Answer: You are really lucky to have your Elephant's ears overwinter in Delaware! They are tropical plants! I'd recommend digging the tubers and storing them over the winter months. When temperatures get cold the foliage will die back. At that point, cut off the dead foliage, dig the tubers, brush off excess soil, and store the tubers in dry peat moss over the winter months. You may find that the tubers have developed outgrowths. If so, you can break them off in the spring and plant them on their own. Coreopsis is difficult to divide because they typically grow only one main stem. I think I'd simply move the entire plant rather than trying to split it.
Best wishes with your garden!
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