Tips For Growing Dahlias In Pots | Horticulture Magazine (2024)

PERENNIALS > DAHLIAS > CONTAINERS

By ELIZABETH WADDINGTON

Dahlias are hugely popular garden flowers and with good reason.

There are a massive variety of dahlias to choose from, in a wide range of shapes and sizes, with lots of variety in bloom shape, size and colour.

Dahlias are commonly used in cottage garden-style borders, but where space is more limited, many dahlias can also be grown in containers.

“I absolutely love dahlias and think they work brilliantly when grown in pots,” shares Tamsin Westhorpe, a Garden Writer and Horticulturist.

“I think if you’ve got a small garden and somewhere indoors where you can overwinter the tubers, I don’t think you can beat a dahlia. You can cut them, they go on forever and they give you colour for a long time.”

When deciding whether you can grow dahlias in pots, the most important thing to consider is the size of the particular cultivar that you have chosen to grow.

Some smaller types are far better suited to container cultivation.

“Sometimes, the simplest forms of dahlias, such as the dark-leaved, open-centred varieties, can give a fabulous display in pots, with the added advantage that they will attract all types of pollinators,” says David Hall, manager and director of the specialist dahlia nursery Halls of Heddon.

Remember, while dahlias can work well in pots, it will usually involve a little more work and effort than growing them in the ground.

You will need to work a little harder to keep on top of the plants’ water needs and must strive to maintain fertility over time.

Many dahlias may need some support as they grow, and the container you choose will have to be sturdy and heavy enough to support taller growth.

Choosing A Container

When choosing a container for dahlias, you should choose a pot of sufficient size.

Though due to the root systems of these plants, it will not need to be particularly deep,as David explains:

“Obviously, tall varieties in pots are going to be much more vulnerable to blowing over so a wider-based pot will be more suitable.”

A pot around 30-40cm wide, and around 30cm deep will usually be large enough to accommodate most dahlia plants.

Containers should be sturdy and heavy enough not to blow or topple over – especially if you are growing a taller dahlia cultivar.

The container should of course have good drainage at the base.

Choosing Your Potting Mix

Fill your chosen container or containers with a good quality peat-free multi-purpose compost or a homemade blend, mixed with homemade compost or a well-rotted manure.

“I would recommendadding water-retaining gel to your compost, as it is important not to let Dahlias dry out too much,” Dan Ori, a Horticultural Consultant, recommends.

“You may be able to find a potting mix with it already added at some garden centres”

Potting Up Dahlias

If you have purchased a potted dahlia plant, the plant should be placed at the same depth in its new container as it was in its previous pot.

Make sure that there is growing medium all around the tubers and root system, and that there are no air pockets around the plant.

Firm the soil around the plant and water it in well. Mulch around the top of the container with organic matter.

“I’ve even found that the smaller bedding/patio types are better with some support, even if it’s just a few canes and some string around them to tie them in,” says David.

You should add your support when planting, so you don’t impact the growth of roots later on in the process.

You can also grow dahlias from tubers, from cuttings, or from seed.

Start tubers indoors around February, potting up divided tubers into individual pots when they are around 3cm high.

Place outdoors in May or early June, or plant them directly into containers outdoors from April.

Place a tuber with shoots around 10-15cm deep in your container.

If growing dahlias from seed, prick out seedlings into individual small pots, then harden off and place into their final growing positions (which can be in containers) in late May or June.

How Many Can You Plant Per Pot?

Typically, dahlias require a reasonable amount of space to grow.

Jack Gott, the owner of JRG Dahlias, recommends planting 3 dahlias in a large pot, but you should keep in mind that they do need some space to grow.

They should usually be spaced around 50-60cm apart.

So typically, unless using a very large container, you will grow just a single plant in each container to grow to maturity.

Potted Dahlia Care

Dahlias can grow well in containers, but do require some care.

“It is vital to provide sufficient water to plants in pots, including dahlias,” says Elaine from Dachshund Dahlias.

Water well in dry weather, trying to water soil and not splashing water on leaves or flowers.

It is best to water deeply, and less frequently rather than little and often, as shallow watering encourages shallower root formation.

Replenish mulch around the top of the container each spring for fertility and moisture retention.

Feed dahlias in pots once a week or so with a potassium-rich organic liquid plant feed.

Remember to stake taller cultivars for support, as June states:

“The plants will need to be supported, usually with 3 canes and some string.”

“The pots should also be rotated a 1/4 turn every other day to give the plant equal light and ensure equal growth,” adds June.

Look out for slugs, snails and other pests – remain vigilant to stay on top of any potential problems.

“Keep an eye out for insect damage and use an insecticide where needed, being careful to follow the maker’s instructions,” says June.

Harvest dahlias for cut flowers, and deadhead every week or so during the blooming period to encourage further blooms.

“Remove lower foliage to promote airflow and reduce issues with mould and rotting leaves,” says Elaine.

“You can easily tend to plants in pots as they are more accessible.”

After dahlias begin to die back in autumn and enter their dormant phase for winter, you can either move the container under cover into a frost-free location or lift and store the tubers in potting compost or sand in a frost-free place.

After all risk of frost has passed, you can move the dahlias back outdoors and they should regrow and bloom again and again over a number of years.