Hot-coloured dahlias look especially well in the glowing, lower light at this end of the gardening year, writes Jane Powers
Some flowers put me in a very, very good mood. Dahlias, for instance: how could anyone be grumpy around their cartoony, psychedelic blooms? They come in every colour along the spectrum except blue (but breeders are working on that) - red, orange, bronze, yellow, purple and pink - in all degrees of saturation and in all manner of combinations. There are white dahlias and near-black ones (one of the darkest that is not too difficult to find is the deep-maroon 'Arabian Night', bred more than 50 years ago in The Netherlands). And their structure may be anything from a neat pompom, smaller than a ping-pong ball, to a giant and effusive mass of petals larger than a human head.
They are one of the earliest plants known to have been cultivated, and are mentioned in an Aztec herbal of 1582, which recommends them for the treatment of urinary disorders. One of the Aztec names for the plant is cocoxochitl, which means water pipes. In more modern times the roots, which contain inulin, have been used to make a sugar substitute suitable for diabetics.
My favourite abstruse fact about dahlias concerns William A Mitchell, a Minnesota-born chemist, who died in 2004. He was the man who invented those iconic, all-American sugary products Jell-O, Cool Whip, Tang and Pop Rocks. Dahlia buffs will be interested to know that he also invented the not-quite-so-famous Dacopa, a coffee substitute made from the roasted tubers of the plant.
So the gaudy-flowered dahlia isn't just a plant with a pretty face. Or, rather, make that 20,000 faces, for that is the number of cultivars listed in the International Register of Dahlia Names, managed by the Royal Horticultural Society. Amazingly, all have their origins in two wild species from Mexico and Guatemala, D. coccinea and D. pinnata, whose progeny have been crossed, re-crossed and back-crossed ad infinitum.
Dahlias were tremendously popular among European and American gardeners from the middle of the 19th century onwards, both as hobby plants and as border specimens. Victorians used them to hide the gangly legs of their hollyhocks. In 1936 the Spectator reported that the blood-red-flowered and dusky-foliaged 'Bishop of Llandaff' was "the most popular flower of the moment in many parts of England".
Yet, 20 or 30 years later, people who considered themselves to be paragons of taste in matters horticultural wouldn't let a dahlia through the garden gate. In just a few decades they had gone from being objects of desire to indications of vulgarity.
But how fickle fashion is. After a shaky reappearance about 15 years ago, encouraged in part by the late Christopher Lloyd at Great Dixter, the dahlia is once again strutting its stuff in all the "best" borders. For a while only the 'Bishop of Llandaff' was readmitted, but in the past few years dahlias of all colours, shapes and sizes have got their feet in the door.
For late-summer and early-autumn joviality they cannot be beaten. The hot-coloured kinds look especially well in the more glowing, lower light at this end of the gardening year. 'David Howard', with its gorgeous apricot petals, and a deeper red-bronze centre, is the perfect partner for buff-coloured grasses and the tall and airy, purple-bobbled Verbena bonariensis. The famous 'Bishop of Llandaff' has sired a number of offspring, all with the same dark foliage as their parent. So now we have Bishops of Canterbury (wine-purple petals), Auckland (pinky-crimson), Lancaster (red, double), Leicester (light lavender), Oxford (copper-orange) and York (gold). They're not that easy to find as plants, but if you're willing to accept a mixed bag of ecclesiastical spawn, you can try 'Bishop's Children', available as seed from Mr Fothergill's and Thompson & Morgan.
Warm-toned dahlias combine well with large-leaved or tropical-looking plants such as bananas, cannas, Melianthus major and castor oil plant (Ricinus communis) and trees such as Paulownia and Eucalyptus gunnii, which are pollarded (cut back dramatically in spring) and grown as foliage specimens. They also shine out against grey-leaved plants such as Artemisia.
If you're growing dahlias as part of a border scheme, choose varieties with good stiff stems. Besides those that we've mentioned already are 'Roxy' (neon purple flowers), 'Hillcrest Royal' (spiny purple-pink) and 'Murdoch' (lipstick red). But, really, there are too many to name here, and availability can be patchy. But now is a good time to buy, as they're in flower, and you can see who's standing proud and upright, and who's a slumper and in need of support. jpowers@irish-times.ie
HOW JOHN GRACE GROWS DAHLIAS
Dahlias can also be grown in great single-genus crowds, with no other plants to distract from their wonderfully unrestrained blooms. This is the preferred method of some collectors, such as John Grace (below) of Charlefield Farmhouse in the Rower, Co Kilkenny. He grows 300 varieties (a man can never have too many dahlias) in long rows on a
rectangular piece of land. There they act as a magnet for butterflies, which flit and dither among the mad-coloured flowers.
Dahlias prefer an open, sunny position - which is exactly what they get behind the 18th-century farmhouse - and a good rich soil with plenty of moisture. (If yours is dry ground, incorporate lots of organic material and keep the surface mulched, to conserve water.) In colder parts of the country the tubers must be lifted every year, as they may be destroyed by frost. Grace digs his up (yes, all 300 of them) about a week after the first frost, and cuts back the stems to a few inches. Then - here's the clever bit - he stands the tubers upside down, with the truncated stems acting as short legs, and lets them dry off in a frost-free place. After six weeks he packs them in peat moss.
January and February find Grace digging the ground and adding lots of farmyard manure. The tubers are planted again in early April and given some sulphate of potash a month later. The first blooms appear in early July, and they continue (deadheading is essential) until frost cuts them down around the end of October. Wind can flatten a dahlia plantation, but here the rows are sensibly girdled with an arrangement of stakes and baling twine.
Caterpillars may be a nuisance, but slugs and snails - which can destroy a plant overnight, especially when it emerges in spring - are not a significant pest here. And thank goodness for that, because this Technicolor host of Kilkenny dahlias has been one of the more uplifting sights of my summer.
Winchester Growers, in Cornwall, holds a national collection of dahlias under the auspices of the National Council for the Conservation of Plants and Gardens (NCCPG, a UK and Ireland organisation): see www.dahlias.ukgardeners.com and www.wgltd.co.uk
DIARY DATES
Some of the finest show dahlias in Ireland (as well as numerous other flowers and kinds of garden produce) can be seen at Naul and District Gardening Club's annual show today (3-6pm) and tomorrow (2-6pm), at Clann Mhuire GAA Grounds, Naul, Co Dublin. Admission €3