Here’s a masterclass on growing dahlias courtesy of some of our favourite gardening bloggers, YouTubers, and Instagrammers. When it comes to dahlias, not only do these growers know their stuff, but they’re also happy to share their knowledge and experience. Whether you want to plant dahlia tubers or raise them from seed, this is the place to start.
Best advice on the different types of dahlias
A flower with countless variations, dahlias take their name from the Swedish botanist, Anders Dahl who lived in the mid 1700s, says pro gardener Annabel Bridge at North Leeds Garden Design. Originally a native of Mexico, Annabel explains that dahlias are, “closely related to the daisy and the sunflower,” with blooms made up of “numerous delicate petals surrounding a central core.” Read Annabel’s full article about the wondrous world of dahlias to find out why so many people develop an obsession with these special flowers.
There are currently 15 recognised groups of dahlias ranging from the single flowered varieties (group 1) through to the stellars (group 15). Offering a full illustrated explanation of the properties of each group, BBC Gardener of The Year finalist, Martin Cole from Gardening Step-by-Step explains each of the different types of dahlias along with suggestions for some of the most special cultivars to try.
Best advice on growing dahlias from tubers
“When your dahlia tubers arrive, they will look like big, dry salamis,” says Kendall Turner from Bloom Sheffield. If you’re wondering just what you should do with them, Kendall recommends storing your dahlia tubers until all risk of frost has passed, or, follow her preferred route and “pre-sprout them in a greenhouse a little earlier to get them big and strong before they go outside.”
As soon as your tubers arrive, give them the once over, checking to make sure that they’re not too squishy. Each one should have a ‘collar’ at the end of the neck – the long tapered part of the tuber – and this should have a dark spot on it. This is called an eye, and without it your dahlia won’t grow, says Hannah Miller at DIY Gardening. She recommends storing your dahlia tubers in compost, in a cardboard box with ventilation holes cut in the sides. Check out her excellent post for more details.
“You MUST stake when you’re planting, not afterwards,” says Nicole Laird @nicoleatcherrygarden. Otherwise, “there’s a real risk of you staking a tuber which could lead to lots of nasty things that could affect your dahlias.” Do take a look at Nicole’s Instagram story on planting your dahlia tubers in 5 litre pots in the ground. Not only does this make them easy to dig up in the late autumn, it also helps to protect your dahlias from gall, a common bacterial disease which can decimate your precious blooms.
One great way to grow dahlias is to build a special raised bed and support system. That’s just what Mars and Kirsten @my.home.farm.uk have done. Not only does it provide a protected growing space for your dahlias, but the overhead support system negates the need for bamboo stakes which can blow over. This looks neater and makes it easier to cut dahlias for your indoor displays. Head over to Mars and Kirsten’s Insta to watch Mars build the raised bed and special supports.
Best advice on growing dahlias from seed
Watch as Lee from the perennially popular YouTube gardening channel, Project Diaries, demonstrates how to grow dahlias from seed. Always keen to reuse and recycle, here he uses an old clear plastic chocolate eclair box as a simple propagator and places it on his windowsill. It takes just five days for some of his seeds to germinate ready for transplanting into their own pots – check out Lee’s video to see how he does it.
Over at YouTube channel Happy Sowing Happy Growing, Paul Machen plants his dahlia seeds on a bed of compost with a scattering of vermiculite over the top before watering in. After a few days in his heated propagator at 22C, the seedlings are ready for potting on. If you’d like to see how he goes about potting his dahlias into multi-cell trays, do watch his video which takes you through the process step-by-step.
Best advice on growing dahlias in pots
If you’re intending to grow dahlias in small pots, do make sure you select bedding dahlias, says John Moore over at Pyracantha. That’s because some varieties of dahlias grow very tall. That said, John agrees that you can grow bigger dahlias on your patio provided you choose a big enough container and stake them when planting. His top tip – if you’re planting in pots, make sure you water: “They prefer to be soaked down occasionally, rather than watered little but daily.”
For a thorough run down of the ins and outs of planting dahlias in pots, we also recommend these 10 top tips for growing stunning dahlias in pots by Hannah Miller over at DIY Gardening. She says one of the best ways to ensure lots of incredible blooms is to pinch out, or use a pair of secateurs to cut out, the centre stem. According to Hannah, the opportune moment is “when the dahlia has four sets of leaves (when it’s roughly a foot tall).”
Do remember, whether you’re growing your dahlias in pots or in the ground, these flowers are a ‘cut and come again’ plant. If you don’t deadhead dahlias regularly, they’ll consider that their work for the season is done, says dahlia enthusiast Jo Manser from Produce From The Garden. But be careful when deadheading, says Jo: “Clip the pointy spent buds, the dome shaped buds are about to flower.”
Best advice on overwintering dahlias
Dahlias are tender perennials and so shouldn’t stay in the ground during the winter for the frost to get them. Instagrammer, Tessa @livingthegardendream offers some great and simple advice for overwintering dahlias: “When the frosts blacken the foliage you cut it back and gently lift them, turn them upside down to dry, clean them up and store them somewhere dry and frost free over winter.”
Over at Homegrown and Hopeful, Laura says she’s been growing dahlias every year since she first tried propagating a batch on top of her radiator with incredible success. Her overwintering technique for dahlias is simple and straightforward: “We dig up the underground tubers when they finish flowering and bring them into a dry area. If you have space, you can put your tubers into dry sandy soil or sawdust to keep dry and frost free.”
While there’s some debate about exactly when you should dig up your dahlia tubers for overwintering, Hannah at DIY Gardening is in no doubt about the best strategy for her. She waits until after the temperature takes a dive because, “the tubers need to swell up and mature before they’re lifted, and this usually happens after the first frost.” She explains that if you pull them up too early they’ll be green. “This means finding the eye will be difficult, making dividing them near impossible.”
If you live somewhere where the winters tend to be mild – the South West of the UK, for example, you may not need to dig up your dahlia tubers at all. Marie from Plews Garden Design offers the following advice on her Insta feed @plewsgd: “In well drained soils in mild areas, dahlias stand a good chance of overwintering in the ground. So you need do nothing.” In this case, applying a thick mulch should be enough to prevent heavy frosts from damaging them.
Over at The Middle Sized Garden, blogger and dahlia grower Alexandra is very much in favour of not digging up dahlias. She says each autumn, she piles as much compost on top of her dahlias as she can and marks the spot with a stick so she knows where they are. She lives in the south and says most of her dahlias survive, though not all. Do check out her blog to see which varieties make it through the winter frosts.
Best advice on caring for dahlias and deterring pests
Slugs and snails are the number one dahlia pest, says Alexandra at The Middle Sized Garden. Having turned to a professional organic gardener for advice, she says managing these slimy pests is possible without using harsh chemicals. She advocates a two system approach – wool mulch and organic slug pellets made from ferric phosphate which stops slugs in their tracks but won’t harm garden birds and animals.
Because dahlias require quite heavy watering, you might wish to take a leaf from the book of YouTuber Annette over at CottoVerdi. Do check out her video showing how to prepare a dahlia bed complete with an irrigation system. She says, not only does this save a lot of bother, it’s also a great way to avoid wasting water as you’re watering the roots directly and not wetting the petals and leaves which can turn rotten and soggy.
Growing dahlias is one way to guarantee a brighter, bigger, bolder flower display in your garden this season, and because they make such wonderful cut flowers, it’s also a great way to bring the beauty of the outdoors into your home. We hope you’ve enjoyed our pick of the best online advice on growing dahlias – now all you need to do is decide which cultivars to grow this spring.
Choose from our full range of dahlia tubers – or, if you’re looking for dedicated growing advice and expert gardening tips, head over to our dahlia hub. You can find lots more information about keeping your garden looking beautiful this summer on our summer flowers hub page.
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