A thick layer of mulch around perennials can help them survive winter by insulating the roots against cold temperatures

https://www.scribd.com/document/844183923/How-to-Maintain-Your-Landscape-Using-Quality-Hardscaping-Materials-and-Mulch-204948

A thick layer of mulch around perennials can help them survive winter by insulating the roots against cold temperatures and harsh weather conditions.