How to Grow Dahlias – A Simple Guide

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The Frustrated Gardener is very much a team effort. Whilst it’s usually me pounding the keyboard, from time to time my partner John, otherwise know as The Beau, contributes a post. Dahlias are his plant passion, so I’ve left this one to him. We hope you enjoy it. If you’d like to learn more about our dahlia collection, visit ‘Our Dahlias‘, a page that’s constantly being added to, showcasing many of the cultivars we grow on our allotment. Later this year we hope there will be even more to share with you.

Dahlias are incredibly easy to grow. They can be grown either from tubers, cuttings or seeds. In my experience, neither one of these options is better than the other for flower production. Don’t let anyone tell you that your plants will not flower in the first year if you grow from seed because I can guarantee you that they will. Whether you opt for tubers, cuttings or seeds, if you take care and look after your dahlias properly, then they will flower in the first year. Dahlias are magnificent in that they will bloom for you all summer and autumn, right up until the first frost …. just support, protect, dead-head and feed regularly and they will do the rest.

The ‘Shed Bed’ at the allotment

By mid-March our attention is turning to the 2022 dahlia growing season. We’ve already ordered more varieties for the allotment and plan to make it even more floriferous than last year. Here’s how you can get started.

Seeds

You can pick up a packet of seeds from any nursery or garden centre. What you must remember when growing dahlias from seed is that each and every single seed is genetically different, even if they originated from the same seed head. Breeders will grow from seed in order to create distinctive new varieties and this can lead to some very exciting (and disappointing) results! With seeds, you never know what you are going to get. If you want a specific colour, flower-form or cultivar, choose cuttings or tubers instead.

Sow dahlia seeds in the usual way by filling a pot or seed tray with peat-free compost. Gently push your dahlia seeds beneath the surface or scatter and lightly cover with compost. If you’re growing in a pot, cover it with a clear polythene bag, held in place with a rubber band or piece of string. If sown in seed trays, cover with a propagator lid. The polythene bag or propagator lid will help to maintain warmth and humidity which are dahlia ‘must-haves’. They will need a temperature of around 70ºF (21ºC) and as much light as you can give them to germinate.

Seedlings generally germinate within a couple of weeks. When the first ‘true’ leaves appear the seedlings are ready to transplant into individual pots. Hold the seedlings by the seed leaves, gently teasing them out of the soil. Transplant them into 10cm pots of peat-free, multi-purpose compost. Firm in very gently and give them a good soak. By mid-May, the weather will hopefully be kind enough for you to harden off your plants by standing them outdoors during the day and bringing them inside at night. You can plant them out in their final positions once all risk of frost has passed – frost is not a friend of the dahlia!

Personally, unless I wanted to specifically seek out new varieties or wasn’t particularly bothered what I got colour wise, I wouldn’t grow from seed. I like to know what my flowers are going to look like and I prefer to plan the year ahead by buying tubers or cuttings. Our allotment dahlia beds have particular colours in each so this option is not really for us, however, I will definitely be doing some dahlia breeding in the future as I would very much like to create my own varieties one day.

Precious dahlias seeds

Cuttings

This is my preferred way of growing dahlias. I like nothing more than going through nursery catalogues, picking out the ones I want (always too many!) and then waiting eagerly for them to appear on my doorstep. You can purchase rooted cuttings from reputable growers such as Halls of Heddon and they usually cost around £3 or £4 each. When you consider that tubers can be sold for £5 to £10 each, this makes them even more attractive as a growing option.

When you receive your cuttings, the first thing you should do is transplant them into individual pots. The cuttings will come with little root balls and they will be in urgent need of food, water and light. Once potted up and watered I would pinch out the main shoot – but only do this once you have 3 pairs of adult leaves. If you don’t, hold fire until you do and then pinch out. This will encourage the plant to grow side shoots and bush out – you don’t want to grow a single-stem dahlia unless you are exhibiting the blooms. You should also pinch out seed-grown and tuber-grown plants.

As with seedlings, you can harden plants off from mid-May, then plant them out in their final position once the risk of frost has completely passed. Of course, you can leave them in pots and place them in a bright, sunny aspect in your garden where they will flower all summer long.

Cuttings of Dahlia ‘Johnnie Ellis’ – a large white cactus variety

Rather than buying cuttings you can, of course, take your own. If you already own tubers and want to propagate more, or know someone who has varieties that you’d like to add to your own collection, then cuttings taken around now are the way to go.

You will need to ‘wake up’ the chosen tubers in late winter by placing them in pots in an area that remains around 65ºF to 70ºF (18ºC to 21ºC) – this takes around 2-3 weeks. Once you see sprouts emerging they need to be moved to a heated greenhouse or indoors under grow lights. In no time at all, you’ll have sprouts that are 3 to 4in tall: this is when you can cut them. Fill a modular seed tray with potting soil, giving it a good soaking. Dib holes in the centre of each cell to aid insertion of the cutting. Using a sharp knife, cut off the sprout where it connects with the tuber, as cleanly as you can. Remove the lower leaves, leaving a clean stem, as any leaves that sit below the soil surface will rot. Dip the bottom inch of your cutting in rooting hormone and then place it in the pre-prepared hole. Firm around the cutting with your fingers. Place a clear, domed lid on your seed tray and position it in a warm, bright environment to promote growth – mist a couple of times a day to stop the cuttings from drying out. In a couple of weeks or so you will have cuttings with enough root to enable potting up. Once they are potted up they will need to go back in a heated greenhouse or beneath grow lights. After about a month they should be big enough to plant out, after the threat of frost has completely passed.

The above sounds simplistic, I know, but it really is as simple as that.

Tubers

This is the growing option that most people will be familiar with. Tubers can be purchased from nurseries, garden centres and reputable specialist growers. Because they’re tubers, all the hard work has been done for you and it is simply a case of planting them in moist compost and then waiting for the first signs of life. Don’t water them until they start to shoot. Plant them nice and deep with a good few inches of soil above the top of the tuber. As with seedlings, once you get 3 pairs of adult leaves, pinch out the growing tip.

To lift or leave them in the ground at the end of the season? This is the age-old question. I am of the opinion that if you live in an area that enjoys a kinder winter climate then there is no need to lift them. Simply mulch deeply and leave them alone, unless you are thinking of splitting the tubers to make more plants. If you experience harsh, cold or very wet winters, then I would err on the side of caution and lift the tubers. Dig them up, clean off the soil, dry them and store in a dark, cool place in old soil, sawdust or straw. They should naturally ‘wake up’ around March time – you’ll see little ‘eyes’ appearing on the tubers and can start the whole process again. This year we have left ours in the ground, protected by a thick mulch. I’ll let you know in a couple of months if that worked!

Planting the ‘Shed Bed’ in late May.

Pests

When thinking about growing dahlias there are two creatures that are never far from my mind – slugs and snails. They are the dahlia grower’s nemesis and the plant’s biggest threat. Emerging at night they will head straight for the new, tender, delicious growth. If left unchecked, they can wipe out an entire border under the cover of darkness. What to do?! Well, there are many options, some that work and some that definitely don’t. You could insert a beer trap in the ground near your plants, which I think is a terrible waste of beer. You could spread broken eggshells around your plants or wrap copper tape around the rim of your pots. My personal choice is an organic pellet that is safe for other wildlife, pets and children. Sprinkle very sparingly around the new dahlia growth as soon as you see it. There is also the ‘pick & chuck’ which is TFG’s personal favourite, although, it is worth noting that these marauding molluscs will return from whence they came much like homing pigeons!

Dahlia Nemesis No. 1 (Yes, that is my booted foot!)

Tips to Remember

  • Dahlias are very greedy! Sprinkle the planting area generously with blood, fish and bone before you plant and then feed every couple of weeks or so with a high pot-ash liquid fertiliser (for example tomato feed) when they have started blooming.
  • Heavy clay or very wet soil is not suitable for most dahlias.
  • Plants need at least 6 hours of sun per day to grow well hence shaded areas are not an option.
  • Give plants 2-3 feet on all sides in order to spread out.
  • Support your plants using stakes and/or jute netting as they get taller – some, like Dahlia imperialis, get to 10 feet tall!
  • Tubers can be split, thus giving you more plants absolutely free!
Me and Dahlia ‘Spartacus’ – a personal favourite

I hope that this post has whetted your appetite and that you will decide to start growing dahlias this year (or even more dahlias than you did previously!). There are many resources both printed and online for help, advice and care of dahlias. Below is an image of some of our own preferred dahlia reading.

Happy Gardening One and All!

The Beau.

Categories: blogging, Dahlias, Flowers, How To, Our Allotment, Practical Advice

Posted by The Beau

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32 comments On "How to Grow Dahlias – A Simple Guide"

  1. A dear, elderly friend carries her old scissors out to the garden early in the morning and snips in half any slug she sees. An easy, no touch method.;-)

    1. I need more experience with tuber division. We are going to lift a few to move them so maybe I should ‘have a go’…..

  2. Hello! I am in the United States and wonder if you are ever troubled by dahlia virus? I’ve had to pull out most of mine and have received diseased tubers from several growers. And, I even got infected seed, and had to throw out all the young plants. Even seed can be virus ridden. I’ve almost given up growing dahlias, except as annuals. It’s discouraging because I love them, especially the singles and collarettes. The disease became rampant here as at first I thought it was mites.

    1. We have been lucky so far with no occurrence within our collection. I seem to remember that there was a lot of Gall around last year but again we have been lucky. Fingers crossed that remains the case!

  3. ‘Johnny Ellis’! I very rarely actually select cultivars that I want to grow, but when I do, they are elusive. I have been wanting the ‘San Jose’ bearded iris for many years, but can not find a source for it. Well, I can wait for ‘Johnny Ellis’ also. I should not have gotten if for this year anyway. I may get ‘Siberia’ also, just because I really like that floral form. What is crazy though, is that, although unlikely, I may actually try a cultivar that is not white! (GASP!) I can not determine what is more adventurous; selecting such a non-white cultivar myself, which I am dreadfully unqualified for, or getting someone else to do it for me. Getting someone else to do it for me may seem like a cop out, but if you think about it, could be . . . interesting.

    1. Well, I just looked at your dahlias rather quickly again, and selecting a non-white cultivar would not be easy. ‘Purple Explosion’ looks interesting and has a silly name that I would like to brag about, but dinnerplate dahlias are SO big! My colleagues know that, not only do I have difficult with color, but that I am none too keen on purple. With ‘Purple Explosion’, I could brag about purple, while actually only contending with magenta. I do not know what magenta is, but is sounds pretty. I think that it is the color of the popular bougainvilleas, which I am very fond of because they are so traditional. ‘Spartacus’ is a dinnerplate dahlia also, but I do like that simple rich red! Well, there is time to figure it all out.

      1. Cool! I do not consider this rich red to be a cop out because it is a dinnerplate dahlia, which, for me, would be as wild and crazy as purple. I mean that, although the color is not too unusual for me, the size is.
        You know, I learned to drive with a 1977 Electra that was a similar color. The color was elegant, but . . . there was a lot of it. I mean, perhaps, rich colors are better for smaller cars.

      2. My first car was banana yellow (it was actually called ‘Broom Yellow’) so I guess there’s something to be said for small cars and rich colours – they need to be noticed on the road! 🙂

      3. hmmm, . . . Have you seen the bumper sticker that reads, “My other car is a broom.”?
        Anyway, I think that smaller cars more commonly get bright colors because they ‘can’. I mean, they are not so obtrusive. For larger cars, such colors are excessive in large quantities. I am not at all proficient with colors (obviously), so I do not know. I just notice that rich colors like burgundy red, which looks good on a Skylark, can look garish on and Electra.

    2. Johnnie Ellis is a very lovely white cactus, isn’t he?! I’m so glad such a beauty is named after my husband. I doubt he will ever be available overseas so not sure how you will get him……

      If you want to try a non-white cultivar, may I suggest ‘Christopher Taylor’ ? It’s a beautiful red, water-lily flower with long chocolate/purple stems – it’s a stunner!

      1. WHAT?!?!?! I was hesitant to ask about that! Oh well, now I know. I sort of suspected that the ‘Johnnie Ellis’ dahlia could not be sent to America.
        Oh cuss!
        ‘Siberia’ is commonly available, but would be no fun without ‘Johnnie Ellis’. Heck, that would be one of those cheap and common ‘big box’ purchases that I am none too keen on. I could sort of justify it in conjunction with something more . . . justifiable. Well, I will adapt, and just may get ‘Siberia’ anyway. I really do like it.
        ‘Christopher Taylor’ was already a consideration for purchase from a local nursery. Not only is it commonly available, but I happen to be quite fond of it. My first dahlia, which I found on a compost pile in Montara when I was in high school, looked exactly like it. Seriously, modern pictures of ‘Christopher Taylor’ look just like that old dahlia. Anyway, my primary objection to ‘Christopher Taylor’ is that, since I am already so fond of it, there is not too much of a challenge to selecting it for the garden. I mean, it could be sort of a cop out. If I am to engage this challenge, I may as well do it properly and weirdly, and select a color or colors that I have major difficulty with. Heck, I could try something with purple! (GASP!) Although my garden and the color within it will always be simple and bland, as I prefer it to be, it is healthy to try something crazy once in a while. Thank you for your recommendation; but this is something that I should do on my own. I will brag to you later about it.

      2. We had ‘Siberia’ a couple of years ago. A lovely white dahlia, although, personally I felt the blooms were a bit too ‘green’ for me…..I am not a fan of a green flower – it’s just not right! 😉

      3. OH! Well, that is good to know! I believed that it was as white as it looks in pictures. Although green flowers might be a hit today (Saint Patrick’s Day) they really are . . . weird. Dyed carnations have good color at least. Most other green flowers look rather sickly. My objection with green in white flowers is that such flowers are supposed to be ‘white’! I have seen excellent white dahlias before, but I do not get names. I believe that I have seen ‘Spartacus’ also, but of course, did not get the name.

  4. For the last 3 years I have had zero luck overwintering my tubers. The first winter I dug them up,cleaned them off,let them dry and put them in a crate to open air in my basement. Not one came up when I planted them. Next year I tried what floret flowers said they did. I prepare as usual,once dry I wrapped them lightly in plastic wrap. Put them in a box in my basement closet. When I opened them,they were either mushy mold or dried and desiccated. Ok,third winter,prepped as usual,stored in paperbags near the heated wall of the garage. I had like 300 tubers. 95% were dry husks on outside but the insides were mush when I opened the bags last week. I am planting the very dried up ones to see if they live. I am just so frustrated with spending money on these every year to see them get ruined over the winter. Truly, do you have any suggestions for next autumn?

    1. Hello Michelle, I would never, ever wrap in plastic wrap. The tubers will not be able to breathe and will rot off. They should be stored in old soil or straw somewhere cool and dark over the winter. They need air circulation in a cool and dark environment while dormant. You could also just leave them in their pots, let the soil completely dry out (again, put them somewhere cool and dark for the winter) and revive them in the spring but repotting and putting somewhere light and warm. I hope this helps.

  5. Great post, and very timely as I’m trying dahlias for the first time – bought 3 ‘Fancy Pants’ tubers from a reputable provider and have just planted them in plastic grape containers to start them off in home-made compost. I’ve moistened the soil and won’t add more water until I see growth. Do they need heat and sun, or cool and shade at the moment? My potting shed is more like a greenhouse with twin-walled polycarbonate sheets on roof and three sides – south facing – but temperature drops over-night. I have a shadier greenhouse if necessary. I intend to grow them in pots and place those in the greenhouse overwinter perhaps covered with garden fleece or under upturned cardboard boxes? Any suggestions please?

    1. They will need warmth and light to enable strong growth. They will be fine in your potting shed as long as they temperature doesn’t drop – I’d say any lower that 5 degrees and I would bring them inside overnight. However, to get them going, the greenhouse may be a better option especially if it’s warmer. If you store overwinter, don’t store them in the greenhouse as they need a cool, dark place. A greenhouse would be too warm and light in the winter, in my opinion. We put ours in old soil or straw, in boxes in the garage under the potting bench. Putting them in cardboard boxes with fleece over them would be fine but I would be tempted to put straw between them too. I hope this helps….

  6. that was really helpful, thank you. i am trying them for the first time this year! just 4 tubers to begin with. i can’t believe you got all those big beautiful dahlias in the shed bed from those tiny little plants…

    1. Gill, you won’t believe the growth that goes on with dahlias when they’re healthy, happy and being properly cared for. Incredible. Good luck with your 4 – let us know how they get on – which varieties are you growing?

    1. Use a pot that is a little bigger than the tuber you’re planting. Use a good quality growing medium, for example John Innes No.2, dress the top of the soil with horticultural grit and place outside (once all danger of frost has passed) in a light and sunny location. Water regularly and feed once the plant is producing flowers – do you have any specific ‘growing in pots’ questions, Tracy? Hopefully the above is helpful…..

      1. Thank you Tracy. That’s dahlia ‘Spartacus’ which is a particular favourite

  7. A great deal of information and so well structured – even I can understand the instructions. (However, don’t watch this space… ). due to all the song and dance from ‘The Frustrated Gardeners’ I succumbed to beauty and have invested in a dozen dahlia tubers. Unfortunately, my garden is low, clay and distinctly soggy. So I’ve bought a lot of enormous pots and filled them with upside down plant pots (cheap drainage) and John Innes no 2 compost mixed wth vermiculite to ensure the roots stay moist even on very hot days.
    My question is: I’m tiny, old and feeble…. (But gardening is an addiction for me!) I can’t see me being able to take these heavy pots inside for the winter…. Do you think if I wrapped a few layers of bubble wrap around all the pots (they will be arranged together for effect.) this would protect the tubers from frost? I could cover the tops with a couple of layers of fleece too if you think that may be needed here in the midlands?
    Or, should I dig out the tubers to bring into the garage over winter??? Thank you very much for any advice you may give. Don’t worry, I won’t hold it against you if the fleece &/or bubble wrap blows away, It is just an idea to save a little of my energy!!!!

    1. Hello Myra, I think your best bet is to lift the tubers from the pots, store them in the garage somewhere cool and dark for the winter (in old soil/straw in cardboard boxes or mesh trays for air circulation) and then replant in the Spring. Alternatively, you could wrap the pots with fleece – I wouldn’t use bubble-wrap as there would be no air circulation and the tubers may well rot off – you could then refresh the top few inches of soil in the spring and give them a good feed once they start flowering….. I hope this helps you 🙂

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