International Flower Bulb Centre
Plant Common Name
Nothing beats dahlias as everblooming warm season bedding plants and cut flowers.
Named for Swedish botanist and student of Linnaeus, Anders Dahl (1751 to 1789), this genus in the daisy family consists of over 30-species, many more subspecies and varieties and literally thousands of cultivated varieties. All are herbaceous tender perennials with bulbous underground tuberous roots, which are colloquially referred to as "tubers" even though the term is botanically incorrect.
Originating from regions in Mexico and South and Central America, Dahlias were revered by native tribe’s people, such as the Aztecs, for decoration, food and medicine. New world collection trips brought dahlias to Europe in the 17th and 18th centuries. Initially, they were entertained as food plants, but this did not succeed, and by the early 19th century ornamental varieties began to appear. In the late 19th century some tubers were shipped from Mexico to the Netherlands and only one survived; that of the colorful red-flowered Dahlia juarezii. This plant was bred and selected with other previously collected Dahlia species, which resulted in the dazzling array of different sizes and floral forms and colors. In fact, these are parents to almost all Dahlia cultivars on the market today.
Most dahlias are bushy plants, of varying sizes, and have deeply lobed leaves in shades of green and sometimes burgundy and dark purple. They are carefully organized into groups defined by floral size and floral form.
Dahlia floral size chart as defined by The American Dahlia Society:
AA: Giant, plate-sized flowers that exceed 10-inches (25.4 cm)
A: Large flowers over 8 to 10 inches (25.4 to 20.3 cm) in diameter
B: Medium flowers that exceed 6 to 8 inches (20.3 to 15.2 cm) in diameter
BB: Small flowers that exceed 4 to 6 inches (15.2 to 10.2 cm) in diameter
M: Miniature flowers that reach 4 inches (10.2 cm) in diameter
BA: Ball-shaped flowers over 3.5 inches (8.9 cm) in diameter
MB: Miniature ball-shaped flowers that exceed 2 to 3.5 (5.1 to 8.9 cm) inches in diameter
P: Pompon-shaped flowers that reach 2 inches (5.1 cm) in diameter
MS: Single blooms, called mignon single dahlias, that reach 2 inches (5.1 cm) in diameter
The 18 Dahlia floral form classifications as recognized by The American Dahlia Society:
Formal Decorative: petals are double, uniformly distributed, flattened, with edges that roll upward or backward and often curve down towards the stem.
Informal Decorative: petals are double, irregularly distributed, not flattened but wavy, twisted, or curly and may roll backward.
Semi-Cactus: petals are double, broad at the base, straight, curving inward or backward and have tips that roll back to nearly half their length.
Straight Cactus: petals are double, uniformly radiate in all directions from the center of the flower, are rolled inward more than half of their length and may be pointed, straight, or curved backwards.
Incurved Cactus: pointed petals are double, curve towards the flower’s center and are curved for more than one half of their length.
Laciniated: double flowers have individual petals that are split at the tips and often twist giving and irregular fringed look to the flower.
Ball: flowers are tight, fully double, and ball-shaped—occasionally with a flattened at the face. The petals are rounded, blunt or indented, sometimes rolled inward and commonly in a spiral display.
Miniature Ball: smaller ball-type.
Pompon: flowers are tight, fully double and similar to ball dahlias but fully rounded and smaller. The petals tightly curve upwards along the edges.
Stellar: flowers are double and have smaller, less developed petals towards the center that graduate to fully developed outer petals. Petal edges curve upwards and outer petals are narrower and lightly curve back towards the stem. Flower depth should be one half to two thirds of the diameter of the bloom.
Waterlily: flowers are double, symmetrical and flattened when viewed from the side. The petals are broad and flowers open with those in the center appearing closed and dome-shaped and those along the exterior being fully developed and slightly cupped.
Peony: flowers are not fully double and have open centers. They have two or more rows of petals that may be straight, broad, twisted or curled. These subtend centers filled with tiny central disc flowers of varying colors.
Anemone: flowers are not fully double and have centers filled with smaller elongated disc flowers of varying colors, which may appear rounded or spiky. They may have one or more rows of out petals that are often broad and open.
Collarette: flowers are not fully double and the opened faced flowers have three tiers of petals. A single row of uniformly flattened, evenly distributed outer petals surround shorter petaloids (approximately one half the length of the outer petals), which surround a small flattened “eye” of disc flowers.
Single: single, open faced blooms with one row of uniform petals surrounding an eye of disc flowers.
Mignon Single: smaller single flowers.
Orchid: flowers are not double but have open centers and a single row of evenly spaced flattened petals surrounding the disc flowers. The petals are rolled inward for two thirds or more of their length.
Novelty Open: flowers are not double but have open centers and unique characteristics which set them apart from other classifications.
Novelty Fully Double: flowers are double but have unique characteristics which set them apart from other classifications.