Coleus is a good plant to start with
When it comes to plants that bridge the gap between summer and fall, a favorite of mine is coleus. While technically too sensitive to withstand the really cold days ahead, in shades of deep red, purple, green, orange, and brown, plants look tailor made for early autumn, and provide a lovely backdrop for mums,pansies, and ornamental kale. I pot up coleus seedlings in spring, in containers with petunias, impatiens, or caladiums– whatever you like!
Ornamental kale, salvia and coreopsis (Photo by Sarah Marcheschi)
Come fall, when I replace the warm weather plants with cold hardy selections, the detailed leaves of coleus look just as handsome alongside them. They thrive in the shadier spots in my yard, but also do well in part sun. Plants should be pinched back throughout the season to maintain the best form, and prevent the formation of flowers. (Once the plants flower, appearance of the leaves can suffer, as much of their energy goes into producing seeds.) Making sure to grow coleus in pots and soil with good drainage will help guarantee your plants are still healthy and thriving at the end of the season.
Why not sdd some grass (Sedge) to your fall pots?
Grasses are another group of plants that can be successfully transitioned from summer containers into fall, and Carex, (or Sedge), is one genus that particularly thrives in pots. Sedges are easy to grow, durable, and require little in the way of maintenance. And with around 1,000 species, and many cultivars to choose from, there really is something for everybody. Leaves can be cascading or upright, tall or short, green, or variegated- even bronze colored! Plants do well in shade or sun, and thrive with regular watering and feeding during the growing season. With proper care, these should keep containers looking good through the fall.