Classification of dahlia varieties is a fluid subject. Botanists argue about the division of species and growers create increasing numbers of cultivars and varieties. Thus, the dahlia landscape is both complex and continually changing.
Dahlia varieties grouped by flower characteristics
Some order is imposed on this complexity by the arrangement of different dahlia varieties into groups, classified according to the characteristics of their flowers.
Even this grouping system is not straightforward, as there can be sub-divisions within the groupings and International approaches can differ somewhat.
For these purposes, I’ll focus on the approach of the UK’s National Dahlia Society (NDS). According to the NDS, there are currently 15 groups of dahlias. The different groups are set out below, but in order to understand the differences between the various groupings, it is useful first to understand something about the parts of dahlia flowers.
Dahlia is a genus within the Asteraceae family, whose members also include daisies, sunflowers, rudbeckia and the like. Asteraceae plants typically have a flower head, or capitulum, that is a composite of a number of smaller individual flowers. This explains why the Asteraceae family was formerly known as Compositaea.
The individual dahlia flowers are called ‘florets’ and there are two different kinds. At the centre of the flower are the ‘disc florets’, which are typically yellow. The reproductive parts of the disc florets are usually readily accessible to pollinators, so this is where we see bees collecting pollen from.
The other kind of floret is the ‘ray floret’. Ray florets are what we usually think of as petals. These are the showy, coloured structures which surround the disc florets on the outer portion of the capitulum.
In dahlias, ray florets are sterile, so no reproductive parts (stamens or pistils) are evident. Ray florets will vary in their characteristics – they may be flat, folding up at the edges (involute) or folding down at the edges (revolute). Dahlia pinnata, for example, has a simple arrangement of flat ray florets.
Smaller Dahlia varieties – size classifications
Smaller Dahlias are also often classified by size, usually for exhibition purposes. The classifications are as follows (the abbreviations noted are used below in relation to the cultivars listed):
- Dwarf bedding dahlias (DW.B) – plants grow up to 60cm (24 in) in height.
- Lilliput dahlias (Lil) – plants plants grow up to 30cm (12 in) in height, flowers up to 7.5cm (3 in) in diameter.
- Gallery Dahlias – plants plants grow up to30cim (12 in) in height, with flowers larger than Lilliput dahlias.
Details of all 14 Dahlia groups are below:
These dahlias have flowers with a single ring of flat ray florets, which often overlap. Contrasting colour often appears towards the centre. The disc florets form a central disc.
Suggested Single Flowered Dahlia cultivars for garden use are:
Chessy (Lil) (Yellow)
Magenta Star (Lilac)
Hadrian’s Sunset (Orange)
HS Romeo (Red)
HS Princess (White)
Niki Preston (Orange/Pink)
Anemone flowered dahlias have blooms with one or more outer rings of flat ray florets, which are usually flat, with central display of tubular florets. No disc is visible.
Suggested Anemone Flowered Dahlia cultivars for garden use are:
Alpen Fury (Red/Yellow)
Pasa Doble (White/Yellow)
Ryecroft Jim (Pink/Yellow)
Collerette dahlias have an outer ring of 8 or more flat overlapping ray florets, with an inner ring of smaller, symmetrical ray florets (the Collar), which are often of a different colour. The centre forms a disc.
Suggested Collerette Dahlia cultivars for garden use are:
Bride’s Bouquet (White)
Christmas Carol (Red/Yellow)
Clair de Lune (Yellow)
Linda C (Pink)
Kirsty G (Red)
Waterlily dahlias have fully double blooms with broad, somewhat sparse ray florets that can be straight or slightly involute along their length. This gives the flower a shallow appearance. The centre of the flower should be firm and closed and the depth of the flower overall should be around one third of the diameter of the bloom. (Image copyright FD Richards)
Suggested Collerette Dahlia cultivars for garden use are:
Anna Lindh (White)
Shep’s Memory (Bronze)
Wildwood Marie (Pink)
Kate’s Dream (Red)
Creme de Cassis (Lilac/Purple)
The essence of decorative dahlias is that they have fully double blooms, with no disc showing. The ray florets are generally flat, broad and are often involute for most of their length. The florets may be slightly twisted and usually bluntly pointed. Many modern varieties have a high petal count.
Blooms sizes are:
Giant flowered decoratives – over 25 cm (10 inches) in diameter
Large flowered decoratives – 20 – 25 cm (8-10 inches) in diameter
Medium flowered decoratives – 15 – 20 cm (6-8 inches) in diameter
Small flowered decoratives – 10 – 15 cm (4-6 inches) in diameter
Miniature flowered decoratives – Up to 10 (4 inches) in diameter.
Suggested Formal Decorative Dahlia cultivars for garden use are:
Hamari Gold (Giant Flower) (Pink)
White Perfection (Giant Flower) (White)
Lavender Perfection (Giant Flower) (White)
Cafe au Lait (Large Flower) (White/Bronze)
Ryecroft Rebel (Large Flower) (White/Pink)
Berwick Wood (Medium Flower) (Purple)
Mary Margaret Row (Medium Flower) (Yellow)
Oreti Classic (Medium Flower) (Lilac)
Barbarry Sultan (Small Flower) (Red)
Edinburg (Small Flower) (Purple/White)
Hillcrest Firecrest (Small Flower) (Yellow/Orange/Red)
Requiem (Small Flower) (Purple)
Andrea Lawson (Miniature Flower) (White/Lilac)
Barbarry Respectable (Miniature Flower) (Pink)
Gallery Singer (Gall) (Miniature Flower) (Red)
Ball dahlias are similar to decorative dahlias in that they have fully double blooms, which are ball shaped (obviously) or slightly flattened. The ray florets follow a spiral form and are tubular, rounded at the tips and involute for most of their length.
Suggested Ball Dahlia cultivars for garden use are:
Amy Cave (Small Ball) (White)
Marble Ball (Small Ball) (Purple/White)
Regal Boy (Small Ball) (Purple)
Aurora’s Kiss (Miniature Ball) (Red)
Downham Royal (Miniature Ball) (Purple)
Ruskin Tangerine (Miniature Ball) (Orange)
Pompon dahlias are globular double blooms with tubular ray florets which are blunted at the tips. They are usually less that 5cm (2 inches) in diameter and popular in gardens or for cut flowers. Large Pompons have blooms between 5 and 7.5 cm (2-3 inches).
Suggested Pompon Dahlia cultivars for garden use are:
Amgard Beacon (Large Pompon) (Yellow)
Franz Kafka (Large Pompon) (Purple)
Ms Kennedy (Large Pompon) (Orange)
Bowen (Pompon) (White)
Pensford Marion ( Pompon) (Pink)
Martin’s Yellow (Pompon) (Yellow)
Johann (Pompon) (Red)
(Image: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=46202)
Cactus dahlias have fully double blooms with pointed and narrow ray florets that are revolute for more than half of their length. Sometimes the florets curve inwards.
Blooms sizes are:
Giant flowered cactus dahlia – over 25 cm (10 inches) in diameter
Large flowered cactus dahlia – 20 – 25 cm (8-10 inches) in diameter
Medium flowered cactus dahlia – 15 – 20 cm (6-8 inches) in diameter
Small flowered cactus dahlia – 10 – 15 cm (4-6 inches) in diameter
Miniature flowered cactus dahlia – Up to 10 (4 inches) in diameter.
Suggested Cactus Dahlia cultivars for garden use are:
Good Earth (Medium Cactus) (Pink/White)
Sure Thing (Medium Cactus) (Red)
Clearview Sharron (Medium Cactus) (Yellow)
Deborah’s Kiwi (Small Cactus) (Pink/White)
Karras 150 (Small Cactus) (White)
Embrace (Small Cactus) (Orange)
Gracie S (Miniature Cactus) (Purple)
Weston Pirate (Miniature Cactus) (Red)
Tui Avis (Miniature Cactus) (Pink)
Semi-Cactus dahlias have fully double blooms, but differ from true Cactus dahlias in that they have broader ray florets that are only revolute for about half their length. The florets may be broad at the base can be straight curve upwards. (Image:By I, ritchie66.eu, CC BY-SA 3.0, Link)
Blooms sizes are:
Giant flowered semi-cactus dahlia – over 25 cm (10 inches) in diameter
Large flowered semi-cactus dahlia – 20 – 25 cm (8-10 inches) in diameter
Medium flowered semi-cactus dahlia – 15 – 20 cm (6-8 inches) in diameter
Small flowered semi-cactus dahlia – 10 – 15 cm (4-6 inches) in diameter
Miniature flowered semi-cactus dahlia – Up to 10 (4 inches) in diameter.
Suggested Semi-Cactus Dahlia cultivars for garden use are:
Aitara Majesty (Giant Semi-Cactus) (Yellow)
Inca Dambuster (Giant Semi-Cactus) (Yellow)
Candy Keene (Large Semi-Cactus) (Pink/White)
Black Jack (Large Semi-Cactus) (Red)
Aloha (Medium Semi-Cactus) (Yellow/Red)
Cleo Laine (Medium Semi-Cactus) (Orange/Pink)
Nancy Margaret (Medium Semi-Cactus) (White)
Veritable (Medium Semi-Cactus) (Lilac/White)
Avoca Comanche (Small Semi-Cactus) (Orange)
Match (Small Semi-Cactus) (Purple/White)
Ruskin Andrea (Small Semi-Cactus) (Pink)
Shandy (Small Semi-Cactus) (Orange/Pink)
Badger Twinkle (Miniature Semi-Cactus) (White/Purple)
Weston Dusky (Miniature Semi-Cactus) (Red)
Weston Stardust (Miniature Semi-Cactus) (Pink/Yellow)
This group includes those that do not come within Groups 1 – 9 inclusive and Groups 11, 12,13 & 14. Species dahlias fall within this group. (Image: OPDBLP (Acervo fotográfico del OPD Bosque La Primavera) / CC BY-SA)
Suggested Miscellaneous Group Dahlia cultivars for garden use are:
Dahlia coccinea (Species) (Red)
Dahlia pinnata (Species) (Red)
Jewel Orange (Dw.B) (Purple)
Samantha (Lil.) (Pink)
Lorona Dawn (Purple/White)
On Fimbriated dahlias, the tips of the ray florets have two or three even splits or notches, creating a ruffled or fringed effect. The florets themselves can vary and may be flat, involute, revolute, straight, incurving or twisted.
Suggested Fimbriated Dahlia cultivars for garden use are:
Jean Ellen (Yellow)
Kenora Frills (Pink/White)
Mel’s Orange Marmalade (Orange)
Marlene Joy (White/Pink)
Star dahlias have a single outer ring of ray florets around the central disc, which are either all involute or all revolute.
Suggested Star Dahlia cultivars for garden use are:
Hillcrest Cheryl (White)
Honka Surprise (Pink)
Midnight Star (Dark Red)
Sophie Taylor (Orange/Yellow)
Veronne’s Obsidian (Purple)
(Image by Marktee1 at en.wikipedia, CC BY-SA 3.0, Link)
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.
Suggested Double Orchid Dahlia cultivars for garden use are:
Gallery Art Deco (Gall) (Orange)
Gallery Art Nouveau (Gall) (Pink/Purple)
Jescot Julie (Orange/Purple)
Paeony flower dahlias have several rings of ray florets encircling a central disc. The ray florets are often revolute along their length but slightly involute at the bases.
Suggested Paeony Dahlia cultivars for garden use are:
Bishop of Llandaf (pictured)
Bishop of Auckland (Dark Red)
Bishop of Canterbury (Purple)
Bishop of Leicester (White/Pink)
Bishop of York (Yellow)
Classic Rosamunde (PinkD
Stellar dahlias have double blooms with no disc and long, narrow and pointy ray florets, that are partially involute (u-shaped). The florets recurve (turn back) towards the stem.
Suggested Stellar Dahlia cultivars for garden use are:
Alloway Candy (Pink/White)
Camano Pet (Yellow/Orange).