Dahlia plant in pots

Can Dahlias Be Grown In Containers: Learn How To Grow Dahlias In Containers

Dahlias are beautiful, full-blooming natives of Mexico that can be grown virtually anywhere in the summer. Planting dahlias in containers is a great choice for people who have little space for a garden. Even if you have a garden, a container grown dahlia can live on your patio or front porch, bringing those gorgeous blossoms up close and personal. Keep reading to learn how to grow dahlias in containers.

Can Dahlias Be Grown in Containers?

Can dahlias be grown in containers? Yes, but it’s a little bit of a process. If you want a bulb you can plant and forget, you may want to pick a different plant.

Choose a container that’s big enough in diameter that the tuber can fit comfortably when laid horizontally in the bottom. Just-planted dahlias tubers are at risk of rotting, so make sure your container has plenty of drainage. If it only has one or two holes, consider drilling a couple more.

Moisten a very loose potting mix that contains good draining elements like perlite and bark, and fill the container about a third of the way up. Lay your tuber flat in the container with the eye or sprout, if there is one, facing upwards. Add more potting mix until the tuber is just barely covered and the eye is just sticking out.

Care for dahlias in pots includes giving them support as they grow taller. Next to the tuber, sink a strong pole up to five feet in length to the bottom of the pot. Drill two holes into the side of the pot opposite the pole, and anchor it in place with a piece of wire or string. Placing the support pole at this stage saves the roots from being damaged in the future.

Planting dahlias in containers requires some maintenance at this stage. If you’ve started it inside, which is recommended in areas with short growing seasons, put your container grown dahlia directly under a grow light set to a 12 hour timer.

Keep track of the plant as it grows, and lightly fill in more potting mix around it as it grows up. Keep doing this until you reach one inch below the top of the container.

How to Grow Dahlias in Containers

Care for dahlias in pots, once you’ve filled the container with potting mix, is not too hard. Place them outside when the weather warms in a place that receives full sun and water and fertilize them regularly.

As your container grown dahlia gets taller, tie it to the stake and pinch off the top to encourage bushy growth to the sides.

How to grow Dahlias

Blousy dahlias make wonderful cut flowers
Image:

Dahlias are enjoying something of a renaissance at the moment, and it’s easy to see why. They come in many shapes and colours: from showy, double-form dahlias that look wonderful in a vase, to simpler, single-flowered varieties, which attract lots of bees. Dahlias are also easy to grow, giving you late-summer colour when many other plants are past their best.
Whether you want beautiful cutting blooms, or fabulous flowers to bring your patio containers to life, there’s a dahlia for every purpose and taste. Read our guide to learn how to grow dahlias in your garden.

Where to grow dahlias

Dahlias love full sun and rich, fertile soil
Image: Syda Productions

Dahlias do best in rich, fertile, well-drained soil and full sun. They’re heavy feeders, so dig in plenty of well-rotted manure or compost before planting, and top-dress with a general-purpose fertiliser.

Seeds, tubers or potted plants?

Plant dwarf varieties 12″ apart
Image: Peter Turner Photography

Dahlias can be grown directly from seed or dormant Dahlia tubers, or grown in pots to be planted out once they’re established. If you’re growing dahlias from seed, sow them between February and April. If you’re growing from tubers, plant them from April to May. Plant out potted dahlias in May and June when there’s no risk of frost.
When it comes to spacing your dahlias, plant taller varieties, like ‘Badger Twinkle’, about 60cm (24″) apart; medium sized varieties, such as ‘Candy Eyes’, 45cm (18″) apart; and dwarf bedding varieties 30cm (12″) apart.

How to grow dahlias from tubers

Plant out potted dahlias in late-May or June
Image: Luisa Fumi

Plant dahlia tubers directly into the ground from around mid-April. Don’t worry about frosts, as the soil will insulate the tubers.
Prepare a planting hole that is 10-15cm (4-6″) deep, and wide enough to accommodate the dahlia tuber comfortably. Place the dahlia tuber inside with the ‘eye’ (where the tubers meet ? often with remnants of last year’s stems) facing upwards. Backfill with the remaining soil, gently firming as you go, and water the tubers in thoroughly.
You can also pot up your dahlia tubers in April and grow them on in a greenhouse to give them a head-start; planting them out after all risk of frost has passed.

Growing dahlias in containers

Dahlias make great container plants
Image: Krystian Duzynski

Growing dahlias in pots is a great way to brighten up your patio. Choose a container which is at least 30cm (12″) in diameter and depth for best results. Remember, dahlias enjoy a rich, fertile soil, so use multi-purpose compost and add a slow-release fertiliser for strong growth. Plant your tubers 10cm deep ? as you would when planting them into the ground.

Frost protection

Make sure your dahlias are protected from more severe weather
Image: Berschauer Joachim

Dahlias are half-hardy so they will need protection from frosts. Pot-grown plants should only be planted out after all risk of frost has passed in late May or June. Alternatively, leave your dahlias in the greenhouse all year round. If you planted dahlias in the ground and their shoots emerge while there’s still the risk of frost, cover them with horticultural fleece for protection.

Staking dahlias

Stake tall dahlias to prevent them from flopping over
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Tall dahlias are prone to flopping over and are easily damaged by the wind. You can prevent this from happening by staking them. Stake dahlias as you plant them because it’s easy to pierce the tubers once they are hidden underground. Use bamboo canes or twiggy sticks for a more natural look. Alternatively, use garden obelisks to support your growing dahlias, placing the obelisk directly over the plant.
The supports may look untidy initially, but your dahlias will soon grow to cover them. When you’re tying in your dahlias, make a figure of eight with the string to prevent the stems rubbing against the canes.

Summer care

Pinching out dahlias encourages more flowers to grow
Image: Flagman 1

Pinching out

Pinching out dahlias once they reach 40cm (16″) tall encourages branching and more flowers. Simply pinch off the growing shoot just above a set of leaves. Dahlias can be pinched again once side shoots develop. For giant blooms however, it’s best to only allow three to five flower stems to develop.

Feeding

Once flowers appear on your dahlia plants, feed with a high-potash liquid fertiliser, such as tomato feed, every two weeks until early September. Feeding dahlias will encourage more flowers.

Deadheading

Deadhead dahlia flowers as they fade to encourage more blooms to grow. Simply pinch or cut the flower stem back to a pair of leaves to keep the plant looking tidy.

Lifting dahlia tubers for the winter

Look after your dahlias through the winter and they’ll reward you next summer
Image: Cris D

If you live in a mild climate, you can leave dahlia tubers in the ground all year round, just make sure your soil is well-drained. If your garden suffers from frost, you’ll need to lift dahlia tubers with a garden fork once the first cold snap has blackened their foliage. If leaving dahlia tubers in the ground, cover them with a 10-15cm (4-6″) layer of bark chips or compost.
Once lifted, clean the tubers and trim off any fine roots. Cut the stems down to 15-20cm (6-8″). Place the tubers upside down for few weeks to dry off completely. When they’re dry, put your tubers into boxes or trays of dry sand, peat-free compost, vermiculite, or coir fibre and store in a cool but frost-free place.
It’s a good idea to check your dahlia tubers regularly throughout the winter to look for signs of mildew or rotting. Cut out any affected areas with a clean sharp knife.
For more help growing these beautiful, versatile flowers, check out our short how-to video:

This morning I woke up, put the kettle on and wandered outside to see if the milk had been delivered, which means going down the garden path. As I tried not to slip on the frosty flags, I felt the presence of something in the sky behind me, turned and saw a peregrine falcon flying over the house, beating bent-backed scimitar wings in that idiosyncratic muscular, direct manner. If you know anything at all about birds there are certain rules that always apply. One of them is that if there is any doubt then it isn’t. When you see the real thing you know. If you are unsure whether it is a buzzard or golden eagle then it is always a buzzard. So it is, in this part of the world at least, with peregrines. You see them with a thump of shocking recognition. So, for a breathless minute, one of the fiercest and most feral of creatures on the planet beat straight above my primped garden and, until it had disappeared into a dancing mote in my eye, we alone shared the tentative dawn sky, the carefully edged path, the clipped yews, the family sleeping indoors, the everything known and unknown of that minute. Then it is gone and with the pang of loss a great flush of experience and excitement that lights up the rest of the day on into memory, and, if you have any shred of wonder about you, for the rest of your life. The milk, by the way, had not arrived.

Now, back to business. Part three of my bulbous mini-series. Having wended through snowdrops, daffodils, tulips, alliums, lilies, crocosmia, et al, we arrive, panting a little, at autumn and, crucially, dahlias.

I have written before on these pages on how dahlias were locked into my mindset as cut flowers of the Fifties, grown by my mother in a border down by the chicken run dedicated year on year to them and gladioli, the combination looking in full flower like a tea cosy knitted from all the scraps of wool left over from Christmas-present jumpers. I could not accommodate this in any kind of reality and did not grow either for 30-odd years, but having exorcised my demons with flowers I am back in love with dahlias and glads and would not be without them.

Dahlias are tubers – and like potatoes were originally imported from their native Mexico as potential food – and do best in a rich soil with plenty of added organic material so the tubers can swell. As with all bulbous plants, the bigger the bulb, corm, tuber or rhizome, the better the flowers are likely to be. They are best planted reasonably deep, although if they are to be lifted then 6-9in is deep enough. If they are to be permanent then double that.

Dahlias are not hardy and the first proper frost will reduce the flowers and foliage to blackened rags, but it is a mistake to lift them before the first frost as the tubers go on growing and swelling right up to that frozen moment. But if you are likely to get any sustained frost below -5C, or any late-spring frosts – and that includes me and most people north of Oxford – then it is best to dig the tubers up, dry them and then store them in damp, used potting compost in a frost-free dark place. Replant them in April, mulching them well. By the time the new growth works through the layers of soil and mulch, the frosts should have passed and the roots will be working well into the soil. If you want late flowers, cut the initial new growth back in early June to 12in or less, and they will flower all the better for it in September and October.

Like dahlias, gladioli can come in a range of Fifties’ lipstick pinks, pastel yellows, mauves, lilacs, oranges and other hues of that ilk. But it is wrong to brand them with that palette because there are wonderful rich colours, too, especially in the species gladioli (of which there are nearly 200) like Gladiolus byzantinus, G cardinalis, the white with deep interior markings of G callianthus and some of the florists’ varieties like ‘Firestorm’, ‘Fidelio’, ‘Black Beauty’, or the green ‘Spring Green’ which exactly fits what my American friends would call ‘chartroose’. Most are tender and are best dug up each winter along with the dahlias. But unlike dahlias, which, especially if deadheaded regularly, should flower from August to November, gladioli only flower for a couple of weeks so it is a good idea to plant a handful of the (surprisingly small) corms every couple of weeks from Easter to Whitsun to maintain succession of flower.

More recognisable as ‘bulbs’ are the autumn crocus and colchicums that start to appear from September. Colchicums look like crocus but are members of the lily family. Autumn crocus look a bit like colchicums but are members of the iris family. Confused? Stay with it. The easiest way to distinguish them is to count the stamens: colchicums have six whereas crocus have only three. Autumn crocus are smaller and neater than colchicums, growing to 2-4in, and many of them have very narrow, grass-like leaves that appear at the same time as the flowers. All colchicums are naked, but in a baby birdish, toadstoolish sort of way rather than lovely and nude. They do have leaves – good ones with a spread of up to 18in – but they do not appear at the same time as the flowers, appearing in spring and dying back in summer before the flowers appear in September.

Grown in grass its nakedness is hidden and, perhaps more importantly, supported. Colchicums grown in bare soil beneath a tree or shrub are easily and irretrievably bashed by wind and rain. Although the grassland can be damp in winter, it must be dry in summer while the corms are dormant and as open to full sun as possible, although they are often found in woodland so perhaps some dappled shade suits them well so long as it is dry. They should also be planted deep – with at least 4in of soil over the top of them.

Most autumn crocus are suitable for a container or rockery where they can be seen as miniature, jewel-like flowers, but some can be grown against a larger canvas. Crocus speciosus, and C nudiflorus, are the easiest to naturalise and fit in well with a basic haymaking regime – namely grass that is left long until midsummer, cut and raked, cut again at the end of August just before the crocus appear so the flowers will stand proud of the grass, and then cut back again in autumn.

The only frost-hardy nerine is Nerine bowdenii and it is glamorous, long-lasting, and … well, to my eye at least, without charm. It is the pink I think. But should you wish to grow them for their undoubtedly dramatic and long-lasting autumnal display, the bulbs should be planted very shallowly although, in cold areas at least, just covered by soil. They need a really good summer baking to flower, so the base of a south-facing wall or in pots left in full sun would be ideal. If they stop flowering, dig them up, tease the bulbs apart and replant with some space between them.

Growing dahlias in pots

I am mad keen on dahlias, everybody knows that. One of the things I’ve been experimenting with this year is growing dahlias in pots, trying to find slightly compact varieties because dahlias can grow extremely tall and obviously that wouldn’t be good in a pot.

There’s a new generation of dahlias and this one is part of them. It’s called Dahlia Hot Cakes and it’s what’s called an anemone-flowered dahlia and you can see what that’s referring to, but it’s so brilliant in a pot because it’s got these big, really wonderful saucer flowers which give you such impact over this kind of scale and yet it isn’t too tall. This example isn’t staked at all, it is just one tuber in a pot looking fabulous – plant this dahlia and you’re onto an absolute winner.

This is the next one which is called ‘Roxy’ – an absolute classic for pots and again you can see how perfect it is. The scale’s really good, it’s got this lovely healthy foliage which contrasts so brilliantly with the colours of the flowers, and that’s what you want for a good container plant that is not just about flowers. It’s about foliage and the flower, and the contrast and balance between them.

Then, there’s another and the final one on trial this year is this, which is my absolute favourite, called ‘Totally Tangerine’. Another anemone-flowered variety which has been in flower already for a month which is substantially early as they’re all coming into flower in the garden at the moment. But this has been in flower since the middle of June and last year it flowered right the way through until the middle of December – what a result. Here we’ve got two tubers planted with Calendula officinalis ‘Indian prince’ and Antirrhinum ‘Liberty Crimson’ and this beautiful grass which is called Panicum Elegans ‘Frosted Explosion’ which is like a great explosion. It’s not in flower yet but the main point of this pot is this dahlia, it is just completely sensational.

Tips for growing dahlias:

  1. They’re quite hungry so you want a rich compost.
  2. They are thirsty. We are watering this pot (Totally Tangerine) every day, which sounds a lot, but it’s been a dry summer
  3. If you grow a taller variety you’ll need to stake them. The beauty of this pot (Totally Tangerine) is you don’t need to stake them.
  4. Finally, either pick or deadhead them down to a leaf to promote more flower formation.

Happy gardening,

Sarah

Related articles and videos:

  • Planting up your dahlia tubers
  • How to grow dahlias
  • Understanding dahlia groups
  • When to plant dahlias

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