I put the deciduous plants and trees in my garage over winter where it is very dark but does not quite freeze. I'm in zone 5. But what about the evergreens? Should they be kept where it is lighter or doesn't it matter?
I over-winter more than 75 evergreen bonsai in my garage each winter, and keeping them (practically speaking) in darkness for the duration is no problem. While they are capable of some small degree of photosynthesis and a very small amount of growth during the period of chill, it is so negligible that the elongated growth dark conditions would produce at higher temps is not even a factor.
I move my plants outdoors in spring as soon as I know (mostly night) temperatures are reliably going to be
I move my plants outdoors in spring as soon as I know (mostly night) temperatures are reliably going to be above 25*.
Roots are already growing well while the plant is still in the garage, The warm temperatures there protect even the most succulent roots. Exposing these fine and succulent roots to temperature extremes can cause them to die back. Regenerating the roots is costly from the perspective of the plant's energy outlay, so try to avoid temps much below freezing in spring. Some plants that I want to get good light after they start growing (mostly deciduous material) get put on a farm wagon that I move between outdoors when temperatures allow, and cover when it's too cold. It's a good strategy for these plants because growing them in the garage under low light conditions produces internodes so long it/they can destroy the plant's form. That's not a major concern with evergreens, however.