Perennials are defined as a plant that comes back every year. They do this in spite of the fact that most perennials die back to the ground every Fall. That's because the roots stay alive over winter. Therefore, protecting the plant's roots is most important.
Many perennials will die if their roots are unprotected from extreme cold-weather temperatures, especially after a dry Fall. Therefore, to reduce the risk of root failure, water your perennials thoroughly at least once in late Fall. Also, roots will rot if they are planted in areas with poor drainage. Areas in which water puddles around the roots are especially detrimental to perennials.
Many perennials die to the ground in the Fall. Whether or not you trim the remaining ones to the ground or not is up to you. Trim them to the ground in the Fall if you prefer a neater landscape. If you like some winter color, go ahead and leave them. Be careful when trimming flowering perennial shrubs. Always follow growers' instructions to avoid trimming off next years buds.
Every perennial species is different. Following growers' instructions is very important to maintaining healthy plants. Following their instructions on when and where to plant, when to trim and fertilize, and the plants water and sun requirements are crucial. Soil conditions and cold hardiness zones are also very important. You may want to create a chart with each plant's requirements to ensure you are following directions.
