Learning how to grow dahlias is rewarding for any gardener. One of the best blooms for cutting, there is a huge variety to choose from, including intricate, candy-coloured pom-poms, elegant single blooms that look similar to daisies, and double-bloomed cactus types in fiery shades.
With such a wide range on offer, dahlias are well-matched to all sorts of garden trends, whether you prefer a more relaxed style or a formal, modern look. Their dazzling display stretches from midsummer into autumn, and while they are gorgeous in borders, some varieties work well in pots.
Growing dahlias is easier than you might expect. But, for the best results, it's worth getting to grips with a few pointers. For advice, we turned to gardening experts, who share their top tips on planting, maintenance, and more below.
Pro advice on how to grow dahlias in flowerbeds and pots
Dahlias can often be bought in pots from garden centres. But, it's also possible to buy and plant dormant tubers. Whichever approach you go for, you'll find plenty of practical tips in this guide.
When to plant dahlias
It's important to remember these alluring plants won't tolerate cold soil, highlights Charlotte McGrattan, hardy nursery stock buyer at Hillier Nurseries and Garden Centres. So, she notes how it's best to wait until any late cold snaps or frosts have passed before planting them outdoors.
Because of this, many gardeners start their dahlia tubers off indoors, in early spring. To do this, plant the tubers in individual pots, with the tops just below the soil surface, and place them somewhere bright, keeping the compost moist. Ensure the pots have drainage holes.
By the time warmer weather comes around – usually in May – leafy plants will have developed and will be ready for planting outdoors, either in large containers or in flowerbeds. Remember to harden them off, first, to acclimatise them to outdoor conditions. You can plant tubers directly into garden soil at this time, too.
Top tip: Make sure you plant your dahlia tubers the right way up: the growing points should be facing upwards.
How to plant dahlias in borders
Josh Novell, director of Polhill, says it’s crucial to choose a sunny but sheltered spot with well-drained soil for your dahlias.
If you're planting tubers directly, the tops should be just below the soil. Plant dahlias that have already been started off indoors at the same depth as they were growing in their pot.
"Ideally, if you have the luxury of space, you want to place your tubers about 60cm apart to allow them to grow as big as possible," Josh says. Once planted, he advises watering them generously. "Mulching around the plants will help to retain moisture and suppress weeds," he adds.
Gardening expert Sarah Raven recommends inserting a stake to support each plant. "Dahlias grow very quickly once they get going and easily break off at the base, so tie them in securely," she says.
Top tip: Petar Ivanov of Fantastic Gardeners advises adding compost or well-rotted manure to the planting hole for extra nutrients. We suggest learning how to make compost at home and using this, for a more sustainable garden.
How to plant dahlias in pots
While dahlias are stars of the summer border, compact varieties make beautiful patio container plants. Check the final growing size when buying – good options include "Dreamy Kiss" from Crocus which reaches up to 50cm.
Choose a pot that has plenty of room for the dahlia to grow – at least 30cm wide and deep – and fill it with multi-purpose compost. Remember, the tubers should be planted just below the surface of the soil.
Add a slow-release fertiliser, such as Gro-Sure's six-month plant food from Amazon, to give it a boost, place it in a sunny spot, and keep it well-watered.
How to care for dahlias
When learning how to grow dahlias, there are a few key maintenance tips to bear in mind.
You'll need to know how to water garden plants properly, as dahlias need plenty of hydration, particularly during hot weather. They also benefit from regular feeding during the flowering period, using a liquid fertiliser rich in potassium. A fertiliser made for tomatoes, such as Tomorite from Levington at Amazon, should work well.
Annelise Brilli of Suttons recommends pinching out the tips of dahlias when they are a few inches tall. Although this will delay flowering, it will promote more blooms and bushier plants that are easier to stake, she explains. "It also makes them much more manageable if you are growing them in containers."
It's also worth learning how to deadhead plants, as according to Petar, deadheading dahlias is essential for promoting continuous blooming. "Regularly remove spent flowers by cutting the stem just above the first set of leaves beneath the flower head. This will encourage the plant to produce new blooms and prevent it from giving energy to seed production and vegetation."
In terms of pests, Sarah warns that earwigs eat dahlia flowers and leaves. "Control these by filling small pots with straw before positioning them upside down around your dahlias. The earwigs will crawl into the straw in the heat of the day and can then be released far away," she says.
There are also some natural ways to get rid of slugs, which can pose a risk to these plants. Sarah says, "Try harmless slug repellents such as wool pellets or copper bands, which slugs and snails hate." Read more on Sarah Raven's hortiwool slug repelling solution.
Winter care for dahlias
Dahlias are tender plants, so you'll need to help them survive the winter months.
Sarah notes how recent winters in southern England have been milder, so dahlias overwintered in the ground have re-emerged fine, provided they’re mulched deeply. However, she warns that opting for this approach is risky if hard winters hit.
“To overwinter in the ground, wait for the first frosts to blacken your dahlias before cutting them to within 10cm of the ground," she instructs. "Label each dahlia for easy identification, then add a mound of mulch to act as a protective winter duvet."
Although this is a low-maintenance approach, Annelise points out a couple of drawbacks. "The tubers will sprout and flower later, plus those tender shoots are much more vulnerable to slugs and snails." Her gardening tip? "If you are leaving them in, make sure you put down organic slug pellets early on."
Alternatively, you can lift dahlias out of the ground and store them indoors. Sarah says, "After the dahlias’ tops have frosted over, cut them down to 15cm before digging up. Knock off surplus soil and scoop out any loose soil between the tubers, leaving enough to hold them in place.
“Leave the tubers upside down in a crate to dry for a couple of weeks," she continues. "Then pack them away in boxes with dry compost, vermiculite, or dry sand to prevent them from drying out. Store the boxes in a cool, frost-free place and inspect regularly for signs of rotting." You can then replant them the following spring.
FAQs
How do you propagate dahlias from cuttings?
According to Annelise, dahlias have hollow stems which do not root. This means you cannot take cuttings from mature plants as part of your tick-list of summer garden jobs.
"When tubers start to shoot, remove a couple of the young new shoots with a sharp knife, cutting close to the tuber," she says. "The shoots have a solid base and will root in a few weeks."
You can also propagate these plants by dividing tubers that have been planted in containers indoors, once they have shoots. Ensure each section has roots and shoots attached, then pot up each one. Remember to harden them off before planting out, when all risks of frost have passed.
Do dahlias grow back every year?
Yes – provided you winterise your dahlias properly, dahlias will regrow every spring for many years.
What are some recommended varieties of dahlias to grow?
Annelise says, "Dahlia varieties offer a wealth of the rarer sunset colours such as apricot, copper and peach. These colours are a valuable part of the garden palette, which tends to dominate with pink and magenta shades. Sunset tones bring warmth into the scene, whilst still combining successfully with pastel schemes. Dahlia 'Cornel Brons' [available at Suttons] and dahlia 'Sylvia' [also at Suttons] are fine examples."
Single-bloomed varieties of dahlias are good plants for pollinators, as the insects can access nectar from them easily. Try the "Bee-friendly" mix from Suttons.
And, if you're looking for large, creamy blooms, you can't forget about "Cafe au Lait", suggested by Petar. "Cafe au Lait" dahlias are available from Thompson & Morgan.
Looking for more expert advice for beautiful summer blooms? Our guide on how to grow peonies at home is full of practical tips.
