Dahlias are amongst my favourite flowers. Here I describe how to grow dahlias if you’ve never done so before.
Most of my novice gardener friends assume dahlias are beyond their skill. Maybe the mesmerising petal formations and dazzling colour variations confuse dahlia debutantes into thinking that they are hard to grow. They are not.
Coming in a variety of colours wider than Jackson Pollock’s palette, there is a dahlia out there for everyone. Dahlias have bounced back from the days when they were considered the brash gatecrasher at a debutante ball. They’re everywhere on social media in late summer and autumn – and deservedly so – but you need to plan ahead and buy your tuburs in winter if you want to grow your own stunners.
A dahlia laden with flowers and buds has great impact in the garden, and nothing is more beautiful in the autumn home than a tastefully combined bouquet, or even a brash clash in a mixed arrangement. It is rare to find them in any variety in your average florist and often not at all. The answer is to grow your own and now’s the time to shop for the ones you want before they sell out.
My dahlia story – how I learned to grow dahlias
My love affair with the dahlia began in the late 1990s when we moved to a terraced house in SW London with a tiny courtyard garden. I’d planted architecturally strong plants such as tree ferns, banana and palms. I wanted some flowers too but was a bit stumped for ideas.
Remember this was before pinterest and instagram. In the pre-broadband days of the dial-up modem we weren’t in the habit of internet inspiration. A magazine article suggested combining high impact leaves with the knock-out colour of dahlias and I went for it. I wasn’t sure how best to grow dahlias but I knew I’d figure it out.
This was at the early stages of the dahlia’s comeback as a garden flower and they weren’t widely available. I bought what was on offer in my small local garden centre, potted them up in my kitchen and waited for them to do something.
A few weeks later I was about to give up when I saw what looked like bulging bronzed pink nodules at the base of the brown stem. They were off. By late May, I had a few healthy looking plants and had even been brave enough to take some cuttings, all of which rooted.
I have no recollection which varieties I grew that first summer and the colours were, with hindsight, rather nasty; a two tone orange semi-cactus type and a garish all yellow small cactus. But you need a loud-mouth plant to keep company with bold banana, tree ferns, Crocosmia ‘Lucifer’ and acid Nicotiana ‘Lime green’ and my hot coloured dahlia more than held their own.
I now have a larger garden in the Chiltern hills and I still have what I call a ‘tropical border’ with banana and trachycarpus fortunei. Every year these are joined by different dahlia and zinnia, all in hot club tropicana colours.
Last year, in another flowerbed, I branched out from my hot colour schemes and combined soft pink, white and dusky-rose dahlias with lavender, pink and mauve perennials and cool acid green flowers and thyme.
Choosing which dahlias to grow
The revival in the popularity of the garden dahlia is due in some part to the inventiveness of garden creators such as Christopher Lloyd and Felix Garrat at Great Dixter. They showed that colour clashes can be good. Garden blogger Out Of My Shed has written a great article about inspirations from Great Dixter and sourcing dahlia tuburs.
Tubur suppliers have trialled varieties in garden and cutting patch settings. Trialling them on their own and alongside other plants they have derived colour collections that you can easily replicate at home. Sarah Raven plants really have their finger on the dahlia zeitgeist and sell many collections. Peter Nyssen are selling a 6 dahlia selection in hot colours for £12.50 and make suggestions of perennials to plant alongside in a mixed border. If you’re a newbie, collections put together by others are a great starting point and once you get your confidence up you can experiment with your own blends. I have also bought excellent quality dahlias from Gee Tee Bulb company, who sell many great varieties and a mixed collection for a cutting patch or allotment.
Another great starting point is to look at gaps in your border and consider which dahlia will stun in that location. Do you need a taller variety? One with small flowers? and which colour will charmingly blend or cunningly clash with what is already there? Take time to look through catalogues. You’ll soon narrow down the options but I doubt you’ll resist the odd tubur that you’re yet to place.
Where to buy dahlias
Tuburs are now widely available from stores and online. I have bought many from online suppliers, garden centres and even from supermarkets.
The advantage of buying in a garden centre is that they are often in see through breathable plastic bags so you can take a look at the tubur and check that it isn’t damaged. Sometimes the fleshy food-storing parts of the tubur will have twisted off.
Bear in mind that not all tuburs will be the same size. Paying a bit extra for a large, healthy tubur, from a reputable online supplier may pay dividends for a stronger plant.
How to grow dahlias that are loved by bees (but also earwigs)
Generally speaking, dahlias with single, unfussy petal structures – where the nectar and pollen are easy to access – will be more attractive to insects. If you want to attract pollinators such as bees and hoverflies to your garden then do choose single varieties.
Insects you don’t want near your dahlias are earwigs as they nibble the petals and ruin the look of the flower. Putting an upturned pot of straw on a stick nearby will give the earwigs somewhere to hide but it’ll only help if you’re wiling to empty and dispose of them each day. Otherwise you’re simply providing a luxury earwig hotel with gourmet restaurant nearby.
How to plant your dahlias
Whilst dahlias are on sale in garden centres and online from mid January, it’s inadvisable to do anything with them until late february or march. The tuburs will have been carefully washed and dried and will come to you stored in paper or plastic bags with sawdust or dried compost. They are dormant and you don’t need to worry about dealing with them until conditions are right for you. Just keep them in a cool dry place and they’ll be just fine.
If you like, you can wait and plant them straight out in the garden (with a fair dollop of manure) once the chance of frost has passed. But if you want slightly earlier flowers, or to get some cuttings underway, it’s worth potting them up and bringing them on sooner.
If you have a greenhouse then keep them there so long as you know they won’t get damaged by frost in really cold weather. If in doubt, bring them on in the house.
- Unpack your Dahlia tuber and check it over. Each part of the tuber should be firm. Any shrivelled or rotting pieces should be taken off and discarded.
- Tubers vary significantly in size. Take a look at your tuber and work out which size pot it will fit into. To save on compost, choose the smallest pot that will fit your tuber. Fill the pot to a third full and place your Dhalia on top of the compost. You should be able to see which way up the tuber goes as the remains of last year’s stem is usually visible.
- Add more compost around the tuber and tap the pot frequently to settle the compost around it. It needn’t be fully covered and leaving the stem and top f tuber showing can help you see when it’s starting to shoot. Water and keep moist, but not wet, in a greenhouse or on a windowsill.
- Tubers vary in how quickly they come into growth. Generally speaking you should see small bulges developing on the tuber within a month but some will take longer. Heat from below (a heat mat or propagator) can be beneficial to bring a Dahlia into growth sooner.
- Pinch out the tips of the growing stems to encourage bushier growth – don’t be scared to do this – you’ll get more flowers.
- Do not plant outside until you know there will be no frost. Dig in some compost and manure before you plant and consider feeding with chicken manure throughout the growing season.
- Pick your flowers regularly and deadhead those that have gone over – again, you’ll get more flowers that way.
This is the only tricky thing about growing dahlia and I’ve saved it to last so as not to put you off. It’s very much a judgement call. What we do know is that they will rot outside in cold, damp winters. The question is how damp and how cold? What kind of weather will we be in for in any one winter? Can you afford to replace any lost tuburs? and have you the room or environment to store them correctly over the winter?
No garden or gardener’s resources are the same so it’ll be a decision you must take alone. Helpfully the Middle Sized Garden blog produced an excellent article summarising the dahlia overwintering dilemma. It’s well worth reading to help you make your mind up and makes reference to the fact that some types of dahlia may succomb more easily to winter than others.
My experience of the dahlia dilemma is mixed. I spent the first few years as a dahlia grower digging up my tuburs, washing them off, drying them and storing in a dry shed. This was in London, in a very sheltered garden and with hindsight I really don’t think I need to have bothered. I’m pretty certain they would have survived outside and grown to be bigger, stronger plants with a great root structure if I’d been more laid-back and just let them be.
When I moved to the Chilterns, the dahlia moved with me and I lost a few that first winter, as my new shed was not only cold but very damp and full of mice and possibly rats, which appear to love nibbling on dahlia tuburs. They decimated my stock.
Next year I dried them much more carefully to prevent rot and placed them in onion bags hung from the rafters of my drier garage to fool the mice. It worked and they all survived but it was a labour of love and hardly an advocate for an otherwise easy to grow plant.
2017 was the first year I dug none up but covered them all in a thick mulch layer of loose home made compost in late autumn. As I write this, temperatures are due to drop to -5 overnight and we also had a cold snap and deep snow in December. I am not sure whether they will all survive but I’m optimistic as they are in well drained soil with their mulch duvet to keep them from the cold. Only time will tell but in the mean time I have treated myself to an order of some new varieties. I am a dahlia addict after all!
Summer 2018 UPDATE – I estimate that 90% of the dahlias I left in the ground have sprung up despite the very harsh winter and there is still time for a few more to do so. I have found that the biggest problem with overwintering in the ground is that the slugs and snails LOVE the new growth so if you do try this method, make sure you’re prepared with slug protection. If you don’t like slug bait, which is something I for one am reluctant to use, then keep a close eye on your plants as they emerge and pick off the slugs and snails at night. You only need to do this for while until you have strong growth.
How to take dahlia cuttings – flowers for free
Dahlias are the first flowers I ever took cuttings from. Each tubur send up multiple stems, some of which you can take as cuttings. It’s also advisable to pinch out the growing tips of each stem to make a bushier plant and some of these can also root if handled correctly.
Click here for an article which shows you a step by step guide. It also contains a little youtube video which illustrates just how easy it is.