Fancy filling your garden with flamboyant and flouncy flowers? Then you need to learn how to grow dahlias in pots, stat!
Famed for their dramatic beauty, planting dahlia tubers usually winds up on every gardener’s list of must-try garden ideas at least once (at least), and for good reason: They bloom straight through summer and well into the autumn.
And this means, yes, that they’re the perfect flower to work into your container garden ideas, adding a much-needed pop of colour in the duller months of September and October.
Worried you don’t have enough room in your garden borders for dahlias? Don’t be: they can absolutely flourish in containers, provided the pots are large enough.
‘Dahlias are perfect for most gardens and homes due to their versatile nature,’ promises Dani Turner, customer experience director at family-run florist Bunches.
Still, while there are many different dahlia varieties to choose from, Dani suggests you look for one ‘that is slightly smaller and compact’ if you’re sussing out how to grow dahlias in pots, as ‘some can grow as tall as 5ft.’
Keen to get started? We spoke to the experts (and drew upon our own experience with garden trends) to figure out everything you need to start growing dahlias in pots and containers.
You’re welcome!
What you’ll need
Before you start reading up on how to grow dahlias in pots, it’s a good idea to gather all of the equipment you will need first.
How to grow dahlias in pots
1. Choose the right container
‘For Dahlias that are going to be grown in a pot, it is best to choose one that is at least 30cm in diameter and 40cm deep,’ Dani recommends.
Gardening expert Fiona Jenkins at Myjobquote.co.uk echoes this sentiment. ‘For most dahlia varieties, you want to choose a fairly large pot; a 12 – 14 inch (30 – 35cm) diameter pot is ideal, and 12 inches of depth is perfect.’
Because they, ‘put on a lot of top growth, a fairly heavy pot is required to counter-balance all the top foliage, otherwise, they will blow over,’ says Angela Slater, Gardening Expert at Hayes Garden World.
She recommends a heavy terracotta or glazed clay pot. You may also need to stake your dahlias as they grow to prevent them from falling over.
Once you’ve sourced all of the equipment you need, you can get to work planting your dahlias up in pots.
Here’s what you need to do.
2. Fill the pot with the right soil
Graham Smith MCIHort, a gardening expert from LBS Horticulture, advises that getting the right mix will ensure your dahlias thrive.
‘Fill the pot with multipurpose compost (pick up a bag of Growmoor on Amazon), and mix this with organic matter,’ suggests Graham. ‘You can also add slow-release plant food (this Vitax Dahlia feed from Amazon should do the trick) at the same time.’
3. Wait for the right time
Dahlia tubers can be started into growth in March or April in pots undercover, as this will give them the optimal conditions to develop and grow, compared to when a sudden frost could hinder their growth or potentially kill the plant entirely.
‘To plant, mound a few inches of potting soil at the bottom of the pot while forming a little bit of a hill. Balance the tuber on the mound and then carefully fill in around the tuber with your potting soil,’ Fiona instructs.
‘Press and firm it around the tuber gently as you go along.’
‘Dahlia tubers should be planted at the same depth as they were in their original pot,’ adds Graham.
You can plant them out in the garden in late May and June.
4. Find them a sunny spot
‘Dahlias are sun-loving plants that require at least 6-8 hours of direct sunlight each day to thrive,’ suggests Jason.
‘Place your pots in a sunny spot on your patio, balcony, or in your garden. Ensuring that they receive adequate sunlight will encourage strong growth and abundant blooms.’
In particularly scorching summer weather, you can move your potted dahlias into the shade to give them some respite but they do prefer sunny conditions.
5. Add manure
Dahlias are not fussy and will grow in any fertile, moist, but well-drained soil.
‘To enrich the soil and help them grow, you can add organic matter, such as manure, to give the soil more nutrients,’ suggests Dani.
6. Pinch out the tips
Graham Smith, a gardening expert from LBS Horticulture, advises pinching out dahlias for even more blooms.
‘Once the dahlias are 20cm tall, pinch out the main growing tip to encourage more flowers,’ explains Graham. ‘The main growing shoot is often in the centre of the plant and growing upright, and this should be cut down to the top pair of leaves.’
‘Once your dahlia has at least four sets of leaves, you can ‘pinch’ away about 8cm from the top of the central stem, which will encourage the plant to direct its energy into producing more side shoots,’ explains Lucie Bradley, gardening and greenhouse expert at Easy Garden Irrigation.
‘To prevent any damage during this process, ideally use a sharp, clean pair of snips rather than your fingers so you get a clean cut rather than a stretched or squashed stem,’ she adds.
These Darlac ergo gardening snips from Amazon should do the trick.
7. Fertilise regularly
Dahlias are ‘greedy feeders,’ according to Angela, so they ‘need a constant supply of nutrients.’
‘Once every fortnight, you can provide a high potash feed to the dahlias, such as tomato feed (try Doff Tomato feed from Amazon), as this will keep the plants flowering well,’ explains Graham.
Once your dahlia plants begin to flower, you need to regularly provide them with fertiliser to help them maintain a healthy foliage throughout the growing season. ‘Use a balanced, water-soluble fertiliser that is suitable for flowering plants,’ affirms Jason.
‘Dead-heading or picking the blooms is essential to keep the plant flowering as long as possible,’ proffers Angela.
7. Water wisely
As you may expect, you will need to water your dahlias for them to thrive. ‘While they do require consistent moisture, it’s important to avoid overwatering, as this can lead to tuber rot,’ reveals Jason.
‘Check the soil moisture regularly by inserting your finger into the potting mix. Water the plants when the top inch of soil feels dry to the touch.’
‘Water the plants well weekly,’ adds Graham. ‘And tie a stake to any new growth every week (unless you are growing a dwarf variety).’
You’ll also want to ensure that the pot or container that you’ve chosen has good drainage to prevent the soil from becoming waterlogged, which can also be detrimental to the plants.
8. Watch out for pests
Aphids can be a problem for dahlias, but, ‘they can be controlled by rubbing off between finger and thumb or by feeding the birds who will dispose of them for you,’ says Angela.
‘Earwigs can also be a problem but can be controlled by placing an upturned pot stuffed with straw on top of a cane.’ Keep an eye on your beautiful blooms so that you can immediately see if you have any pest problems and deal with them before too much damage is done.
9. And don’t forget to deadhead
We’ve said it before, and we’ll say it again: If you’re going to learn how to grow dahlias in pots, you also need to learn how to deadhead dahlias so they flower beautifully all autumn long.
‘Keep it trimmed down, and keep removing the wilted flowers, and you will have a neat bushy plant,’ says Christopher O’Donoghue, one of the co-directors at Gardens Revived.
‘Dahlia buds are round in appearance, whereas faded flowerheads will be more pointed, and you should remove the whole flowering stem,’ adds Graham.
Sounds easy enough, right? Next up: learning how to grow peonies in pots (if you fancy something a little more advanced, that is!).
FAQs
Should I soak dahlia tubers before planting?
‘If you are aiming to grow dahlias early in pots, such as March or early April, soak the tubers in a bucket of lukewarm water for an hour to rehydrate them,’ explains Graham Smith, gardening expert at LBS Horticulture. ‘
After this, plant the tubers in a pot, ensuring that the joint where the roots and stem meet is facing upwards.’
‘Although not absolutely necessary when planting dahlias, I would always recommend soaking the tubers for up to one hour in water that is room temperature prior to planting as it enables two things to occur,’ suggests Lucie Bradley, gardening and greenhouse expert at Easy Garden Irrigation.
‘Firstly, it removes any dirt or debris which is surrounding the tubers, making it easy for you to spot if there is any problem with them, so you can spot and remove any diseased parts prior to planting to prevent it spreading to the whole tuber.’
‘Secondly, an hour in water will rehydrate potentially dry, shrivelled tubers, giving them an energy boost so that they will start growing sooner than those which haven’t been soaked.’
‘As you need to be careful with dahlia tubers that they don’t rot, once they have finished soaking and any damaged parts are removed, remove any excess moisture by patting the tubers on a paper towel,’ adds Lucie.
How many dahlia tubers per pot?
‘You should plant each dahlia tuber individually in its own pot,’ says Graham Smith, LBS Horticulture’s gardening expert. ‘This will prevent overcrowding as the plants grow, as some varieties of dahlia will require and take up a lot of space.’
Although there are over 57,000 varieties of dahlias to choose from, including the dainty pompon dahlias with heads as small as 5cm through to exuberant dinner plate dahlias with blooms over 35cm wide, I would usually plant one dahlia tuber per pot,’ agrees Lucie Bradley, gardening and greenhouse expert from Easy Garden Irrigation.
‘For healthy growth and so they produce beautiful blooms, you would normally allow at least 30cm between plants, which means one tuber per pot.’
‘This allows these greedy plants to produce a large enough root structure to gather up all the nutrients they need and also enables good air circulation around the plant to prevent diseases caused by excessive dampness, such as powdery mildew.’
What are the best dahlias for growing in pots?
You’ll want to choose a variety of dahlia that is suitable for container gardening.
As ‘some dahlia plants can grow quite large, it’s best to opt for dwarf or compact varieties,’ says award-winning garden designer Jason Williams, also known as The Cloud Gardener.
‘These smaller plants are well-suited to container growth, maintaining a more manageable size while still producing an abundance of beautiful blooms.’
What should I do with my potted dahlia in the winter months?
The added benefit of growing your dahlias in a pot or container is the fact that you can easily move them, either if or when you move home or during the less hospitable colder months.
Dani reveals, ‘although dahlias are usually bought annually, they can be kept alive during the winter months.’
‘To do this, after the first frost has killed the foliage, bring the potted dahlias inside to a cool, dry and darkened place – a basement or a garage would be perfect for this.’
‘They don’t need much water during the winter but just keep checking on them to make sure they aren’t too wet or are in need of some water to rehydrate them,’ she concludes.
So there you have it: how to grow dahlias in pots and keep them blooming all the way into autumn.
And if you’re keen on getting more expert tips, check out Monty Don’s top tip for growing dahlias and keeping them in bloom to boot.
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