Dahlias are native to the mountain meadows of Mexico and Central America, where their tuberous roots anchor them through dry seasons and their flowers evolved to attract the attention of passing insects. The genus, named for the Swedish botanist Anders Dahl, encompasses 41 accepted species and an almost incomprehensible diversity of cultivated hybrids, recognized by the American Dahlia Society across 29 distinct flower forms: pompon, cactus, decorative, waterlily, collarette, and more. In practice, most of what gardeners grow are complex hybrids of mixed parentage, selected for flower size, color, and season length.

Tuberous roots are cold-sensitive below 25 degrees Fahrenheit, which pushes dahlias into the annual category for much of the country. In zones below 7, the tubers are best lifted in autumn, dried carefully without washing, and stored in barely moist vermiculite or sand at 35 to 45 degrees through winter. Fertile, moist but well-drained soil and a position in full sun to light afternoon shade produces the best results. Taller varieties often need staking, and regular deadheading extends the season from late summer through the first frost. Despite their tropical origins, dahlias can flag during peak summer heat, and consistent moisture and mulch carry them through that mid-season pause.