We will presume, because you asked this question on this page, that the plant is a peony. (If it’s not, disregard the following.) Peonies are perennials but they grow from their root annually. Peony leaves would naturally die back and the stems would naturally shrivel and collapse in the fall, and they would possibly even decay over the winter. So whether you cut it back or not, it dies back. If it is a peony, you can cut it back in the fall.
We will presume, because you asked this question on this page, that the plant is a peony. (If it’s not, disregard the following.) Peonies are perennials but they grow from their root annually. Peony leaves would naturally die back and the stems would naturally shrivel and collapse in the fall, and they would possibly even decay over the winter. So whether you cut it back or not, it dies back. If it is a peony, you can cut it back in the fall.