The dahlia, a rather unexpected history

Dahlias have never featured in my garden. I would not say I dislike them, but I am not exactly a fan. Maybe they are just a little too showy. Many years ago, when I was a reporter walking for our local newspaper, I would cover the fiercely competitive annual dahlia show and interview the top contenders. They were devoted to their craft and so passionate about their hobby and would go into endless detail about the alchemy of soil, their favourite compost mix and breeding techniques, and of course the tragic consequences of some meteorological event. I always wondered if they, like people who see themselves as chefs, were leaving out some crucial detail when so generously sharing all their trade secrets. Or were they just confident that mere mortals would never match their dedication. Even as an avid gardener, I was never tempted to grow dahlias. Until recently.

It all started when a friend proposed an outing to buy flowers from a dahlia grower ‘on the other side of the mountain’. I am never one to say no to a road trip. Well, if roses are the prima donnas of the flower world, dahlias are surely the divas. What a display. Thousands of blooms, tunnels full of flowers. The variety was absolutely astonishing. Still not a fan of the showy double flowers, but completely smitten by single dahlias. Yes, I definitely wanted some of those.

At home, I decided I needed a list of all the single varieties, with pictures, so that I could or a few. And that was when I fell down the rabbit hole. Yes, for someone who loves historical research, I was the proverbial sitting duck. It took me two days to recall why I was interested in the dahlia in the first place.

Here is my first snippet of trivial information: the dahlia is the national flower of Mexico—and has been ever since 13 May 1963. That came as a surprise, because I had somehow placed the origin of the dahlia in Asia.

Where the dahlias bloom

Wild dahlias are generally single flowers and grow at an altitude of between 1,500 and 3,700 m are are endemic to central America, from Mexico all the way to Costa Rica. The Aztec name for dahlias was cocoxochitl or acocotle. Two manuscripts emerge from this early plant-breeding history, although both manuscripts focus on the medicinal properties of dahlia tubers—an occasional cure for colic and colds.

The earliest known record of the dahlia can be found in The Badianus Manuscript, An Aztec Herbal (1552). The manuscript was first written in Nahuatl by Martinus de la Cruz and translated into Latin by Johannes Badianus. De la Cruz and Badianus, despite their Spanish names, were Aztecs and were educated at the College of Santa Cruz (Mexico), in 1536. The Badianus Manuscript disappeared from sight and was only rediscovered in the Vatican Library in 1931.

The next character to emerge in the dahlia saga is Francisco Hernandez, personal physician to King Phillip II of Spain. Hernandez sailed for New Spain in 1570 under the King’s orders to document the natural history of Spain’s new territory. He returned in 1577 with more than 16 folios of notes and drawings, in which he also documented three different dahlias, including a semi-double form. However, Hernandez died in 1578 without ever publishing his work. Hernandez’s Thesaurus was eventually published in Rome in 1651. Interest in the dahlia’s medicinal properties waned and eventually disappeared.

The dahlia arrives in Europe

It took another hundred years before the dahlia was rediscovered as a cut flower. The dahlia was probably re-introduced into Europe in about 1788 or 1789 when Vicente Cervantes of the Mexican Botanic Garden sent a consignment to Antonia José Cavanilles, a senior botanist at the Royal Botanic Gardens in Madrid. Cavanilles raised dahlias from seed and named the genus after Andreas Dahl, a Swedish botanist who had died in 1789. Cavanilles published six books based on his work at the Royal Botanic Gardens. In his first volume (1791) he described Dahlia pinnata, and in a later volume, D. rosea and D. cocinea.

In the late 18th century there was an enormous interest in new plant species arriving from the New World. Botanists and collectors from all over Europe would have corresponded regularly with Cavanilles to exchange plant material. Cavanilles sent dahlia seeds to fellow botanists all over Europe, England, Scandinavia and Russia. This was the Age of Enlightenment, the Age of Discovery, in which soldiers, missionaries and amateur collectors sent vast quantities of exotic specimens to Europe.

Dahlia ‘fever’ and the art of hybridisation

Collectors soon discovered they could hybridise the dahlia if they bred plants from seed. In the early 1800s there was intense competition to produce a double flower. The honour eventually went to Hartwig of Karlsruhe (1808). Donckelaar, the director of the Botanic Garden in Louvain, Belgium, countered this claim with three double varieties. Next, the competition shifted to breeding rarer colours. Hammersmith Nurseries in England produced the first double purple dahlia in 1816.

Plant breeders and hobbyists produced an extraordinary number of varieties during the first half of the 19th century. Arentz of Leyden in the Netherlands had produced 72 varieties by 1819 and a double white dahlia in 1821. This double white was sold commercially as ‘Waverley’ by AC Eden & Son of Harlem (Netherlands). By 1820, Donckelaar of Belgium had produced 50 double varieties. In 1841, a plant trader in England advertised that he could offer clients more than 1,200 varieties. The first cactus and semi-cactus dahlias were produced in the Netherlands from a tuber collected in Mexico in 1872. The first waterlily dahlia was grown in New Jersey in the United States in 1893.

Today there are more than 50,000 listed varieties and the colours range from white, yellow, orange, pink, red, lavender, purple and even black, as well as variegated and bicolour varieties. Dahlias are broadly grouped according to their flowers (single, anemone, peony, pompom, decorative, etc.) and then by the diameter of their blooms (giant, large, miniature, etc.).

It is clearly a daunting catalogue to choose from, but for me, the most evocative of all the blooms must surely be the wild dahlia that supposedly grows like a weed on the high plateaux of central America.

Further reading