dwlogo.gif (8261 bytes) THE GROWING WORLD OF DAHLIAS

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The dahlia is a flower of many forms, the master of flower disguise and indeed continues to evolve with new developments around 2006.

In order to help identify the many varieties that have existed, attempts have been made to identify characteristics that would allow the flowers to be categorised. This process formed the basis for classification.

In the early days, most dahlias were species types and single flowered. They were mainly grown by botanists in Europe who identified them by their species names.

Eventually hybrids appeared to give rise to Dahlia variabilis, and this began to give rise to identification problems as some flowers now had several rows of "petals". As a member of the Compositae, the dahlia flower is comprised of disc and ray florets, each a flower in its own right, although most horticulturists describe them as petals of the dahlia flower. Once double and semi double forms appeared, other breaks in formation also arose including the pompon type (like the pompon on the top of a sailor's hat) and the collerette type.

By 1900, a few different types were recognised, based on overall shape or colour. Cactus, pompon, single, show and fancy were included in an NDS Guide of varieties in 1904.

During the 1900's more types appeared and by 1950, provisional classifications were possible, but these differed from country to country.

In 1962, at the International Horticultural Congress in Brussels and subsequently at the Congress in Maryland in 1966 an international group of botanists and dahlia lovers (supported by the British, Dutch and American Dahlia Societies) got together to find a way of classifying dahlias in a way that was acceptable to all, and would last for all time.. In order to do this, major and minor characteristics were identified, and classification became a relatively simple matter. This was published in 1969 by the RHS, who had been appointed as the International Registration Authority for Dahlias. To this day, the International Registrar holds a list of all registered dahlias along with much information about them, and in 2003 it holds some 18000 different cultivars.

So what were the major botanical characteristics they defined?

Issues of colour and size were discounted as these could be arbitrary and open to individual interpretation as well as differing growing conditions and climates, and shape was seen to be the defining characteristic. It was essential that a flowchart or decision table of the classifying characteristics be developed so it was not open to interpretation and thus a firm basis for the classification process was found.

Firstly, is the central disk visible (open centred), or is the flower fully double (ie only ray florets visible at the centre). In the case of open centred, the overall appearance of the bloom was then considered.

Secondly in the case of fully double blooms, the folding of the individual ray florets along their longitudinal axis was considered. It could be flat, involute (ie curling inwards) or revolute (ie curling backwards), or even a mixture of these.

As a minor characteristic, the end of any ray floret may be split into two or more divisions. This characteristic was defined as Fimbriation of the petals, and once a flower is put into the appropriate group, the bloom may be sub-defined on this minor character.

The outcome of the discussions was a classification table that had nine clearly defined groups, and a tenth group to incorporate any varieties that did not fit the characteristics of any of the other nine groups. Many of these groups were sub-divided into a set of diameter sizes which were purely arbitrary, but were essentially <4" for Miniature, <6" for Small, <8" for Medium, <10" for Large, and >10" for Giants.

In 2010, The International Register held a meeting with the NDS and the Dutch Dahlia Authorities to put in place a new agreement that could be propagated around the world. As a result of this, fourteen groups were agreed, modifying the 1966 set.




Single dahlias have blooms with a single outer ring of florets, which may overlap, the centre forming a disc.


Anemone-flowered dahlias have blooms with one or more outer rings of generally flattened ray florets surrounding a dense group of tubular florets, and showing no disc.


Collerette dahlias have blooms with a single outer ring of generally flat ray florets, which must overlap, with a ring of small florets (the collar) the centre forming a disc.


Waterlily dahlias have fully double blooms characterised by broad ray florets that are slightly involute along their length (longitudinal axis) giving a saucer shaped appearance to the bloom. The depth should be not more than one third of the diameter of the bloom.


Decorative dahlias have fully double blooms showing no disc. The ray florets are generally broad and flat and may be involute for no more than 75% of their length (longitudinal axis) or slightly twisted, and usually bluntly pointed


Ball dahlias have fully double blooms, ball shaped or slightly flattened. The ray florets rounded at the tips, with margins spirally arranged and involute for at least 75% of the length of the florets


Pompon dahlias have fully double spherical blooms, with florets largely involute along their length (longitudinal axis).


Cactus dahlias have fully double blooms, the ray florets are usually pointed, the majority narrow and revolute for 65% or more of their length (longitudinal axis) and either straight or incurving.


Semi-Cactus dahlias have fully double blooms; the ray florets are usually pointed and revolute for more than 25% and less than 65% of their length and broad at the base and either straight or incurving.


Any dahlias which do not fall into type 1 9 inclusive and type 11, 12,13 & 14 e.g. Thistle Dahlias, etc. This group includes species dahlias


Fimbriated dahlias have blooms where the tips of the ray florets should be evenly split or notched into two or more divisions, uniformly throughout the bloom to create a fringed overall effect. The petals may be flat, involute, revolute, straight, incurving or twisted.

GROUP 12 - STAR DAHLIAS (formerly Single Orchid)

Star dahlias have blooms with a single outer ring of florets surrounding the disc. Ray florets are uniformly either involute or revolute.


Double Orchid dahlias have fully double blooms showing no disc and have triangular centres. Ray florets are narrowly lance shaped and either involute or revolute.


Paeony dahlias have multiple outer rings of ray florets surrounding a disc, ray florets are flat or slightly involute at base and are flat or are to some extent revolute.

In 2017, The International Register held a meeting with the NDS as a result of which a fifteenth group (STELLAR) was agreed, modifying the 2010 set.


Stellar dahlias have fully double blooms showing no disc. Ray florets are long and narrow along their length with pointed tips preferred,. They have space between the florets in each of the rows, and have a uniform regular arrangement. All ray florets are partially involute, displaying a "U" shaped cross section for the majority of their length. Florets reflex towards the stem and bloom depth should be more than half the diameter and not greater than the diameter

Minor Characteristics

Dwarf bedding dahlias which do not usually exceed 609 mm. (24in.) in height.

Liliput dahlias are of exceptionally short growth habit, do not usually exceed 304 mm. (12in.) in height.

Gallery dahlias indicates that these plants grow up to approx 300mm (12in.) in height, and flowers larger than Lilliput dahlias.


Having determined a classification by shape, an attempt was then made to classify by colour to obtain uniformity of definition around the world.


For the purpose of Colour Classification, all colours, shades, tints hues and combinations thereof found in the cultivated forms of the dahlia have been grouped in the following thirteen classes.

Colour Classification is determined by the predominant colour or colours which appear on the face of the ray florets and in such classification the colour of the reverse of the ray florets is not generally taken into consideration. An exception is made in the case of certain orchid-flowered, pompon or ball dahlias.

In the case of Blended, Bicolours or Variegated varieties the first colour indicated is the dominant colour.



The agreed abbreviation follows the colour.

The numbers in parentheses refer to comparative colour numbers

as listed in the Royal Horticultural Society Colour Chart.

WHITE. (W.) (155,157,158,159.)

Includes pale cream, ivory and colours that are nearly white or cream.

YELLOW. (Y.) (2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15,16,17,18,19.)

All shades of yellow including dresden, primrose, sulphur, mimosa, straw, lemon, amber yellow, chrome yellow (light) and maize

ORANGE. (O.) (21,23,24,25,28.)

All shades of orange including saffron, cadmium, apricot, tangerine and Indian orange.

FLAME. (Fl.) (30,31,32,33.)

Includes spectral blends, xanthic in origin, of scarlet red or orange with yellow including saturn red, mars orange, nasturtium, fire red and poppy red.

BRONZE. (Br.) (20,22,26,161,162,163,164,165,166,167,168,169,170,


Includes buff, yellow ochre, majolica yellow, spanish orange, ochraceous orange, tan, zinc orange, terracotta, burnt orange, cinnamon and greyed suffusions and blends of such tones with pink and lavender.

RED OR DARK RED (R.) (34,40,41,42,43,44,45,46,47,50,52,53,183,


Includes all shades of red from mandarin red to scarlet and crimson and also is to include cherry, claret rose, currant red, vermilion, carmine, cardinal, ox blood, and chrysanthemum crimson.

LIGHT PINK OR DARK PINK (Pk.) (27,29,36,37,38,49,51,54,55,56,62.)

Includes pale tints of orange-red and scarlets including salmon, peach, orient pink, shell pink, azalea pink, coral pink, venetian pink, french rose, porcelain rose, delft rose, empire rose, and tints and pinks of bluish tones including carmine rose, camellia rose, dawn pink, neyron rose, tyrian rose pink, china rose, phlox pink, spinel pink, rose pink, rhodamine pink and fuchsine pink.

LILAC, LAVENDER OR MAUVE. (L.) (65,68,69,73,75,76,85,91,92.)

Includes all light tints of magenta, purple and violet and to include mauve, heliotrope, lilac and lavender.

PURPLES, WINES OR VIOLETS. (Pu.) (57,58,59,60,61,63,64,66,67,70,

71,72,74,77,78,79 ,80,81,82,83,84,86,87,88.)

Includes solferino purple, indian lake, magenta, magenta rose, ruby red, garnet lake, purple madder, paeony purple, dianthus purple, beetroot purple, maroon, petunia purple, imperial purple, royal purple, amethyst violet and violet.

BLENDS. (Bls.) Varieties in which two or more colours are intermingled and gradually merge into each other and are not provided for above.

BICOLOURED. (Bic.) Varieties in which the ground colour is tipped with another colour.

VARIEGATED. (Var.) Varieties in which the ground colour is striped or splashed with another colour.

MIXED. (Mix.)  Varieties in which two or more colours are randomly arranged throughout the bloom.




Certain Groups have been sub-divided for classification and these,

with their relative sizes, are as follows:


A Giant-flowered usually over 250mm (l0in.) in diameter.

B Large-flowered usually between 200mm (8in.) and 250mm (l0in.) in diameter.

C Medium-flowered usually between 150mm (6in.) and 200mm(8in.) in diameter.

D Small-flowered usually between 100mm (4in.) and 150mm (6in.) in diameter.

E Miniature-flowered not usually exceeding 100mm (4in.) in diameter.


A Small Ball dahlias usually between 100mm (4in.) and 150mm (6in.) in diameter.

B Miniature Ball dahlias usually between 50mm (2in.) and 100mm (4in.) in diameter.


A Large Pompon dahlias usually over 50mm (2in.) and not exceeding 75mm (3in.) in diameter.

B Pompon dahlias Usually not exceeding 50mm (2in.) in diameter.


The use of "Syn" after a variety or cultivar name indicates a synonym, which may be either a horticultural synonym or one where blooms are considered indistinguishable from each other.


Last Updated 25/11/2017

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