Dahlias: how to grow beautiful dahlia flowers (original) (raw)
The small, apricot flowers of Dahlia ‘Maldiva’Eva Nemeth
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.’
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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.
Rachel Siegfried in the cutting garden at her flower farm.
Eva Nemeth
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.