Mums are the traditional fall flower - but don't stop there. Most ornamental grasses reach their peak in fall. The billowy seed heads add texture and motion to the garden and the seeds of some attract birds.
Shrubs and trees, like redbud add color complementing the surrounding perennials and fading annuals. Cold tolerant pansies and ornamental cabbage and kale can add a fresh splash of color. Plus, the pansies provide nectar for late season butterflies.
Some perennials like calamint continue to bloom into the fall while the Japanese anemone starts its floral display as temperatures cool. Combine them with dwarf conifers, shrubs and annuals with complementary colors and texture.
And don't forget about the fall color on perennials. Often overlooked, the colorful fall foliage of this persicaria and other perennials can add to your fall display.
A bit more information: Leave perennials stand for winter. The seed heads of many provide food for the birds. These no maintenance bird feeders will help attract a variety of birds adding color and motion to the landscape. Many perennials also serve as winter homes to butterfly larvae and chrysalis (cocoons). Use a light touch when cleaning the garden in spring. A little plant debris in the garden may contain the start of a beautiful butterfly population for you to enjoy in summer. Do remove disease and pest infested perennials in the fall. A bit of sanitation goes a long way towards preventing disease and pest problems the following year.