Dahlia Forms, Sizes and Colors

Nineteen forms of Dahlias have been defined as classes by the American Dahlia Society. Several of these categories are further divided into five size ranges from Miniature to Giant. These divisions are subdivided further into 15 color categories. There are over approximately 570 individual Dahlia classes. It has been estimated that there are over 40,000 named Dahlia varieties, a testament to the development efforts for this remarkable flower over the years.

In the late 19th and early 20th centuries, the dahlia was the second most popular flower in the U.S. after the rose. The popularity of the Dahlia is coming back as a result of the vastly improved quality of individual flowers and the larger number of sizes, colors and forms.

Dahlia Forms

Formal Decorative-Petals are generally flat, broad, and smooth in a regular arrangement that gradually recurve toward the stem. Each petal row should convey uniform and regular size arrangement with the tips preferably round or extending to a slight point. The ideal depth is 3/4  the diameter of the bloom.		Waterlily-The bloom should be fully double and symmetrical. The side view should be flat to saucer-shaped in arrangement, and the layer of petals should be open faced to give a delicate appearance. The center should be closed and dome-shaped breaking gradually to four to seven rows of fully developed outer florets. Outer petals should be broad and slightly cupped. Depth is less than 1/2 the diameter.
Informal Decorative- Petals  are twisted, curled or wavy, and of uniform size in irregular arrangement. They may be partially involute (curving in) or revolute (curving back), but not portion should be fully revolute or involute except at the tip of  the petal. The ideal depth is 3/4 the diameter of the bloom.		Peony-An open centered dahlia with two or more rows of ray florets surrounding the disc flowers which are small tubular florets which make up the central part of the flower.  Ray florets adjacent to the disc flowers may be smaller, twisted, and/or curled.
Semi-Cactus- The petals are broad at the base, straight or incurved, and reflex toward the stem in a regular and uniform arrangement. Petals will be revolute for approximately half their length and fully revolute (touching or overlapping) for at least 1/4 of their length.  The ideal depth is 3/4 of the diameter of the bloom.		Anemone-Dahlias with one or more rows of ray florets surrounding a center of elongated tubular disc florets. The outer petals should be equal in shape, size, and formation, generally flat with rounded tips, and regularly arranged around teh disc florets. The tubular disc florets should be fully developed and present a domed, pincushion appearance
Straight Cactus- Petals are narrow at the base, straight, uniform in length and reflex toward the stem, radiating uniformly in all directions from the center. They will be revolute for the majority of their length and full revolute for approximately half their length. A depth of about 3/4 the diameter is ideal.		Collarette-A bloom will have single row of flat or slightly cupped ray petals arranged in a flat plane. The ray petals will uniformly overlap, with no gaps. The petaloids surrounding the disc should be approximately 1/2 to 2/3 the length of the ray florets. Eight ray florets is preferred. The disc should contain evidence of pollen.
Incurved Cactus- Petals are pointed, uniform in length, the petal ends uniformly curve toward the face of the bloom, are revolute for the majority of their length and are fully revolute for at least half their length. Because ray florets curve toward the face of the bloom, they usually lack the depth of the preceding dahlia forms.		Single-The bloom has a single row of flat or slightly cupped ray florets arranged in a flat plane. They uniformly overlap with no gaps. Eight ray florets are preferred. Disc flowers with up to three rows of pollen are preferred. Ray floret tips should be rounded, and the bloom is over 2" in diameter.
Laciniated - Petals are split at the tip. The number and depth of the splits may vary. The splits should uniformly twist or curl whether involute or revolute. The majority of ray florets should be uniformly arranged with a split, twist or curl that conveys an overall fringed or frilled effect. Petals with a shallow notch are not classified lanciniated.		Mignon Single-Same as single dahlias, generally with even more rounded ray floret tips. The blooms are under 2" in diameter.
Ball-Blooms are ball shaped with uniform petal, involute for most of their length, and fully involute for more than half the length. The petals reflex toward the stem. Petals in cross section should be circular and exhibit little distortion, completely filling the floral head and are either round or blunt with notch or point.		Orchid-An open centered dahlia with a single row of evenly spaced ray florets in a flat plain surrounding the disc flowers. The ray florets are involute for 2/3's or more of their length and fully involute for at least 1/3 of their length. Eight ray florets are preferable. The disc should have up to three rows of pollen.
Miniature Ball- Same as the ball dahlia except for size, which is smaller at 2" to 3.5".		Novelty Open-Dahlias with characteristics distinct and different from the present classifications. These dahlias have an open disc center with pollen.
Pompon-Same generally as the ball dahlia description, except that the diameter is less than 2".		Novelty Fully Double-Dahlias with characteristics distinct and different from the present classifications. These varieties will  be fully double and have a closed center.
Stellar-Petals break gradually from immature petals to fully developed outer ray florets. The outer petals should be narrow and involute with a slight recurve to the stem. The less mature petals should possess the same narrow and partially involute characteristic. The depth should be 1/2 to 2/3 the diameter of the bloom, with greater depth being ideal.		These  form definitions are adapted from the 2005 Classification and Handbook of Dahlias, published by the American Dahlia Society. As Dahlias continue to be developed, it is entirely possible that new forms will be defined as a class for shows. The stellar dahlia is an attractive form of dahlia which became a class in the last decade.

Dahlia Size Categories

The following Size Categories apply to Formal Decorative, Informal Decorative, Semi Cactus, Cactus, Incurved Cactus and Lanciniated Dahlias. In shows, Cactus and Incurved Cactus are combined as one category.

AA -(Giant), over 10 inches in diameter
A -(Large), over 8 to 10 inches in diameter
B -(Medium), over 6 to 8 inches in diameter
BB -(Small), over 4 to 6 inches in diameter
M -(Miniature), up to 4 inches in diameter
 

Other size definitions.

BA -(Ball), over 3.5 inches in diameter
MB -(Miniature Ball), over 2 to 3.5 inches in diameter
P -(Pompon), up to 2 inches in diameter
MS -(Mignon Single), up to 2 inches in diameter
 

Dahlia Color Categories

The ADS recognizes 15 different color or color combinations of dahlias. They
are:

1) White
2) Yellow
3) Orange
4) Pink
5) Dark Pink
6) Red
7) Dark Red
8) Lavender
9) Purple
10) Light Blend - a blending of the lighter tints and tones of pink, yellow,
lavender, and other pastels
11) Bronze
12) Flame
13) Dark Blend
14) Variegated - where two or more colors appear on the face of the bloom either
in dots, splashes, stripes on narrow lines
15) Bicolor - blooms with two distinctly clear and sharply separated colors