Answer: Japanese maples are rated as hardy to zone 5b. As a rule, container-grown plants lose one zone of hardiness so container-grown Japanese maples are really rated for zone 6b. Just to ensure survival you should protect them in winter by plunging the pot in the ground or covering the pots in leaves for extra insulation. Although you can overwinter potted maples in an unheated garage or shed, as long as the temperature does not drop below -10, it shouldn't be necessary as your zone generally doesn't get that cold. I think I'd either sink the pot into the ground, or set them on the ground (not on a deck or patio) and pile leaves over them to insulate them from the cold.
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