How to grow dahlias: expert plant care and growing guide

(Image credit: Wouter Koppen/Ibulb)

published 23 February 22

If you're wondering how to grow dahlias, then you've come to the right place. After falling out of fashion for a while, these beautiful blooms have staged a big comeback and their newfound popularity shows no sign of waning. After all, these incredibly varied plants offer something for everyone.

Dahlias are totally versatile, too – you can plant them in borders, grow compact cultivars in containers, or treat them as a cutting-flower crop for show-stopping displays indoors. They can also be very good value for money – a single dahlia tuber can produce blooms from the middle of summer right through to the first frosts.

Whether you want to fill your flower bed ideas or just test out one or two varieties of these stunning blooms in pots, they're a fail-safe option for gardens big and small.

'Anyone who grows dahlias will know they start flowering in mid summer but are at their best during late summer and fall, delivering masses of bloom right up until the first frosts,' says Amateur Gardening's Anne Swithinbank. 'Originally from the uplands of Mexico and the narrow strip of countries where North and South America connect, these equatorial plants enjoy plenty of sun, cool weather and hit peak performance when the hours of night and day are similar. Plant dahlias and you will have a brilliant late show in the garden and masses of blooms for cutting.'

Pom pom dahlias — *Pompon dahlias will instantly elevate a border*

How to plant dahlias

Dahlias, which grow fresh from tubers every year, aren’t very good at pushing up through herbaceous plants. So, if you're growing them in a garden border, it's best to give them their own bit of space.

However, there are also some that are perfect for growing in pots as part of your container gardening ideas. These will look stunning lining a path or for a striking patio display.

'Planting tubers around 4-5in (10-12cm) deep in prepared ground during mid spring is the most straightforward method,' says Anne Swithinbank. 'Remember though that dahlias dislike crowding and need space to develop. If you want earlier flowers, plant tubers in pots under glass in early spring for planting after danger of frost.'

Garden expert Tamsin Hope Thomson for Amateur Gardening shares her top tips for planting dahlia tubers:

Pick a spot which gets plenty of sun (especially important if you want to leave the tubers in the ground over winter), with well-draining soil.
If you're using a container, make sure you use a rich compost.
Dig a square hole around 12in (30cm) wide and deep, and space out your tubers about 24in (60cm) apart.
Then fill back up with compost. Keep the compost on the dry side until signs of growth appear, then water more frequently.
The most successful dahlias also have a good supply of well-rotted manure placed around the base soon after planting. Whether you've done this or not, the plants should also be fed every few weeks throughout the growing season. Alternate between a seaweed tonic and a potash-rich tomato feed.

how to grow dahlias pink flowers — *These bright pink beauties are bound to turn heads*

Growing dahlias from seed

'Growing dahlias from seed is a great way of enjoying plenty of plants cheaply and easily,' says Anne Swithinbank.

'To grow flowers from seed, sow seeds thinly and evenly in spring, cover very lightly with compost or vermiculite and germinate at 65˚F (18˚C). Transplant seedlings singly to pots, grow on and plant outdoors in late spring or early summer. Go for something like ‘Bishop’s Children’, which delivers a pleasing mixture of single flowers against dark foliage, plus you can save the tubers of favourite colors.'

woman sowing dahlia seeds in a seed tray

When should you plant dahlias?

Dahlias are tender plants, so it's important to keep them protected from frosts. Because of this, it's generally best to start tubers off undercover in your greenhouse, or even a DIY cold frame in early or mid spring. Then plant them out once the temperatures outdoors are reliably warmer – generally around late spring to early summer.

Remember to harden them off before planting, by standing the pots outside in the garden for a week or two so they can gradually acclimatise to the outdoor conditions.

How to care for dahlias

The beauty of dahlias is that they're not overly demanding, so can be added to your plot as part of your low maintenance garden ideas. However, they do require the right care at the right time to keep them happy.

During the summer and early fall months you will need to water them regularly throughout dry spells. Remember to feed them, too.

Don't be afraid to cut flowers off for displaying indoors because this will actually help your dahlias. Regular picking encourages them to keep on producing flowers – what a win! Deadheading flowers regularly is also advised, plus make sure you check for pests and signs of other disease.

cactus dahlias — *If you want to learn how to grow dahlias, the cactus variety makes a striking choice*

Staking dahlias for added support as they grow

Some dahlias are taller than others, which means they'll need a little more support to stop them from toppling over. It's worth knowing these tips:

Dahlias can be very brittle at their base, meaning whole stems are easily broken if it's windy.
Ideally, plants should be staked at the time of planting in late spring to early summer.
Use bamboo canes to support the plants and tie the stems with twine at 12in (30cm) intervals. If you haven't done this already, make sure you do so as soon as possible, as your dahlias get taller.
Be careful not to damage the roots as you insert the canes, and make sure they are as close to the plant base as possible.
Larger plants may need several stakes. Continue to tie in the stems as the plants grow taller for added support.

Taking cuttings from dahlias

Gardening expert Ruth Hayes of Amateur Gardening shares her step-by-step tips for taking cuttings from dahlias.

As with all flowers, taking cuttings from plants is a fantastic way to get new plants for free – ideal if you're after cheap garden ideas.

Mix seed compost with perlite in a four inch clay pot, then add a little water to dampen it.
Using a clean knife or your best secateurs, remove just a few strong shoots from your dahlia plant, each at about 4in (10cm) in length.
Remove the lower leaves, otherwise they may rot when you pot your cuttings up.
Dip the ends of your cuttings in rooting compound – this will help to promote strong and healthy root growth.
Insert the cuttings into the compost and perlite mix and carefully firm them in.
Seal the newly potted cuttings in a plastic bag and place somewhere light and warm – such as in your greenhouse or on a sunny windowsill. New roots will soon begin to develop.

dahlia cuttings in pots — *It's worth learning how to take cuttings from dahlias so you can get lots more plants for free*

How do you get bigger blooms on your dahlias?

To get good, long dahlia stems and larger (but fewer) flowers, cut off all side growths 24in (60cm) below the growing tip. This allows plenty of stem for cutting these if you want to arrange them in vases indoors. And it also allows lower shoots to go on growing to produce replacement stems.

Another tip to ensure show-stopping blooms is to retain just the top bud and pinch out all the other flower buds immediately below.

how to grow dahlias: pink pompom — *A pink pompon beauty*

What should you do with dahlias in winter?

'In colder regions and for ease of management, it is best to lift tubers after foliage has been blackened by the first frosts,' says Anne Swithinbank. 'Dry and store them frost free covered by slightly moistened old compost or sand.'

Tamsin Hope Thomson for Amateur Gardening offers these step-by-step tips for storing dahlia tubers:

Wait until the foliage has turned black from the frosts, then cut the plant down to about 6in (15cm).
Lift the tubers and brush away the soil with your hands.
Leave them to dry for a few weeks in a shed or indoors.
Then store in a box of compost of sand over winter, before replanting the following spring.

If you're in a warmer part of the world then you don't have to lift the tubers. 'In milder regions dahlias can withstand most winters in the ground under a dry mulch of leaves or bark,' explains Anne Swithinbank. 'However, they might be late into flower and sometimes large, old tubers lose vigor.'

If you're going to leave tubers in the ground, the best method is to simply cut back the plants and then apply a layer of mulch or compost to the crowns for extra insulation. Our guide to mulching has more info should you need it.

lifting dahlia tubers in winter — *Cut back the main stem to leave a stalk before lifting the dahlia tuber*

Problems to look out for with dahlias

As with most plants, a few pesky problems can arise. Here's a few to look out for:

Dahlias can be prone to pests including snails and aphids, so check them regularly for signs of infestations. Pick off snails or catch them in beer traps. You can use chemicals to get rid of aphids, but a more environmentally-friendly option is to introduce natural predators such as ladybirds and hoverflies. Our guide on how to get rid of aphids is full of useful advice.
Earwigs can also be a pest to watch out for when learning growing dahlias. You can collect them in simple paper traps. Crumple up newspaper and place in an upturned flower pot which can sit on top of your stakes. This attracts the earwigs and keeps them off the plants.
Diseases such as powdery mildew can be a problem for dahlias. You can improve your chances of prevention by removing dead and damaged foliage before it starts rotting and by creating good airﬂow around plants.

Where to buy dahlias

In summer it's easy to get hold of potted up dahlias that are already in full growth. Alternatively, in spring, you can buy bagged up tubers from garden centers or online.

You can also pre-order tubers and rooted cuttings from specialist nurseries for an early spring delivery. However, make sure you've got a frost-free place like a greenhouse with heating or use insulating fleece when starting them off, depending on how cold it is.

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Teresa Conway

Teresa has worked as an Editor on a number of gardening magazines for three years now. As well as holding editorship of Easy Gardens magazine and Woman's Weekly gardening she has worked as the gardening specialist on a number of home magazines including Homes & Gardens, Country Homes & Interiors, Ideal Home, Living etc and Style At Home, so she is lucky enough to see and write about gardening across all sizes, budgets and abilities.

These years in the industry have meant that she has developed close working relationships with top garden designers and landscape architects having access to their projects and and expertise. Attending industry events such as Chelsea Flower Show and other garden openings and launches. Last year she was on the judging panel for the Society of Garden Designers awards and she continues to be this year too.

She recently moved into her first home and the garden is a real project! Currently she is relishing planning her own design and planting schemes. What she is most passionate about when it comes to gardening are the positive effects it has on our mental health to grow and care for plants. Keeping our patches alive with greenery is great for the environment too and help provide food and shelter for wildlife.