see your breath when you walk into the room.
The coldest they have seen, with this setup, was -45ºF.
There's mark on the space heater for that -45º and I hope I don't have to use it this Winter. I haven't had to since 1992.
I've been using this setup for going on 21 years with success.
Good luck to everyone getting through this Winter!