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08 Jan 2024

How to grow dahlias and the best varieties

Dahlias are stars of the late-summer border. Discover our best dahlia varieties and tips for how to grow them.

Ceri ThomasEditor, Which? Gardening

In this article

Key facts
How to grow dahlias: month by month
Best dahlia varieties
Full testing results for dahlias
Caring for your plants
Common growing problems
How we test dahlias

Dahlias thrive in a sunny spot in fertile, well-drained soil.

They're tender plants so can't be planted out until the danger of frost has passed in late spring, but on light soil their tubers can be left in the ground to flower year after year in late summer and early autumn.

Which? Gardening magazine grew a range of popular varieties to see which would give us the best display.

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Key facts

PLANT TYPE Tender perennial

POSITION Sun

SOIL Well-drained and fertile

How to grow dahlias: month by month

January	February	March	April	May	June
		POT UP TUBERS	TAKE CUTTINGS	PLANT	PLANT
July	August	September	October	November	December
	FLOWERING	FLOWERING	FLOWERING	LIFT TUBERS

Best dahlia varieties

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Full testing results for dahlias

Pale-coloured dahlias

Variety name	Overall rating	Flowering duration	Flower impact	Display impact	Shape of plants	Weather resistance	Pests & diseases	Vase life
'Babylon Brons'
'Bahama Apricot'
'Cafe au Lait'
'Fairway Spur'
'Gallery Art Deco'
'Karma Korona'
'Penny Lane'

OVERALL RATING The more stars the better. Ignores price and is based on: flowering duration 20%; impact of flowers 20%; impact of display 20%; shape/foliage 15%; weather resistance 10%; pests & diseases 10%; vase life 5%.

Single-flowered dahlias

Variety name	Overall rating	Flower duration	Flower impact	Pollinator attraction	Flower coverage	Plant vigour	Pest & diseases resistance
'Ann Breckenfelder'
'Bishop of Llandaff'
'Bishop of York'
'Boogie Woogie'
'Clair de Lune'
'Magenta Star'
'Pooh'

OVERALL RATING Ignores price and is based on flower duration 25%, pollinator attraction 25%, flower impact 20%, flower coverage 10%, plant vigour 10%, pest & disease resistance 10%. Pollinators rating based on how many bees, butterflies and other pollinating insects visited the flowers.

Dark-leaved dahlias

Variety name	Overall rating	Flower duration	Flower impact	Foliage impact	Flower coverage	Staking	Pollinator attraction	Pest & disease resistance
'Bishop of Llandaff'
'Classic Rosamund'
'Dahlegria Tricolore'
'David Howard'
'Fascination'
'Hadrian's Sunlight'
'Happy Single Flame'

OVERALL RATING Ignores price and is based on: Flowering duration 30%, Flower impact 10%, Foliage impact 20%, Flower coverage 20%, Staking 5%, Pollinator attraction 5%, Pests and disease resistance 10%. Pollinators rating based on how many bees, butterflies and other pollinating insects visited the flowers.

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Caring for your plants

Starting into growth

Dahlia tubers are usually available to buy from late February and need to be started off in the greenhouse in a Best Buy compost for raising young plants. Choose pots twice as wide and deep as the tubers, and pot up so the top of the tuber is just below the compost surface. Keep moist until shoots emerge and then water as necessary, feeding weekly with a balanced liquid feed. Put them in a coldframe for hardening off before planting outdoors.

Identify your plants with Best Buy plastic-free labels

Taking cuttings

Once your tubers have sprouted, you want about four or five shoots. Any extras can be used as cuttings. Choose ones that are about 10cm tall, cutting them off at the base with a sharp knife. Trim to a clean cut, reduce the foliage, and insert the cuttings in a Best Buy compost for raising young plants. Seal a clear plastic bag around the pot and keep in a greenhouse or on a bright windowsill. They should root in two to three weeks.

Discover our Best Buy pop-up greenhouses

Planting

Dahlias need rich soil in a sunny spot, so dig in soil improver before planting. Plant out when all risk of frost has passed and setup supports as early as possible, tying in shoots as they grow.

Deadheading

Keep on top of deadheading to encourage more flowers.

Try our Best Buy secateurs

Feeding

Give plants a boost with a liquid tomato feed towards the end of summer.

Cut flowers

Pick dahlias first thing in the morning or in the cool of the evening, choosing flowers that are fully open but with the petals at the back still looking fresh. Cut above a pair of leaves; axillary buds between these leaves and the main stem will develop to give you more flowers. They should last around four days in a vase.

Overwintering

Dahlias are tender and, although on light soils they can be left in the ground covered with a thick mulch, it’s safest to lift the tubers after the first frosts. Cut down the blackened foliage, then lift with a fork. Remove soil and leave the tubers upside down in a cool place to dry. Store in a frost-free place in trays or boxes filled with dry sand, soil or compost.

Common growing problems

Slugs and snails

These two pests both enjoy eating the soft, young foliage. Remove any that you find or use organic slug pellets. Slugs can be tackled using biological control.

Read more about how to get rid of slugs and snails.

Earwigs

Earwigs can nibble the flowers and leave them looking tatty. Shake the flowers to remove them or you can take advantage of their habit of seeking daytime shelter to trap them. They like really tight spaces to hide in. Make traps of pots filled with straw or corrugated cardboard and place this on top of stakes or canes holding up affected plants, or around the base of the plants.Other possibilities are: using lengths of garden hose cut on a slant, hollow bamboo canes, rolls of corrugated cardboard, pieces of sacking placed on the ground, or boards with grooves in them placed groove-side down on the ground. Next morning shake the earwigs out of the traps away from your plants.

Powdery mildew

In late summer, the leaves can get a white powdery coating. It's most common in dry summers.

Read more about how to treat powdery mildew on plants.

How we test dahlias

We selected different dahlia varieties, ordering three tubers of each. Dahlia tubers started to arrive from February onwards. We inspected all the tubers on arrival, checking for any soft or rotten areas and making a note of their condition. We potted up all our tubers at the end of March using a Best Buy compost for raising young plants. We kept them in the polytunnel at the Which? Gardening magazine trial grounds at Capel Manor, north London. During May, we moved our plants to the coldframe to harden off, before planting them into their final positions in a sunny, fertile bed at the start of June. During the summer, we assessed each variety for flowering impact and duration, attractiveness of foliage, and whether they suffered from any problems. We also tested how long they lasted as cut flowers.