Although the most widely available mums are grown as fall annuals, there are varieties that can also be grown as perennials in some regions with a little care to over-winter them. In colder zones, leave the top growth in place and add loose mulch such as straw or evergreen branches around them for protection, waiting to cut back in spring after new growth emerges. In warmer winter climates, they can be cut back to 6” tall after flowering. Check your local garden center to see what varieties work best in your area.