Answer: Some cold climate hosta hybridizers keep their seedlings growing all year round in (heated) greenhouses, so it is possible to keep them in foliage all winter. I suspect however that the foliage would weaken if grown under normal houseplant conditions and would require very careful reconditioning prior to being moved back outdoors. You might experiment a bit and see what happens. If you keep some outdoors, either plant them in the ground, sink the pots in the ground, or set them in a sheltered spot with insulation around the root zones -- hostas are very cold hardy perennials and should overwinter just fine outdoors. Incidentally, the term tender perennial is usually used to refer to plants that are perennial (live three years or more) in warm climates but will not withstand cold temperatures.
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