In the fall, do I cut the dianthus back or leave them as is over the winter?
Certified GKH Gardening Expert
If you have an annual Dianthus, it will die over the winter so you can either remove them now or remove them next spring, whichever you prefer.
If you have a biennial or perennial Dianthus, do not cut back in the fall. The foliage from this year will help protect the plant's base from winter weather. The best time to prune these plants is just after they flower in the spring, as described in the Dianthus section in this article:
This article has a list of annual and perennial Dianthus varieties: