No one can pinpoint when the frost and snow will come. Many gardens survive just fine with no attention at all in the fall. This listing can serve as a guideline, but all gardens are unique. What works for one, may not work for another. It never hurts to take some time and put your garden to bed in the fall.
Some perennials do not handle rough weather well. They will not remain attractive after frost, and they have recurrent problems with pests and diseases, which will overwinter in their fallen foliage and surface in the spring. These perennial flowers are best cut down in the fall. If they are diseased, throw the foliage away, do not even compost it. There will always be exceptions and time will play a factor.
Here are three more perennials to be cut back in the fall.
Beebalm (Monarda didyma)
Even the most resistant varieties of Monarda can succumb to mildew. When that happens, you will be cutting them back long before fall. Fresh, new growth can be left on until spring. Sometimes selective thinning of the stems is all that is needed and you can leave the remaining seed heads for the birds. It grows best in USDA zones 4 through 9.
For your information. If you this summer in some of the Iowa Fields have seen a light purple blooms on areas that isn't growing corn or beans. I found out it was Monarda. Butterflies love these so what a good conservation practice that is. I bet the bees like it also.
Beebalm belongs to the mint family with that square stem. All mints have square stems so easy to identify.
Blackberry lily (Belamcanda chinensis)
Prune to keep the foliage from collapsing and causing the crown to rot and to avoid borers. It grows best in USDA zones 5 through 10.
Blanket flower (Gaillardia x grandiflora)
Gaillardia is a pretty hardy plant, but cutting back the spent stems seems to improve its hardiness even more by improving its vigor. It grows best in USDA zones 3 through 10.
taken from taken from https://www.thespruce.com/perennial-plants-to-cut-back-in-the-fall till next time this is Becky Litterer, Becky's Greenhouse Dougherty Iowa email@example.com