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Home & garden.

Updated: 10 May 2022

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 Thomas
Dahlia

The flower types and colours of dahlias are wide ranging, from simple singles through symmetrical balls to crazy cactus blooms, and from white all the way through the spectrum to deep red and purple. 

They 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

JanuaryFebruaryMarchAprilMayJune


POT UP TUBERSTAKE CUTTINGSPLANTPLANT
JulyAugustSeptemberOctoberNovemberDecember

FLOWERINGFLOWERINGFLOWERINGLIFT TUBERS

Best dahlia varieties

Which members can log in now to see the full results and which are our Best Buy varieties. If you're not a member, join Which? to get instant access.

Full testing results for dahlias

Pale-coloured dahlias

Variety nameOverall ratingFlowering durationFlower impactDisplay impactShape of plantsWeather resistancePests & diseasesVase life






USING THE TABLE 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 nameOverall ratingFlower durationFlower impactPollinator attractionFlower coveragePlant vigourPest & diseases resistance







USING THE TABLE 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.

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.

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 fertiliser. Put them in a coldframe for hardening off before planting outdoors.

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. 

Planting

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

Planting dahlia

Deadheading

Keep on top of deadheading to encourage more flowers. 

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.

Preparing dahlia tubers for winter

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 slugs and snails.

Earwigs

Earwigs can nibble the flowers and leave them looking tatty. Shake the flowers to remove them.

Read more about earwigs.

Powdery mildew

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

Read more about powdery mildew.