Dahlias in Pots: Grow Stunning Dahlias With These 10 Simple Steps
If you want to grow large, beautiful dahlias in pots, this is the guide for you
By Hannah Miller at DIY Gardening
Dahlias are my favourite garden plant, and for good reason, I love the huge colourful blooms that burst into life late in summer and early autumn, just when my hydrangeas and other shrubs start to fade.
They work well in the back of borders where they tower majestically over my hardy geraniums, coneflowers and other smaller plants.
But can dahlias be grown in pots?
Yes, they can, and on this page, I’ll show you exactly how and what to watch out for.
Below are just two examples of our dahlias in pots:
Step 1: Choose the Right Dahlia, a Suitable Pot and Supports
There are thousands of varieties of dahlias, and while most can be grown in pots, the dwarf or smaller varieties perform better and are easier to care for.
Consider these examples:
Dwarf dahlias grow up to 2 feet tall and are perfect for the front of borders and small/medium-sized pots.
Medium height dahlias grow up to 4 or 4.5 feet tall and require a heavier, larger pot and generally need light staking.
Tall dahlia varieties grow up to 6 feet tall and require secure staking or a frame for support and also a large, heavy container at the base to prevent the plant from tipping over.
For dwarf and medium-sized dahlias, pot sizes from 12-15″ (30-40cm) are best.
Use 45cm/18″+ pots for only the tallest of dahlias or when you want to grow more than one dahlia in the pot.
Containers that are wider at the bottom offer more stability and are ideal for top-heavy plants such as dahlias.
Not sure which type of support to use? We use 5ft metal stakes that are coated in green plastic. They last for years, are discreet, never bend and are easy to tie the stems to.
Step 2: Inspect the Eye
Dahlia tubers have small eyes at one end that sprout stems.
If there’s no eye on the tuber, it can’t sprout.
It’s not always easy to locate the eyes, so if you can’t find them, plant the tubers shallowly in small plastic pots and keep an eye on them, there’s no point planting a dud in your best pots. You can always pot-on dahlias as they transplant well when young.
It’s normal for the tubers to look a little shrivelled but if there are signs of rot or the tuber is very soft and squidgy, it’s probably not going to grow a sprout.
Step 3: Store The Dahlias Until They’re Ready For Planting in Pots
Dahlia tubers are susceptible to frost and will need to be kept in a protected environment until the time is right to plant them outside, ideally, after the risk of any frost has passed.
Depending on when you purchased the dahlias and how they were packaged, you may need to transfer them to a cardboard box filled with dryish compost, leaving just the trimmed stem and crown above the surface. Then locate them in a cool, dark spot such as a garage or other outbuilding.
Ventilation is also important as the tuber could rot if it’s kept in a damp location. Cut a few holes in the side of the box and raise it off the ground slightly, and the tubers should be fine.
Step 4: Give The Dahlias a Headstart
If you live in the south of the UK or the United States, you can plant dahlia tubers straight into your large pots or containers as soon as the risk of frost has passed, but anyone living in cooler climes should start them off in smaller plastic pots and protect them by either keeping them in a greenhouse or bringing them indoors or into a shed/garage overnight.
The dahlias can be transplanted to either a border or their final pot once the risk of frost has passed; this is a great way to give dahlias a headstart and to check which ones are sprouting as not all will.
You don’t need to use large pots; small plastic ones will suffice as they’ll only be holding the dahlias for a month or two.
Just squeeze the tuber into a plastic pot with the eye pointing upwards and fill with compost until there’s no more than 1cm of compost above the tuber, leave the old stem just above the soil level.
Keep the compost moist but not soggy and locate it in a bright spot.
Step 5: How to Choose The Best Location For Dahlias in Pots
Whether grown in pots or borders, all dahlias require at least 6 hours of sunlight and ideally more than 8 hours, so choose a very bright spot, away from shade.
Compost and soil in pots (especially small pots) will dry out quickly during hot spells, so watering is essential. Hence, pots and containers should ideally be larger and located nearer to the house or a garden tap for ease of watering.
Dahlias that are located near walls or other taller shrubs tend to lean as they grow towards the sunlight, and this needs to be corrected with stakes or support frames; otherwise, the stems may break under the weight of the heavy blooms. Dahlias look at their best when they grow vertical and upright.
The best location for a potted dahlia is, therefore:
- In a bright spot with light on all sides (i.e. at the end of a patio).
- Near a water source, the gardener will need to water the dahlia several times a week and daily in heatwave conditions.
- The pot should be elevated on feet and have holes in the base as dahlias hate wet feet.
- In a spot where the dahlia has some space, so it doesn’t have to compete with other plants for light.
Step 6: Disease and Pest Control
The National Dahlia Society has published a list of all the diseases and pests that affect dahlias, but the most common is slugs, snails and caterpillars, which can cause damage throughout the growing season but are particularly problematic when the dahlia leaves are young and tender.
Most gardeners find it fairly easy to protect plants in pots from slugs, while borders are a different matter altogether as the slugs have more places to hide.
Once the dahlias have matured and grown in height, and the temperature outside is higher, slugs are less of a problem, but issues can arise again in autumn when the ground becomes wetter.
Slug damage to a young dahlia. If left unchecked they will devour all the leaves and weaken or kill the plant.
Step 7: Initial Pinching Out
Dahlias look best when the plant is bushy with lots of blooms, but to achieve this, the gardener needs to pinch out the centre stem as this encourages further shoots, which will produce more blooms later in the season.
This step will set the dahlia’s growth back a few weeks, but the reward is worth waiting for.
The initial pinching out is easy – when the dahlia has four sets of leaves (when it’s roughly a foot tall), pinch out the centre stem or cut it off using a set of secateurs.
Step 8: Fertiliser and Water For Dahlias in Pots
Dahlias are both thirsty and hungry plants that require more feed and water than most perennials, especially if grown in pots.
Watering requirements – dahlias should be grown in moist but not waterlogged soil, and if placed in a pot, you may need to water them several times a week or even daily during heatwaves.
Fertiliser requirements – dahlias are hungry plants that prefer a balanced fertiliser that promotes stem and leaf growth during the spring and early summer. From mid-summer onwards, the gardener can switch to a low nitrogen feed with higher levels of potash and potassium, as this will encourage large blooms to form. Liquid fertilisers can be fed every week or 10 days, while slow-release pellets and granules can be applied every 6-8 weeks, depending on the content and how quickly the nutrients are released.
If you’re looking for a good all-round feed for dahlias, fish, blood and bone is very good and popular among gardeners.
If you want to grow huge blooms that really stand out and grab attention, our guide to the best dahlia feed is a must-read.
Fish, blood and bone – perfect for dahlias
Step 9: Ongoing Pruning and Deadheading
Deadheading is a great way to divert energy to new blooms, so for best results, remove any dead flowers as soon as you can. You’ll see more and bigger blooms by deadheading, and it improves the dahlias appearance.
Selective pruning will determine whether your dahlia grows huge flowers that are fewer in number or more numerous blooms that are smaller.
Many dahlias become top-heavy with the weight of several blooms on one stem, either bending or snapping it, so selective pruning not only determines the size and number of blooms but also protects the plant from damage.
For more blooms that are smaller in number – pinch out or cut off the centre stems when you see buds forming on side stems.
For huge blooms that are fewer in number – cut off the side stems when buds form, leaving a single central bud on each stem.
Selective dahlia pruning is generally done when buds have formed but are still small and haven’t grown into full blooms, so you can easily see where the flowers will grow. Cut off the stems before you see any buds, and none may form at all.
(Our blog contains a very helpful guide to growing very large dahlia blooms if you want to give it a try)
As more buds develop on this stem, the blooms become smaller and smaller.
Pruning off stems will result in fewer but noticeably larger bloomss.
Step 10: Winter Care For Dahlias in Pots
Dahlias will often flower from mid to late summer all the way through to the first frosts, at which point, the tubers will need some protection.
Potted dahlia tubers are more susceptible to frost due to the lack of soil protecting them, so in most cases, they should be lifted, cleaned, dried, and overwintered, although this depends on where you live as some areas are warm and frost-free most winters.
Lifting and overwintering dahlia tubers is easy and a great opportunity to split the tubers to grow more plants and save money.
Richard Jackson Garden has a very informative yet straightforward explanation of how, why and when to lift and store dahlia tubers.
Dahlias are beautiful late-summer perennials that produce plenty of often large and eye-catching blooms, but they are tender and require more love and care than your average plant.
Here are the 10 key points again:
- Choose the right dahlia for your pot size and provide support for taller plants.
- Inspect the tuber and look for ones with an eye.
- Store dahlias in a protected environment away from frost until the right time.
- Give dahlias a headstart, especially if you live in a colder area where the summers are short.
- Choose a sunny spot within a reasonable distance of a tap.
- Develop a plan to deal with slugs, especially during the early growth spurt.
- Pinch out the centre stem.
- Choose the best compost and fertiliser for early leaf growth and bigger blooms later on in the season.
- Deadhead regularly and prune for specific results.
- Lift and overwinter dahlia tubers grown in pots or move the pot to a warmer location if possible.
Should Dahlias Grown in Pots be Treated Differently to Ones Grown in Borders?
Yes, pots are far more likely to dry out, and dahlias are more sensitive to dry soil than most plants.
Also, dahlias are top-heavy and will require a sturdy pot.
Slugs and snails are easier to protect against when the plant is grown in pots, and barriers can help.
Dahlia tubers left in small pots are also more susceptible to frost damage.
Do I Need to Split the Dahlia Tubers Every Year?
Dahlias tubers don’t need to be split every year, but you’ll get more plants if you lift and split them.
The tubers will form large bunches if left in the ground for many years, so it’s generally a good idea to lift and split them at least every few years or so.
How Can I Grow Really Huge Dahlia Blooms?
We’ve published a detailed guide to growing very large dahlia blooms on our blog but to summerise:
- Give them a headstart.
- Deter slugs aggressively as damaged leaves affect the plant’s potential to grow and bloom.
- Choose a balanced fertiliser in spring and a low nitrogen/high potash/high potassium feed from summer onwards.
- Prune selectively, so there are only a few central blooms on each plant.
- Deadhead immediately.
- Support very well with stakes or frames.
- Water deeply, and don’t let the ground dry out fully.
How Many Dahlias Per Pot?
One per pot is the general rule unless the pot is huge.
Dahlias prefer space, so avoid planting them too close to each other as one will dominate the other in the pot.
How Much Feed or Fertiliser Do Dahlias Need?
Dahlias are renowned for being hungry plants that soak up the nutrients from the surrounding soil, requiring much more fertiliser than most other plants.
Well rotted manure, chicken pellets and fresh compost can also help boost dahlia’s growth potential, especially if they’re grown in pots.
Fish, blood and bone is a great feed and is ideal for dahlias but it can be boosted further with liquid feeds for an instant hit.
Are Dahlias Poisonous?
Dahlias can be poisonous to horses, cats and dogs. They can cause skin irritation in some humans although many parts of the dahlia are actually edible.
More From Hannah Miller:
Hannah is a keen amateur gardener, mother and a former NHS administrator.
She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.
Hannah is a keen photographer, and you’ll find hundreds of her photos throughout this site. She also contributes to our blog; check out her latest posts here.
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