It might seem that the only color in your yard come fall is in the form of leaves, but with proper plant selection, you can enjoy flowers in September, too. Some flowers are on their last hoorah, having begun blooming in late summer and finishing their show during September. Others don't come into their own until the fall and will continue to bloom until frost puts a stop to it. If you choose well, you will continuously have flowers from late summer through September and beyond.
Depending on where you live, snapdragons will either behave as a perennial or as an annual. The plant produces flowers on spikes that reach up to 4 feet high. Flowers can be white, red, pink, orange or purple. They like to bloom and will continue to do so until a hard frost puts a stop to it.
Belying its name, the showy sunflower ignores the fact of shorter days and continues to bloom in darkening September. The sunflower is golden, sitting atop strong tall stems. Some varieties have heads that are over a foot wide. The heads turn to face the sun as the day progresses.
Anemones are also known as windflowers, with many blooming in the spring. The Japanese anemone (Anemone hupehensis), though, chooses to bloom in late summer and fall. Depending on the plant you choose, the flowers are white, red or pink. With anemone varieties that flower in summer, as well, you could have a bed that provides a show from spring time through harvest time.
You have a lot of varieties to choose from if you intend to plant the perennial flower aster since there are hundreds of species. These possess a wide color palette. Height varies as well, with some growing up to 6 feet tall. Make sure you choose a fall bloomer, because some hybrids have been created to bloom in spring.
As if inspired by the colors of the changing leaves above them, perennial chrysanthemum begins blooming in fall colors come September. Yellow, orange, burgundy--these are common colors for the flower, which many call mum for short. Chrysanthemums are perennials, so start them off right and you'll be able to count on their flowers year after year. Moderate climates can expect mums to blooming into October. Cold climates might have to grow mums as annuals.
Reliable pansies can bloom year after year unless you live in a hot climate. In such places, the flowers might do better as a biennial or even an annual. If you live in a moderate climate, pansies bloom in September, and then might live on through the winter, blooming whenever the weather isn't too harsh. The flowers are up to 3 inches wide, the plant about 8 inches tall maximum. Pansies are edible (petals), can be used as cut flowers and dry well either as pressed flowers or by being dessicated (see Resources).