PlantLife Online

Answer

I would recommend moving the pots with your Japanese Maple Seedlings from the garden either close to the house in a protected location or take them into the garage. In order to insure survival through the winter months you need to find a location warm enough to keep the roots from freezing but not too warm. Bringing the maple seedlings indoors is not a good option, the warm temperatures indoors will keep the plant from fully entering dormancy which all deciduous trees need for proper growth. Another option is to plant the seedlings pot and all in the garden, then surround the plants and pot with a thick layer of mulch (Several Inches) for insulation.

Remember even though it's winter you should still water your Japanese Red Maple regularly throughout the winter to stop winter desiccation. Of course if they are receiving rain in the garden this is not necessary.