Dahlias (Dahlia variabilis) can be started in a variety of ways. They can be grown from seeds, started from dormant tuberous roots or purchased as transplants. Dahlias can grow from 1 to 6 feet tall and come in a variety of shapes and sizes. Dahlias begin to bloom in spring and can continue until the first frost. In the late 19th and early 20th centuries, the dahlia was the second-most popular flower in the states after the rose. Its popularity is returning because of the improvement of varieties over the years.
Types of dahlias depend on form, size and flower color. Nineteen forms of dahlias have been defined as classes by the American Dahlia Society (ADS). Some are further divided into five size ranges from miniature to giant. These are then even further divided into 15 color categories and over 570 classes. Form classification has to do with bloom shape and petal arrangement.
Flower Shape and Petals
There are distinct flower shapes and petal arrangements to dahlias. Single-flowering dahlias only have one row of petals and grow at the most to 3 feet. The flowers are 4 inches or less in diameter. Double-flowering dahlias have more than one row of petals, grow taller and have bigger flowers. Some of these types also have tubular shaped petals that curve backward.
There are several types of bloom forms. Examples include: formal decorative (FD), which have petals that are flat, with even and uniform placement; informal decorative (ID), which have flat petals that sometimes slightly roll at the tips and have a non-uniform placement; and anemone, which have one or more rows of flowers around the center. The outer petals are equal in formation and are flat with round tips.
Size and Color
The size classification applies to formal decorative, informal decorative, semi cactus and cactus forms. The size classification is primarily used in flower shows for judging. AA or giant have blooms over 10 inches in diameter. A or large is 8 to 10 inches in diameter. B or medium is 6 to 8 inches in diameter. BB or small is 4 to 6 inches and M or miniature is up to 4 inches in diameter.
The ADS recognizes 15 different color and color combinations of dahlias. They include white, yellow, orange, pink, dark pink, red, dark red, lavender, purple, light blend (a blending of lighter tints of pink, yellow or other pastels), bronze, flame, dark blend, variegated (two or more colors appear on the bloom) and bi-color (two distinct, clearly separate colors).