When to plant dahlias in pots — garden experts say you should pot them up soon for a head start

Spring is just around the corner, and if you're wondering when to plant dahlias in pots, the wait is almost over.

Knowing when you should plant dahlias directly into the ground is one thing, but if you'll be learning how to grow dahlias in pots, are the rules the same?

Well, according to garden experts, you can get started as early as March (or even late February) if you'll be planting the tubers in pots — but it all depends on whether you'll be planting them outdoors or indoors to begin with. We spoke to them to find out why.

What you'll need

• Dahlia tubers, like Crocus' award-winning dahlias for pots collection
• A large pot like the Verve Mali Matt White Washed Terracotta Plant Pot from B&Q
• Multi-purpose compost like the Miracle-Gro Peat Free Premium All Purpose Compost from Amazon

When to pot up dahlias

To start with, we need to distinguish between planting dahlias straight into pots outdoors and potting them up, which usually happens indoors.

'Potting up' simply means planting the tubers indoors, in a container of compost, and waiting for them to develop into sturdy young plants before they're planted outside. In fact, this important step is one of Sarah Raven's golden rules for growing dahlias. But when should you get started?

'Here at Raby, we pot up our dahlia tubers in early spring, starting them into growth in the frost-free environment of the glasshouse,' say Becky Crowley and Dickon Harding, lead gardeners at Raby Castle, Park and Gardens.

Becky Crowley

Becky Crowley is assistant head gardener at Raby Castle, Park and Gardens and is working alongside the team there to ensure the vision of world-renowned garden designer, Luciano Giubbilei, is fulfilled in the remodelled Walled Gardens.

So, if you're wondering when to plant dahlias in pots indoors, with the end goal of planting them outside later in the year, you're looking at March or early April. If you really want to get ahead, you can even get started in late February.

'This early timing not only gives the plants a head start for summer, but also allows us to take cuttings from the fresh new shoots — perfect for increasing our stock of favourite varieties,' Becky and Dickon continue.

If you fancy following suit and propagating your plants, take a look at Monty Don's dahlia tips, which involve forcing tubers into early growth and taking cuttings.

Usually, your potted dahlias will be ready to plant outside from May or June, but make sure your area has seen the last of the frosts before you make a move.

Dickon Harding

Dickon Harding is gardens and landscape manager at Raby Castle, Park and Gardens in County Durham. He is responsible for overseeing the operation of the newly remodelled 18th century Walled Gardens and the role the five-acre space plays within the wider visitor attraction.

When to plant dahlias in pots outdoors

If you'd rather skip the potting up stage, or you miss the window, you'll probably find yourself wondering when to plant dahlias in pots outdoors.

You'll need to wait until the weather warms up, usually around late May or June, before you plant dahlia tubers directly outside (similar to if you were planting dahlia tubers straight into the ground). As we mentioned before, it's crucial that the last frosts are over before your tubers enter the big wide world.

It's also worth considering that potted dahlias started this way are likely to be more attractive to slugs and snails, which adore the young, tender shoots. That's why many gardeners, including Sarah Raven, swear by potting the plants up first — and no one enjoys researching ways to get rid of slugs in the garden.

Where to buy dahlia tubers for pots

It’s a good idea to do a little research before you buy tubers for pots, because some dahlia varieties are better suited to container-growing than others.

‘Smaller varieties of dahlias are ideal for planting in pots and containers, so make sure you choose a more compact variety that will grow to around 60cm,’ says Angharad James, product manager at Maxicrop®. ‘Larger than that, and they may be better off being planted directly into the ground.’

Here are some standout collections:

• Sarah Raven: Order in the Exclusive Dahlias for Pots Collection, which includes Dahlia 'Josie', Dahlia 'Molly Raven' and Dahlia 'Abigail'.
• Thompson & Morgan: Dahlia 'Autumn Shades Mix' does well in containers or borders.
• J. Parker's: Browse a huge range of dwarf dahlias.

FAQs

Do dahlias do better in the ground or in pots?

With the right care, dahlias will flourish in the ground or in containers. Just make sure they receive as much sunlight as possible, and try to grow them in a sheltered spot for best results.

That said, some varieties are better suited to container-growing, while others grow best in the ground. For example, larger dinnerplate dahlias (like the Giant Dinnerplate Dahlia Collection from Crocus) will flourish better in garden borders, while dwarf or smaller varieties will thrive in pots.

Will potted dahlias come back every year?

Potted dahlias absolutely can come back every year, but you'll need to learn how to overwinter dahlias to ensure they survive the colder months. This usually involves cutting back the top growth and bringing the pots inside to a cool, frost-free location for the winter.

If you're going to pot your dahlias up early this year, you can add the task to your list of garden jobs to do in March.