There is nothing simple about dahlia. Some are short bedding plants that behave as annuals. Tree dahlias develop big and lanky canes that can get as high as ground floor eaves, only to replace them during the next summer. The most popular dahlias are lushly foliated perennials with striking and extraordinarily colorful bloom. Most are taller than bedding dahlias, but less than six feet tall.
Dahlias can bloom just about any color except blue. However, most purple dahlias tend to be rather reddish or pinkish. Green dahlias are rare, and tend to be rather yellowish. Floral form is wildly variable! So is floral size. Some dahlia flowers get no wider than two inches. Larger sorts get about ten inches wide, so must be staked. Dahlias might be as variable as related chrysanthemums.
Dormant dahlia tubers can go into the garden as early as late autumn here. Most start in winter though, to be less susceptible to rot while waiting for spring. After blooming through summer, dahlia growth succumbs to frost late in autumn. Division of crowded dormant tubers every few years promotes healthier spring regeneration. There is no need to dig and store tubers through winter here.