Dahlias 1

What else could I write about this week besides for dahlias?! I love opening the curtains in the morning to be greeted by the most stunning display of these breath taking flowers during August and September.

A little bit of Dahlia history

Impress your friends with some little known dahlia facts:

  • The dahlia is named in commemoration of the Swedish botanist Andreas Dahl who was a pupil of the famed botanist Carl Linnaeus.
  • The name was not given by Linnaeus himself as some mistakenly presume but rather by the Spanish botanist José Cavanilles, Director of the Royal Gardens of Madrid. Who named the Dahlia in 1791 in commemoration of Andreas Dahl who had died in 1789.
  • Dahlias were first introduced into Britain in 1798 by the Marchioness of Bute, wife of The Earl of Bute, the English Ambassador to Spain, who obtained a few seeds from Cavanilles and sent them to Kew Gardens, where they flowered but were lost after two or three years.

What is a Dahlia?

The dahlia is a half-hardy tuberous-rooted perennial originating in Mexico. It is a member of the Asteraceae  dicotyledonous plants, related species include the sunflower, daisy, chrysanthemum, and zinnia. There are 42 species of dahlia, with many hybrids commonly grown as garden plants. Flower forms are variable ranging in size from as small as 5 cm in diameter up to the giant 30 cm “dinner plate” dahlias.

Choosing Dahlias – Classification

Through selective breeding there are now many different kinds of dahlia available. The RHS has catalogued over 57,000 different cultivars! These are grouped into fourteen classification based on the flower type – which is what most gardeners use to choose and identify the dahlias they want to grow and display in their gardens.

The groups are as follows (the abbreviations are those used by the RHS):


  • Group 1 – Single-flowered dahlias(Sin) — Flower has a central disc with a single outer ring of florets (which may overlap) encircling it, and which may be rounded or pointed.

  • Group 2 – Anemone-flowered dahlias(Anem) — The centre of the flower consists of dense elongated tubular florets, longer than the disc florets of Single dahlias, while the outer parts have one or more rings of flatter ray florets. Disc absent.
  • Group 3 – Collerette dahlias(Col) — Large flat florets forming a single outer ring around a central disc and which may overlap a smaller circle of florets closer to the centre, which have the appearance of a collar.
  • Group 4 – Waterlily dahlias(WL) — Double blooms, broad sparse curved, slightly curved or flat florets and very shallow in depth compared with other dahlias. Depth less than half the diameter of the bloom.
  • Group 5 – Decorative dahlias(D) — Double blooms, ray florets broad, flat, involute no more than seventy five per cent of the longitudinal axis, slightly twisted and usually bluntly pointed. No visible central disc. (The dahlia in this posts image is a decorative).
  • Group 6 – Ball dahlias(Ba)— Double blooms that are ball shaped or slightly flattened. Ray florets blunt or rounded at the tips, margins arranged spirally, involute for at least seventy five percent of the length of the florets. Larger than Pompons.
  • Group 7 – Pompon dahlias(Pom) — Double spherical miniature flowers made up entirely from florets that are curved inwards (involute) for their entire length (longitudinal axis), resembling a pompon.
  • Group 8 – Cactus dahlias(C) — Double blooms, ray florets pointed, with majority revolute (rolled) over more than fifty percent of their longitudinal axis, and straight or incurved. Narrower than Semi cactus.
  • Group 9 – Semi cactus dahlias(S–c)— Double blooms, very pointed ray florets, revolute for greater than twenty five percent and less than fifty percent of their longitudinal axis. Broad at the base and straight or incurved, almost spiky in appearance.
  • Group 10 – Miscellaneous dahlias(Misc) — not described in any other group.
  • Group 11 – Fimbriated dahlias(Fim) — ray florets evenly split or notched into two or more divisions, uniformly throughout the bloom, creating a fimbriated(fringed) effect. The petals may be flat, involute, revolute, straight, incurving or twisted.
  • Group 12 – Single Orchid (Star) dahlias(SinO) — single outer ring of florets surround a central disc. The ray florets are either involute or revolute.
  • Group 13 – Double Orchid dahlias(DblO) — Double blooms with triangular centres. The ray florets are narrowly lanceolate and are either involute or revolute. The central disc is absent.
  • Group 14 – Peony-flowered dahlias(P) — Large flowers with three or four rows of rays that are flattened and expanded and arranged irregularly. The rays surround a golden disc similar to that of Single dahlias.

In my next post I’ll write about dahlia care and propagation.



Leave a Reply

Your email address will not be published. Required fields are marked *