Dahlias range in size from 5 cm to over 25 cm in diameter. The array of shapes includes formal decorative, informal decorative, semi-cactus, straight-cactus, incurved-cactus, laciniated [a twisted, fringed effect], ball, pompom, stellar, waterlily, peony, anemone, collarette, single [like the original dahlia], orchid, and novelty.
Dahlias display every color but blue and black, but they seem happiest with the warm, rich, velvety colors of autumn: flame and bronze and lavender and yellow.