Answer: Once frost has killed back the foliage, you may leave it alone until spring or trim it off and remove it. Many gardeners will remove it from the garden to avoid harboring pests and diseases over the winter. On the other hand, the old stems will add a bit of insulating mulch to the beds, and that's why some gardeners might opt to leave healthy ones in place until spring. In spring, you would remove all the old stems.
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