I live in a 4b zone in North America - known for long and cold winters that can get down to sub-0 Fahrenheit for about a week. I have created a maple forest from just baby maples I've collected around my yard. They all currently have their leaves on them and appear to be doing well. However, I am worried about the winter for them. Should I bring them inside and have them under grow lights? If so, when would be the best time for that?

Once they lose the leaves they do not require light, they can be placed in a cold unheated shed or garage not in a house. Growlights are pointless when the trees are dormant. Do not let them dry out completely.