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How to: grow dahlias


Dahlias are the new hot-ticket item in the flower garden, lauded for the brilliant clarity of their colour. 


The sweet-potato-like tubers are available now for planting from August to November. Just ensure the risk of frost has passed before you plant. 

Get creative in matching, or contrasting, dahlia colours to other tones in your flower border, and use their height to create tiers of colour. Use pretty flower supports rather than utilitarian tomato stakes and dahlias will have you swooning. 


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Follow these steps to success.

1. Choose a sunny, protected area away from strong winds as these will snap the brittle stems. Dahlias are generally quite tall, well-suited to the back of the garden bed, but make sure they are within reach for picking.

2. Incorporate lots of organic matter, compost and cow manure into the soil before planting.

3. Plant the tubers 10 –15cm deep making sure that the crown points the right way up (see image). Strong stakesshould be carefully placed around your tuber at planting time to offer support to the developing stems. Paint tomato stakes in colours to match the flowers, or have a look at for other options. Your new plants will emerge and grow very quickly. Mulching will conserve water over the hot summer months.


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4. Tie the stems to the support with soft string and keep doing so while the plant makes active growth. The canopy becomes very heavy, which is the reason for the strong support frame. Flower buds will form at the end of summer and you will have an incredible number of blooms through late summer and autumn. Keep cutting the flowers to encourage more. Water with a liquid fertiliser for increased flowers.

5. Cool weather will bring flower production to a halt. Once the foliage has gone yellow and died back, you can prune back to just above ground level for the dormant winter period.

6. Dahlias can be lifted and divided every two years or so. Label the removed tubers, and store them in a cool, dry place. When spring comes around you can replant. If your winter climate is cold and wet with boggy soil that is poorly drained, it’s advisable to lift and store them each year to prevent them rotting.



Dahlias are hungry plants so be sure to feed over summer with pelletised manure such as Organic Life or Sudden Impact for Roses.

The soft growth of dahlias is an easy target for pests such as aphids and mites. Keep an eye out over summer and treat as necessary with Maxguard.

Towards the end of the season watch out for rust damage on foliage. Control it with Rose Gun.

Mix dahlias with other bedding perennials for best effect. When combined with roses, iris and salvias they really make an impact.

A brief dahlia history

It was 200 years after the Spanish conquistadors fisrt saw the Aztec’s dahlias before the seeds, roots, and plants found their way to Europe. The trigger was potato failure and Empress Josephine hoped these new world bulbs might be a solution. As a food source they were a failure, but when they were planted in the Museum of Natural History in 1802 all of Paris came out to see the wonderful new flower from the New World. They reached dizzying heights of popularity when the impressionist painters, particularly Paul Cezanne, painted their beautiful forms and colours.


Text: Linda Ross


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Author: Matt Carroll