There are two different points of view on whether to cut back perennials in the fall or whether to leave them alone.
Cut Them Back And Remove Them From The Garden
This leaves the garden neat and tidy going into the winter. All seed heads are put into the compost or shaken off the plants to germinate the following spring.
But your garden does not attract or feed overwintering birds.
Some gardeners do it because they believe it removes any diseased stems/leaves from the garden. In my opinion this is highly overrated as a reason. If you’re paying attention, any serious problems have already been pruned out and removed.
And common fungal problems such as botrytis (the gray fuzz on decaying leaves or black spots on peony leaves) is one of the most common fungi in the world and you won’t ever reduce or eliminate it on susceptible plants.
Leave Them Alone To Winter In The Garden
Doing this allows the seed heads to feed the birds. Any they miss will germinate the following spring.
It’s far less work but it’s not neat and tidy until later in the winter when the stems fall over naturally.
In my opinion, you do whatever seems right – but you do have to do this at some point.