Answer: In my garden I leave the foliage on perennials until the frost kills them back, i.e., they wither and brown. It is important to leave the foliage intact while it is still green so the root system can store up enough food energy for the long hibernation. I then cut them back to a height of 3". I do not cut back my Black Eyed Susans for the simple reason that I like the way their little "heads" look covered in snow on an otherwise dreary winter landscape. Mulching is not necessary, but if you wish to do so, apply a light, airy mulch such as pine boughs after the ground freezes.
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