Dahlia Classifications

The official Royal Horticultural Society (RHS) and American Dahlia Society (ADS) use a nearly identical classification system, with the RHS having 14 categories and the ADS having at least 14 (with more if counting the miniature forms). What follows are the different categories, and a description and examples of each type. Also included are a few common, informal grouping terms.

Dahlias come in many forms including prim and proper formal decoratives, the devil-may-care informal decorative, lollipop-like pompoms, and the star-shaped cactus varieties. In addition to the "forms" listed below, dahlia blooms are organized into 9 bloom sizes (with diameters as large as 16 inches or more), and 15 colour groups including blends, variegated and bicolours. There is a form, colour, and size to suit every taste.

Formal Decorative Dahlias

[All Decorative are RHS group 5 (D), ADS (FD), (ID)]Petals generally flat, broad & smooth in a regular arrangement that gradually recurve toward the stem.. An example of a decorative dahlia is ‘Berliner Kleene’ (Decorative).More photos of formal decorative dahlias

Informal Decorative Dahlias

[All Decorative are RHS group 5 (D), ADS (FD), (ID)]Petals generally twisted, curled or wavy, of uniform size in irregular arrangement. May be involute or revolute. An example of an informal decorative dahlia is 'Bodacious.'

Semi-Cactus Dahlias

[RHS group 9 (S-C), ADS (included as part of the cactus group)]These resemble cactus dahlias but have very pointed petals that begin flat and roll for half their length. They thus give both a spikier and fluffier appearance than cactus dahlias. An example of a semi-cactus dahlia is ‘Tahiti Sunrise’.

Straight Cactus Dahlias

[RHS group 8 (C), ADS (C), (IC), (SC)]These have long, narrow petals in double blooms that have a spiked ball appearance. The petals are often incurved (IC) or straight (SC). An example of a cactus dahlia is ‘Bora Bora’.

Incurved Cactus

Petals pointed, narrow at base, uniform in length, curving upward toward the bloom face, or swirl horizontally. An example is 'Bright Star.'

Laciniated Dahlias

[RHS group 11 (Fimbriated)]The petals of these dahlias may be straight, curved, incurved, flat, or twisted. What sets them apart is how the petals are divided into multiple sections, giving the flowers a fringed (fimbriated) appearance. ‘Marlene Joy’ is an excellent example of a fimbriated dahlia.

Ball Dahlias

[RHS group 6 (Ba), ADS (BA), and (MB)]Ball-shaped double blooms of formed, incurved petals following a spiral pattern. The tips may be rounded, flat, or indented, while the ball may be round or slightly flattened. An example of a ball dahlia is ‘Jomanda’.More photos of ball dahlias

Miniature Ball

Same as ball, except smaller, between 2-3.5 inches in diameter. 'Lady in Red' is a great miniature ball dahlia.

Pompon Dahlias

[RHS group 7 (Pom), ADS (P)]These are globe-shaped double flowers with inward-curving petals which may be blunt or rounded. They tend to be small in size and symmetrical. An example of a pompon dahlia is ‘Burlesca’.

Stellar Dahlias

Ray Florettes are long and narrow along their length with pointy tips preferred. All the ray florettes will have a partially involute form recurving toward the stem. This example is 'Alloway Candy.'

Waterlily Dahlias

[RHS group 4 (WL), ADS (WL)]Boasting double, symmetrical blooms, the petals on waterlily dahlias have a slightly cupped to flat shape and tend to be only about half as deep as they are across. An example of a waterlily dahlia is ‘Taratahi Ruby’.

Novelty Fully Double

Distinctly different from other forms with good symmetry, tight closed center, with petals arranged differentlyfrom other forms. This example is 'Pink Giraffe.'

Peony Dahlias

[RHS group 14 (P)]These flowers boast 2 to 5 layers of irregularly spaced ray petals around a central disc. ‘Bishop of Llandaff’ and ‘Fascination’ are two examples of peony-flowered dahlias.

Anemone Dahlias

[RHS group 2 (Anem), ADS (AE)]A central mass of dense, tubular petals ringed by one or more rings of flat ray florets that may be bicolor or solid. Often, the two petal types have contrasting colors, and the flower lacks a central disc. An example of a anemone dahlia is ‘Boogie Woogie’.More photos of anemone dahlias

Novelty Open

The Novelty Open Center Dahlia category is comprised of unique varieties with visible open disc centers surrounded by outer rings of petals. Including this dahlia, 'Hy Zizzle', this type includes varieties that don’t fit into the more structured category types.

Collarette Dahlias

[RHS group 3 (Col), ADS (CO)]Flat flower with a single ring of ray florets and a central disc. Sometimes a smaller inner ring of florets is present, leading to a collar-like appearance. An example of a collarette dahlia is ‘Apple Blossom’.More photos of collarette dahlias

Orchid Dahlia

[RHS group 12 (SinO)]These flowers have a central disc surrounded by a single layer of ray petals which may curve inwards or outwards. 'Verrone's Obsidian' boasts nearly black, windmill-like flowers with sunny yellow centres.

Single Dahlia

[RHS group 1 (Sin), ADS (S)]Perhaps the most simplistic in appearance, single dahlias have a central disc with a single outer ring of ray florets that may be rounded, pointed, and/or overlap. Their more basic design makes them highly attractive to pollinators. An example of a single dahlia is ‘Bishop of York’.

Mignon Single

Same formation as single dahlias except that they have round petal tips and are under two inches in diameter. This is 'Pulp Fiction.'

Dinnerplate Dahlias

Nurseries and growers commonly use this term to describe any dahlia with blooms measuring larger than a dinner plate (i.e., 8″ inches across). ‘Gitts Perfection’ is a good example of a decorative dahlia considered a dinner plate dahlia.

Border Dahlias

While not an official type, the ADS uses the terms “border dahlia” and “container dahlia” to describe dahlias that are generally a smaller 12 to 20″ inches tall. These dahlias may belong to any group but tend to include any dahlia with a smaller, more compact growth habit that would make them suitable as potted Dahlias. The Gallery series is an example of border dahlias.

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