Dahlias: late summer’s show-offs

From August until the first frost, dahlias are the busiest flowers in an Irish garden. The more you cut, the more they flower, which makes them a gift that keeps on giving to anyone with a sunny patch of ground.

Dahlia in an autumn arrangement — In an autumn mix

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From the mountains of Mexico

Wild dahlias grow in the uplands of Mexico and Central America, and the dahlia is Mexico’s national flower. Seeds and tubers reached Madrid’s botanical garden in the late eighteenth century, and the plant was named after the Swedish botanist Anders Dahl. Breeders in Europe went on to produce the thousands of varieties we have today, in every colour except true blue.

What a dahlia says

Dahlias were not part of the old flower-language books in the same way as roses, so modern meanings are loose: commitment, dignity and the abundance of the end of summer. In practice people give them because they are cheerful, generous and in season.

Flower forms to know

Decorative: broad, flat petals in full, rounded heads, from small to dinner-plate size.
Cactus and semi-cactus: narrow, rolled, spiky petals.
Ball and pompon: tight spheres of curled petals; pompons are smaller and very neat in posies.
Waterlily: open, shallow flowers with fewer, wider petals.
Single and collarette: open centres that bees love, a good choice for wildlife gardens.
‘Café au Lait’: a huge blush-cream decorative variety, a favourite of wedding florists.

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Growing dahlias here

Plant out after the frosts, usually from mid-May, in sun and rich, free-draining soil.
Guard against slugs while the shoots are young; a wet Irish May is their favourite season.
Stake early. Tall varieties snap in autumn gales once they are heavy with flowers.
Deadhead and cut often to keep new buds coming.
Winter: mulch in mild gardens, or lift and store the tubers where the ground stays wet or cold.

Dahlias in the vase

Cut blooms that are nearly fully open; buds rarely open well indoors.
Put them straight into deep water and leave them somewhere cool for a few hours before arranging.
Strip most of the leaves and refresh the water every day or two; dahlias foul water quickly.
Expect about five days to a week. Pompon and ball types tend to last longest.

For other late summer favourites see sunflowers and peonies, and for general advice our care tips. Meanings of other flowers are in flower language.

Dahlia at a glance

Question	Answer
Botanical name	Dahlia
Native to	Mexico and Central America
Flowering in Ireland	July to the first frost
Vase life	About 5–7 days

⚠️ Pets: Dahlias are mildly toxic to cats and dogs and can cause a mild upset stomach and skin irritation if chewed. Keep bouquets and stored tubers out of reach.

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Dahlia questions

Do I need to lift dahlia tubers in winter in Ireland?

In mild coastal gardens with free-draining soil, many people leave them in the ground under a thick mulch. On heavy, wet soil or in colder inland areas, lift them after the first frost blackens the leaves, dry them off and store them frost-free.

Why do my dahlias have holes in the petals?

Earwigs are the usual culprits, feeding at night. Slugs attack the young shoots in spring. An upturned pot stuffed with straw on a cane traps earwigs, and protecting new growth from slugs early on makes a big difference.

When should I cut dahlias for the vase?

Cut them almost fully open, in the cool of the morning or evening. Unlike many flowers, dahlia buds rarely open properly once cut, so wait for the bloom you want.

Are dahlias poisonous to pets?

They are listed as mildly toxic to cats and dogs. Eating them can cause a mild upset stomach and skin irritation, so it is best to keep bouquets and tubers out of reach.