Dahlias: how to grow beautiful dahlia flowers
For a few years dahlias were branded garish, old-fashioned and only grown by fiercely competitive Mr McGregor types, armed with rulers, hoping to win prizes at the local flower show. Now they are firmly back in fashion, used by all the most sought-after florists from Scarlet & Violet to The Land Gardeners. Bridging the gap between summer and autumn, they provide colour and drama from August often until November. ‘The joy of dahlias is that growing them is a never- ending journey of discovery,’ says Oxfordshire flower grower Rachel Siegfried, who grows dahlias for cutting on her farm, Green & Gorgeous. ‘There are so many of them that you can try new ones each year and you will never get bored.’
Are dahlias perennials?
Dahlias are classed as tender perennials, which means that the tubers can in theory be left in the soil over winter, but in climates such as the UK they may succumb to the cold or damp. Whether to lift the tubers each autumn to overwinter them under cover is a hotly debated topic, and it largely depends on where you live and the conditions in your own garden. In the south, it is generally safe to leave the plants in the ground over winter, provided you mulch with newspaper, straw or compost to protect them. However, an extremely cold winter with periods of prolonged, intense cold, could see off all but the most tenacious plants.
If you decide to be cautious, the tubers should be dug up in late autumn after the first frost has blackened the foliage and stems, and stored in a box of compost or sand, leaving the crowns poking out at the top. In spring, these tubers can then be forced into early growth by potting them up, to be planted out in the border in late spring.
Get them out in spring ready to grow on, which is when you should divide the tubers. If you have a green-house, conservatory or spare windowsill, you can start dividing and potting them up in late March or April. If the tubers are still fairly small, they can be chopped or pulled in half and each side used to make a new plant. ‘Look for the eyes on the tubers,’ says Rachel Siegfried. ‘As long as each division has an eye, it can be used to make a new plant.’ If the clump is bigger, it can be divided using a pruning saw.
How to plant dahlia tubers
Dahlias do best in an open, sunny situation in a fertile soil that doesn't get too dry. Usually grown from tubers, dahlias should be planted after the last frosts in spring. Plant the tubers into soil prepared with plenty of well-rotted compost or manure, and water well until established. To make healthy, bushy plants with lots of flowers, pinch out all but five of the shoots sprouting from the tuber as you plant them, and as these grow, pinch out the tips too. A dose of blood, fish and bone scattered around the stem a week after planting encourages strong growth, and for extra flower power, a liquid feed high in nitrogen and potash can be given once a week in summer.
The National Dahlia Collection sell rooted cuttings, most of which will flower in their first year and also establish a tuber. If you are growing dahlias from cuttings it is recommended that you leave them in the ground for as long as possible as the majority of weight is put on tubers towards the end of the growing season. An easy way of timing this is to let your dahlias take the first frost of winter - following this, their leaves will go brown and they will look generally sorry for themselves. At this point, carefully dig them up, cut back the growing stems and then leave them to dry upside-down, so that any damp left in the stems can drain out.
How to care for dahlias
Always stake your dahlias as soon as you plant them out and then tie them in as they grow. When the plants are fully established, they will hide any unsightly sticks and won't slump over. Use strong pieces of wood, not bamboo, which is the perfect hiding place for earwigs who will snack on your tender plants. Always protect against slugs - this is particularly important in the early stages to avoid heartbreak.
As soon as you see buds developing, start feeding your dahlias. The folks at the National Dahlia Collection recommend a proprietary tomato food once every 10 days.
Deadheading dahlias
When your plants start blooming, be meticulous about deadheading. If you keep on picking the flowers, you'll have a constant supply of blooms from July to November. Before you put them in a vase, Sarah Raven recommends re-cutting the hollow stem under water to avoid airlocks.
What varieties of dahlia are best?
The reason that there are so many shapes, sizes and colours of dahlia is because they have more chromosomes than other plants. This means there is more variation in form when the plants cross-fertilise, resulting in the incredible diversity we see today. There are more than 10 categories of dahlia, grouped by flower shape, including pompon and ball dahlias, decorative, waterlily, peony, cactus, single and anemone.
‘When you’re growing dahlias as cut flowers, it’s best to go for small to medium flowers, with the odd larger one thrown in,’ says Rachel Siegfried. ‘The other crucial thing is height: you don’t want the dwarf, bedding-type dahlias because you can’t get the stem length you will need for cutting, so don’t go for a plant that’s going to be under a metre tall.’ Most dahlias can be used for cutting, but some are better than others – either because they last longer in the vase, or because they have tall and clearly defined stems. ‘If I had to choose just one type, it would be the waterlily dahlia because of the softness of it and because it just lends itself to cutting,’ says Rachel. ‘Singles, collarettes, anemones and cactus types don’t have quite as much vase life, but I still like to grow them for the variety of form.’
Rachel's particular favourites include the following;
- Waterlily ‘Carolina Wagemans’: ‘When it first opens, its flowers are apricot, with a two-tone effect and, as it ages, it becomes more pink. It has good stem length and is prolific in flower.’
- Waterlily ‘Sam Hopkins’: ‘This is the best of several dark waterlily types, with flowers of the deepest, velvety red – almost black in the centre.’
- Decorative ‘Eveline’: ‘This has white flowers with a hint of lilac in the middle and around the edges of the petals. It’s one of my top bridal flowers.’
- Cactus ‘Orfeo’: ‘This is an unbelievable colour – electric pink and almost iridescent – with large flowers. It’s a prolific flowerer and has good stem length.’
- Decorative ‘Peaches’: ‘This is a decorative, with bicoloured blooms of warm peachy-orange with white tips to the petal.’
- Large decorative ‘Cafe au Lait’: ‘I love its creamy, beige-pink flowers and wouldn’t be without it for its opulence and size.’
Dark-flowered cultivars are always popular, and recent introductions include D. 'Karma Choe', a water-lily type with dark velvety flowers suffused with crimson. D. 'Dark Desire' has elegant single flowers in deep chocolatey red with contrasting golden stamens. For something with more punch, D.'Acapulco' is a new cactus dahlia that has strawberry-red flowers with a deep pink centre, while D. 'Lorona Dawn' has distinctive, pink single flowers with a white ruffle and bright yellow centre. Another one-off is D. 'Alloway Candy', a double orchid type in pale pink tinged yellow. Also look out for D. 'Dakota', launched in 2011, with single flowers in pale orange, edged with red. This is just a handful of some of the new range available, with new varieties to look out for and try each year.
A short history of dahlias
Explosive shapes and fabulous colours make the dahlia one of the most visually arresting plants we grow, so it is surprising to find that it doesn't have the breadth of artistic history that many other plants have. This is partly because it is a relative newcomer to our gardens, arriving via Spain from Mexico at the end of the eighteenth century (although it had been widely cultivated in Mexico for hundreds of years before this). The first known illustration of the dahlia appeared in an Aztec herbal in 1552 - a simple coloured painting of Dahlia coccinea with its single red flowers - and it was around this time that the dahlia was first discovered by a European, Francisco Hernandez, physician to the King of Spain, who also illustrated several double-flowered dahlias in his own posthumously published herbal. Despite this initial flurry of interest, somehow the dahlia missed the boat - unlike other South American plants discovered by the Spanish at the same time, such as the passion flower and the tomato - and it wasn't until a good 250 years later that the plant was grown successfully in Europe.
The first dahlia species flowered in the Royal Botanic Gardens of Madrid around 1790, causing an immediate stir among the botanical fraternity of Europe. A frenzy of correspondence ensued, and the first dahlia seed was sent to Kew in 1798, but frustratingly the plants raised from this seed were promptly lost without being propagated, so the race was still on. The dahlia's introduction to Britain is widely credited to Lady Holland, a well known society figure and political hostess who sent back seed of Dahlia pinnata from the Royal Botanic Gardens in Madrid, and the first plants flowered in her garden at Holland House in 1804. But a colour painting of D. coccinea, which appeared in the same year in Curtis's Botanical Magazine, indicates that Lady Holland had been pipped to the post. The year before, in 1803, a few precious specimens of D. coccinea had flowered in the garden of John Fraser, a little-known plant hunter who ran a nursery in Sloane Square. Interest in this new, exotic plant accelerated quickly, to the point that it was described by the garden designer John Claudius Loudon in 1822 as 'the most fashionable flower in the country'. With seed of new, double varieties being thrown into the melting pot, horticulturists realised how wonderfully variable the dahlia was and soon an exciting range of different types was being developed, all of which were illustrated and pored over in botanical magazines. One of the most beautiful dahlia paintings is Pierre-Joseph Redoute's Dahlia pinnata (c. 1830), which captures the opulence and texture of the flower. But the tastefulness of this elegant painting is at odds with the subsequent development of the plant. Spurred on by an increased interest in growing dahlias for showing, breeders in the late nineteenth and early twentieth centuries got thoroughly carried away, producing increasingly outlandish varieties with monstrous flowers in colours that would look at home on a Fifties housecoat. This was the point at which, finally, the tables turned, and while the enthusiasm for competitive dahlia growing has always continued, the popularity of the dahlia in the garden went swiftly downhill.
The dahlia today
In the last decade, the dahlia has shaken off its tarnished reputation, thanks in part to the indomitable Christopher Lloyd, who boldly replanted the rose garden at Great Dixter with a colourful mix of dahlias, cannas and other exotics. 'Dahlias spell excitement,' he wrote, 'and we can all do with some of that in our lives.' Dahlias are arranged into several groups according to their flower shape, from the small, neat pompons to the explosive cactus varieties, and there are hundreds of varieties to choose from. You only have to look at the website of the National Dahlia Collection to see how many there are.
Where to buy dahlias
The National Dahlia Collection sell their astonishing collection of rooted cuttings by mail order until the end of March. They grow over 1,600 varieties in their 2-acre garden in Penzance which is open to the public from mid-July to the end of September.
Sarah Raven is a figurehead for the dahlia's triumphant return to fashion. She grows a huge number of dahlias in her garden at Perch Hill and sells tubers via her website.
de Jager was established in Holland in 1868 as flower bulb specialist. It maintains its reputation for producing the highest quality bulbs and in 2012 was granted a Royal Warrant as supplier of garden flower bulbs to The Prince of Wales. It sells an excellent range of dahlia tubers, including dinner plate dahlias for show.
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