The phrase ‘types of Dahlia’ are where these wonderful flowers are divided into groups, placing similar Dahlia varieties together. For our purposes, we’ll ignore the cellular level of distinguishing them. Instead, we’ll concentrate how Dahlias are grouped together according to their shape and size of blooms. This is meant to be a useful quick guide if you’re thinking about growing and showing your Dahlias. But it is mainly a helpful means by which us lesser mortals can choose which style of Dahlia flowers most appeal to us. (see links at the end for further tips on growing and showing)
For example, do you find yourself drawn to showy, dinnerplate sized Dahlia blooms in bright colours? Or the ‘Bishop’ series with dark foliage and ecclesiastical names? Perhaps the more unusual shaped flowers attract you? And isn’t it fun to occasionally show off your knowledge to others and blithely comment to visitors admiring your late summer border display that you prefer pompom to fimbriated types? It can also make bulb purchasing easier as the groups are often referred to in bulb catalogues.
Whether you have a thirst for knowledge, would like to show Dahlias or are simply curious as to how many types there are, I have compiled a brief compendium for you. Read on, and of course, there are pictures to make the descriptions clearer!
RHS System of Classification for the Different Types of Dahlia
These Dahlia divisions are the British ones, as per the Royal Horticultural Society and the Dahlia Society of Great Britain (established 1881). There is a RHS International agreement on classification, so other countries should only show small differences.
And, yes, the botanical Latin for Dahlia is the same as the common name. Makes life easy for once!
There are fifteen groups, or categories, of Dahlia. The majority of the familiar cultivars and garden hybrids belong in groups 1 – 9 and 11 – 15. Division 10 includes the species Dahlias and other types. And if you’re wondering why the Miscellaneous group is not at the end, it’s because new types of flower were developed and so they were added in as subsequent, new classes rather than re-numbering everything.
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
Flower sizes and flower colour classification
For general interest and because, for showing, the size of some blooms is important, an explanation of these follows at the end of the descriptions.
Different Types of Dahlia – the Official Classification
Group 1Single-flowered Dahlias
These have blooms with 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
There’s interesting detailing on these flowers. They 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
Graceful flowers with 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. The pic is helpful in showing this.
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. Some ball Dahlias may be initially mistaken for Decoratives until you look more closely.
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. These are one of my favourite types.
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. One of my favourite types.
Group 12 Star Dahlias
You’d probably look at these in the border and not realise they’re a Dahlia! But looking more closely at the flower shape gives us the clues we need. 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. A recent addition to my favourite Dahlias list, (especially the black one).
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 (another description that benefits from a pic).
Dahlia Colours and Flower Sizes
Colour division of Dahlias
Whilst the types of dahlia are classified by their flower shape and size, we also choose which ones to grow in our garden by colour. So I thought it might be of interest to quickly tell you how that is classified too, especially as many bulb catalogues use these to describe Dahlia tubers!
And it will be relevant if you want to exhibit dahlias, as where the class in which you’re exhibiting requires the blooms to be a particular colour, it needs to be predominantly but not exclusively that colour. The exception is where separate classes for bicoloured or blended blooms are included in the show schedule. General flower shows do not normally have colour classes.
Dahlia cultivars are divided into the following flower colours
- bronze
- flame
- lilac, lavender, mauve
- orange
- pink
- purple, wine, violet
- red, dark red
- white
- yellow
Blended coloured flowers are where two or more colours are intermingled and gradually merge into each other.
Bicoloured and variegated flowers are where the main colour is tipped, striped or splashed with another colour.
The RHS has a colour chart where flower colours are referred to by various numbers, but this isnt a ‘need to know’ for most of us.
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
Four facts and where to find out more about Dahlias!
There are currently more than 1700 cultivars from 22 different species of Dahlia within the National Plant Collection which is in Cornwall.
Now that’s impressive, but did you know that worldwide there are over 65,000 different Dahlia hybrids and cultivars?
Deer, rabbits, squirrels, foxes and rodents tend not eat Dahlias if there are tastier options around (such as my red orache that I forgot to net…) As with many plants, it depends on the time of year, what alternative food sources there are outside your garden and how large the local deer population is. The buds and young leaves are at more risk of being eaten than the older, tougher foliage.
As well as the National Dahlia Society, UK there are other national societies recognised internationally. These include –
The Dahlia Society of Australia, founded 1964
National Dahlia Society of New Zealand, founded 1938
The American Dahlia Society, founded 1915
Dahlia Society of France, part of founded
Plus Dahlia World – a globally recognised website resource (referenced by the above societies on their websites) It has just about everything you might want or need to know about Dahlias.
I’ve not included the web links as that can lead to issues depending on your firewall, but a quick copy & paste will get you there. But do have a look at the Plews blogs below first!
And finally
Hopefully, I’ve inspired you to grow all the different types of dahlia you may have growing in your garden or be coveting from someone else’s garden! And you may like to think about exhibiting dahlias at your local flower show. This can be great fun and you’ll find the garden club members helpful and supportive of newcomers.
Of course if you’d like some personal help with a planting design for a mixed ornamental border of bulbs, herbaceous perennials and shrubs filled with colour and bees year round, then do please get in touch to ask about our design and consultancy services.
For further gardening advice and inspiration, check out Plews Potting Shed blogs, including the selection below and you could come and find us Instagram Pinterest and Facebook for regular tips and ideas.
If you’d prefer hands-on personal help from yours truly to learn more about your garden and gardening, why not ask about our bespoke Gardening Lessons, where your classroom is actually your own garden. We can help you learn gardening basics, and also show you how to plan an ornamental border or kitchen garden. Have a read through this pdf download for info. (It’s very popular for a practical, long-lasting birthday present!)
Feeling nosey? You can have a peek at the progress of my garden renovation, Spitfires and Slow Worms, on Instagram and Facebook
You’ll get to see it in person if you come to the Plews Gardening Workshops Current ones on Eventbrite for you to book into. Follow for updates on topics and dates on Plews website, Instagram, Eventbrite, Facebook
Plus get your local garden club, allotment, WI, U3A or other group to ask me along to give a talk (and bring plants 😉)
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