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.
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.
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.
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.
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.
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!
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!
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!
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!