Dahlias come in a variety of shapes, sizes, colors and forms, some of them so unexpected that the average gardener would not identify them as dahlias. In 2003, there were 18,000 registered dahlia cultivars, further complicating the definition of the flower through the sheer number of specimens under consideration. For this reason, several horticultural societies have conspired to produce a classification system for dahlias, aiding in the identification and organization of the many different cultivars. The system used by the American Dahlia Society takes into consideration the size, form and color of the flower.
Measure the size of the blooms in inches. The American Dahlia Society codes sizes, from largest to smallest, as AA, A, BB, B, M and P, beginning at 10 inches or larger and decreasing in increments of 2 inches.
Find the appropriate size code on the right-most column on the classification chart.
Identify the flower form. Form takes into consideration many factors, including the shape of the flower in general (flat or ball-shaped), the shape and curling of the petals, the arrangement of the petals and the size and prominence of the center of the flower. The American Dahlia Society also uses codes to abbreviate forms. For example, pompon flowers are identified as "P," while collarette flowers are identified as "CO."
Find the appropriate flower form beside the size that you selected. If you do not find the flower form under the size, look to the bottom of the chart, where some forms are listed independent of size.
Describe the color of the flower. Dahlias come in solid colors, as well as blended and variegated forms, and the American Dahlia Society has codes for each of these. Color codes tend to include ranges of colors. For example, a dahlia identified as "W" for white may be cream or ivory colored. Furthermore, the color identified is the predominant color on the face of the flower petal, not the underside or small traces of color found on the petal. Find the correct code and locate it on the top row of the classification chart.
Trace your finger from the size and form you identified to the column for the color that you identified. Where the row and column intersect, you will find the type of dahlia that you are trying to identify.