Dahlias are back in fashion. But horticultural whimsy says that only the smaller and less blowsy varieties are permissible. It's now absolutely okay to grow punchy little fellows such as the single-lowered, dwarf `Yellow Hammer' or the bloodshot yellow `Moonfire'. However, the flamboyantly-large types in airbrushed Walt Disney colours are still the gardening equivalent of big hair, rabbit fur and goldenesque costume jewellery. In short, they're naff.
Or so we're told by those in the know. For my part, I can't think of a single living plant - with the exception of genetically-transmogrified food crops - that doesn't stimulate me when it is well-grown and well-placed. And if I had the dedication and skill to grow eye-popping, football-sized whoppers such as the rich yellow `Bonaventure' and the blood-red `Zorro', I surely would.
Actually, it was another bloodred dahlia, the `Bishop of Llandaff' that was partially responsible for the recent reawakening of interest in this genus. Its belligerent scarlet flowers - which come popping out of shiny black-beetle buds - are soothed by elegantly-dissected dark foliage. It's an agreeable combination that ensured its desirability when it started appearing in connoisseurs' gardens in the early 1980s. And before long it became imperative for any gardener worth their salt to give pride of place in the summer border to this long-flowering, sparky dahlia.
But the Bishop had been around the block before. It arose as a chance seedling at a nursery in Cardiff in the 1920s, and it was named by its owner, Fred Treseder, after the Right Reverend Joshua Pritchard Hughes, the then incumbent at Llandaff. After winning a Royal Horticultural Society Award of Merit in 1928 it spread like a red rash all over Britain, and in 1936 The Spectator reported that it was "the most popular flower of the moment in many parts of England".
By that time dahlias had been around for yonks, swinging in and out of fashion ever since they were first introduced to Europe more than 200 years ago. Native to mountainous regions from Mexico to Colombia, they were cultivated by the Aztecs for food or animal fodder, and double-flowered hybrids were grown as garden ornamentals.
But the first record of them, in an Aztec herbal of 1582, quotes their efficacy in the treatment of urinary disorders: their Aztec name cocoxochitl translates as "water pipes". And - staying with the plumbing theme - the long stems (up to 10 metres) of the tree dahlia, D. imperialis, were used to conduct water from mountain streams and springs.
Dahlias first arrived in Europe in 1789, when Antonio Jose Cavanilles at the Madrid Botanic Garden received seed from Vicente Cervantes, a botanist at Mexico city's botanic gardens. Cavanilles named the genus after Andreas Dahl, a Swedish botanist and pupil of Linnaeus. (Incidentally, around the same time, another botanist, Willdenow, decided that Georgina was a better name. This alias still persists in Scandinavia as a popular name.)
From the time the dahlia appeared in Europe it was eagerly hybridised, and 55 new varieties had been bred by 1806. By the 1840s there were 1,500, and today there are 20,000 cultivars - all of which have arisen from the crossing and recrossing of two species and their progeny: Dahlia coccinea and D. pinnata.
Another species dahlia, D. merckii, is sometimes grown in gardens here, and its soft lavender, simple flowers lend a gentle grace to the late-summer and autumn garden. Before the present fad for dahlias, it was one of the few - along with the Bishop - that was allowed in fashion-conscious borders. Mind you, it's not easy to find, and is generally available only in the smaller, more specialised nurseries and garden centres.
On the other hand, the supermarket or chain store is not to be sneezed at when it comes to finding interesting plants. Some of the warmest, choicest dahlia blooms I've seen this year came from their shelves. So next spring and summer, keep your eyes peeled for dahlia tubers in the unlikeliest places.
And a special Irish dahlia (not available for sale) exists at Glenveagh in Donegal. Dozens of `Matt Armour' are massed in beds in the walled garden, giving a dazzling display of single red flowers (similar to the species D. coccinea) from July until first frost. At Glenveagh the tubers are dug up every year, stored and replanted the following year.
In warmer parts of the country dahlias are hardy, and only the most committed of gardeners (including the football-growers) dig up and store the tubers. Chief among pests are slugs and earwigs. Protect your dahlias from these little monsters, grow them in sunny, well-drained and rich soil, feed them weekly, deadhead them zealously and you will be entertained by insanely cheerful blooms for months on end.
Diary date: Today, 2.306 p.m. and tomorrow, 26 p.m. Naul Gardening Club, 10th anniversary show, Naul, Co Dublin. See the amazing blooms grown by some of the country's top dahlia exhibitors, including Frank Hoey, the Irish Dahlia Champion from Drogheda. Admission: £1.