Different Types of Dahlia
This is your quick guide to the Dahlia Classification Groups which you’ll need for showing and exhibiting your beautiful blooms at a flower show, whether that’s a Biggin Hill Horticultural Society Show or another local gardening club or village show..
Like most local flower shows, we follow the National Dahlia Society (NGS) 2015 classification as does the RHS. However, we do not classify types of dahlia by colour. (Which keeps it simple when the majority of us are amateur growers)
Parts of a Dahlia flower
The essential names of parts to remember when working out which group a Dahlia should be in!
Florets – term used for petals, ray florets are the outer petals, disc florets the inner petals
Involute – petals edges curved or rolling inwards, giving a saucer shaped appearance
Revolute – petal edges curved or rolling outwards
Dahlia flower sizes
For show purposes, some groups are subdivided by size as follows. Always check the show schedule, as general flower shows may vary from specific Dahlia shows. If the Group number isnt mentioned below, then the bloom size is irrelevant, unless mentioned in the show schedule.
Groups 4, 5, 8, 9 & 11
Giant: more than 250 mm diameter
Large: 200 – 250 mm diameter
Medium: 150 – 200 mm diameter
Small: 100 -150 mm diameter
Miniature: not more than 100 mm diameter
Group 6
Small ball: 100 -150 mm diameter
Miniature Ball: 50 -100 mm diameter
Group 7
Large Pompom: 50 -75 mm diameter
Pompom: not more than 55 mm diameter
Different Types of Dahlia – the Official Classification
Group 1 Single-flowered Dahlias
The blooms have a single outer ring of florets, which may overlap; the centre forms a disc. The ‘original’ Dahlias were single flowered.
Group 2 Anemone-flowered Dahlias
These beauties have one or more outer rings of usually flattened ray florets, surrounding a dense group of tubular disc florets.
Group 3 Collarette Dahlias
These have a single outer ring of overlapping florets, with a ring of small florets, called the collar, forming a disc in the centre.
Group 4 Waterlily Dahlias
Fully double blooms. Broad petals are slightly involute along their full length. The bloom depth should not be more than 1/3 of the diameter
Group 5 Decorative Dahlias
Perhaps a flower shape we most of us easily recognise as a Dahlia, these have fully double blooms showing no disc. The ray florets are generally broad & flat may be involute or slightly twisted for no more than 75% of their length
Group 6 Ball Dahlias
Fully double blooms, they are usually ball shaped but can also be slightly flattened. Ray florets are rounded at the tips, and the margins are spirally arranged and involute for at least 75% of the length.
Group 7 Pompon Dahlias
As the name suggests, these Dahlias look like a pompom ball!. They have fully double spherical blooms, as with florets curved along their length.
Group 8 Cactus Dahlias
Fully double blooms, with ray florets that are usually pointed, narrow and revolute for 65% or more of their length. The ray florets may be straight or incurving.
Group 9 Semi-Cactus Dahlias
Also with fully double blooms. The ray florets are usually pointed & revolute for more than 25% but less than 65% of their length. They may be broad at the base, straight or incurving.
Group 10 Miscellaneous Dahlias
Any Dahlias which do not fall into the other group types. This group includes species Dahlias.
Group 11 Fimbriated Dahlias
These blooms are sometimes called fringed Dahlias – for obvious reasons! The tips of the ray florets should be evenly split or notched into two (or more). The notching should be uniform throughout the bloom to create an overall fringed effect.
Group 12 Star Dahlias
You’d probably look at these in the border and not realise they’re a Dahlia! The blooms have a single outer ring of florets surrounding the disc. The ray florets are uniformly either involute or revolute and so curled that on first glance they seem narrow.
Group 13 Double Orchid Dahlias
Double Orchid Dahlias have fully double blooms showing no disc and have triangular centres. The ray florets are narrowly lance shaped and either involute or revolute.
Group 14 Paeony Dahlias
Paeony Dahlias have multiple outer rings of ray florets surrounding a disc. These ray florets are flat or slightly involute at base, and are then flat or slightly revolute fo the rest of their length.
Group 15 Stellar Dahlias
Fully double blooms showing no disc. Ray florets are long & narrow along their length preferably with pointed tips. They should show a uniform arrangement with spaces between the partially involute florets in each of the rows, and also displaying a “U” shaped cross section for most of their length. The bloom depth should be more than half but not greater than diameter.
Different Types of Dahlia –Don’t Panic!
There are many different types of Dahlia, and although it all looks technical, once you compare the pictures and descriptions to the flowers in your garden it all begins to fall into place.
And hopefully, you now have the information you need to know what they are. Happy growing and showing!
