Russ1
Yamadori
I find a big factor in overwintering trees outdoors is the wind. Windchill and the drying effect of the wind is the big issue. I'm in zone 6b and have lost maples in pots due to the windchill.
So protect the tree from wind. Take 10 deg F off the hardyness of a tree when in a pot. My first couple years of Bonsai I would put small trees in a covered 5 gal pail with holes in the bottom for drainage and placed the tree on a brick or something to raise it off the bottom. You can leave it uncovered until it loses it's leaves or they are not green any longer. They won't need light then. Keep it in a shaded spot so it doesn't heat up from the sun on warm days. You could also insulate it to keep the temp more consistent. For lighting inside I've been using cheap 48 inch shop lights for many years. 5k bulbs are the best but anything works. I have been changing to cheap $24.00 LED 5k, 4800 lumen lights in the last few years. A humidifier in the room is a big part of keeping the trees healthy, I try to keep the humidity level more than 40% and around 45%. I have found that much higher than 50% and you can create condensation on the windows and mold. I am growing Brazilian Rain Trees, Portulacaria afra, Ficus Benjamina, Ficus Nerifolia, Christmas Cactus, and a half dozen varieties or so of Orchids etc. Too low of humidity and you will get pest like Spider mites. I let the temps in the room get down into the low 60's (F). until around late Dec. (this actually helps the Orchids Bloom) and gives everything a slightly dormant (rest period). Trying to keep it too warm will just dry everything out and lower the humidity. I have placed larger Portulacaria and Ficus more than a foot away, next to the lights because of lack of room under the lights and they have done just fine.. Remember that watering needs will go down during this period unless your humidity is too low.
So protect the tree from wind. Take 10 deg F off the hardyness of a tree when in a pot. My first couple years of Bonsai I would put small trees in a covered 5 gal pail with holes in the bottom for drainage and placed the tree on a brick or something to raise it off the bottom. You can leave it uncovered until it loses it's leaves or they are not green any longer. They won't need light then. Keep it in a shaded spot so it doesn't heat up from the sun on warm days. You could also insulate it to keep the temp more consistent. For lighting inside I've been using cheap 48 inch shop lights for many years. 5k bulbs are the best but anything works. I have been changing to cheap $24.00 LED 5k, 4800 lumen lights in the last few years. A humidifier in the room is a big part of keeping the trees healthy, I try to keep the humidity level more than 40% and around 45%. I have found that much higher than 50% and you can create condensation on the windows and mold. I am growing Brazilian Rain Trees, Portulacaria afra, Ficus Benjamina, Ficus Nerifolia, Christmas Cactus, and a half dozen varieties or so of Orchids etc. Too low of humidity and you will get pest like Spider mites. I let the temps in the room get down into the low 60's (F). until around late Dec. (this actually helps the Orchids Bloom) and gives everything a slightly dormant (rest period). Trying to keep it too warm will just dry everything out and lower the humidity. I have placed larger Portulacaria and Ficus more than a foot away, next to the lights because of lack of room under the lights and they have done just fine.. Remember that watering needs will go down during this period unless your humidity is too low.
