Answer: Bananas are fast-growing tropical plants. Their tops can be damaged or killed back by prolonged frosts but their roots are relatively hardy. If the tops are killed down, new sprouts generally develop the following spring. While I can appreciate trying to save the tops of your plants, it might be better to cut them down to ground level and place a protective mulch over the root area. Sometimes the winters in Seattle are warm and wet, sometimes they're cold and snowy. You can wait to see what the winter brings, cutting the tops down after a killing frost if necessary, and leaving them alone if it's warm and wet. If the trees are relatively small you could construct a protective cover over them, but you'd want to make sure fresh air circulates within or the leaves will turn to mush and you'll be no further ahead than if you cut the tops off at ground level. I think I'd be inclined to allow the plants to remain as is, see what the weather brings, and react accordingly. Hope this sheds some light on your banana quandry!
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