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Plant dazzling dahlias for a summer of colour

Jennifer Stackhouse

Jennifer Stackhouse

November 15, 2016

We did a roaring trade in dahlia tubers at our local flower show at Sheffield in Tasmania in October. Club president Paul Robinson arrived with a picture of a burgundy and white Collarette dahlia and a rubbish bin full of damp compost and sprouting dahlia tubers. They were the result of lifting and dividing several clumps from his garden.

Colourful Collarette dahlia

Colourful Collarette dahlia


At just a dollar a tuber and the promise of gorgeous red and cream flowers, I spent a lot of the day up to my elbows in compost finding tubers for eager gardeners.

Majestic eye-catching dahlias in the late summer garden

Majestic eye-catching dahlias in the late summer garden


Dahlias are flowers of summer and autumn but, like tomatoes, are planted in spring or early summer after all threat of frost has past. According to gardening lore this magic date for most of southern Australia is after Melbourne Cup Day (the first Tuesday in November), but tubers can be planted from mid October until early December or from late spring to early summer.

Wonderful array of dahlias in toning colours

Wonderful array of dahlias in toning colours


How to plant dahlia tubers

Dahlias grow from elongated rather ugly looking tubers. At one end of the tuber (known as the ‘neck’ or ‘nose’) shoots appear from ‘eyes’. These are the growth points that form at the base of last season’s stem.

Tubers are planted in a sunny, sheltered spot. Full morning sun and afternoon shade is ideal. Show-quality dahlias are grown under 50-per-cent white shadecloth to prevent the flowers burning. To enrich the soil to fuel all that furious growth, dig in well-rotted cow manure before planting.

Tall Delbard Dahlia 'Bangkok'

Tall Delbard Dahlia ‘Bangkok’


Lay the tuber horizontally with the shoots upwards. The tubers should be buried 10cm deep. As these are tall plants (some varieties are 2−3m high) with brittle stems, the combination of sun and shelter is vital for good growth. Even with shelter, staking is recommended. Use a tomato stake, trellis or a perennial support frame. Put the stake into position then planting the tuber beside it with the neck close to the stake.

Dahlia 'Chandenagor'

Dahlia ‘Chandenagor’


For gardeners who don’t like the idea of a garden full of stakes, dahlias can be trained on a trellis or supported with perennial frames. Alternatively grow dahlias as cut flowers in the vegetable garden where a row of stakes doesn’t look out of place. Space them 30cm apart. In the garden, dahlias mix well with roses and herbaceous perennials.

As the dahlias shoot and grow, apply a complete fertiliser. As the stem forms, tie it carefully to the stake and keep adjusting the ties as the stem grows. Tip pruning now keeps the plant more compact. Keep plants well watered right through summer.

Old fashioned tall dahlia (name unknown)

Old fashioned tall dahlia (name unknown)


The first frost brings these cold-sensitive plants to a halt. Cut down old growth in late autumn. Tubers are lifted and divided in early spring. Left undivided, plants re-grow each year but the clump becomes large and flowers get smaller.


Dahlia history and hybrids

Dahlias were introduced to horticulture from Mexico in the late 18th century and were growing in gardens in Tasmania by 1838 when the first dahlia was exhibited at Launceston.

Pink single lollipop dahlia

Pink single lollipop dahlia


Early dahlias had single flowers but after centuries of breeding and selection, modern dahlias have large, full flowers in vibrant colours including yellow, orange, red, brown, pink and white. Some are multi-coloured.

There are 10 categories for hybrid dahlias but most are doubles some with broad flat or spiky, tubular petals. Not all the flowers are huge. The Pompon group has small balls of flowers on stout stems.

Small dahlia cultivars don't need staking

Small dahlia cultivars don’t need staking


Popular in gardens today are single-flowered varieties with red, yellow or orange flowers. ‘Bishop of Llandaff’ is a single-flowered form that helped bring dahlias back into general popularity. It has bold red single flowers and red-tinted leaves.

An exciting planting composition using Dahlia 'Bishop of Llandaff'. Design Carolyn Blackman Vivid Design, Melbourne

An exciting planting composition using Dahlia ‘Bishop of Llandaff’. Design Carolyn Blackman of Vivid Design, Melbourne


Another variety that fits with modern gardens is ‘Yellow Hammer’, a tall single yellow dahlia, while the variety ‘Le Coco’ has yellow single flowers with a vibrant orange centre.

Pots of these popular single varieties may be available at garden centres in summer in bloom for those who miss planting time. Dahlias will also be on show and for sale at late summer and autumn flower and dahlia shows.

Dahlia garden in Christchurch

Dahlia garden in Christchurch


[This article first appeared in TasWeekend (October 29-30, 2016) in The Mercury.]

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7 years ago

Hi Jennifer,

I came across your article about the poinciana tree. Has it flowered this year? Could you please give me the name of the street in Kurmond so I could pay it a visit? I came from a tropical city where poinciana is the tropical version of Sydney’s jacaranda trees. When you see that red blanket covering the canopies, you know summer is near and it’s school exam time …