Can you divide dahlia tubers in spring? Experts share their golden rules to get even more beautiful blooms this year but you need to act fast

Can you divide dahlias in spring? If you've got a clump of tubers that’s looking more crowded than a bank holiday beach, we've no doubt you've been wondering... and itching to get at them with your secateurs, too.

It doesn't matter whether you prefer to grow dahlias in pots or plant these dramatic, blousy blooms straight into the ground; knowing how to divide your tubers is every bit as vital to them thriving as, say, learning how to overwinter your dahlias like Monty Don.

Any green-fingered soul will know that timing is everything in the garden – whether it’s planting dahlia tubers, pruning, or, in this case, dividing. Still, while most experts advise setting to work just after the first frost, that doesn't mean a springtime division isn't a good idea, too...

Can you divide dahlia tubers in spring?

The short answer? Yes! The longer answer? Well, it's also yes... albeit with a few golden rules to follow.

'Dahlia tubers can be divided in autumn after digging up before the cold winter or in spring before potting ready for the season ahead,' explains Morris Hankinson, director of Hopes Grove Nurseries.

Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants. He established the thriving business in 1992, shortly after graduating with a Commercial Horticulture Degree from Writtle College, Essex.

'Spring, usually around late February to early March, is preferred by some gardeners because it is easy to see where to divide, ensuring each piece has some tuber (body), neck and a swelling "eye" or the growth bud where the plant will shoot from,' he continues.

'In springtime, the growth bud starts to swell, making it easy to see.'

Essentially, splitting dahlia tubers is a bit like cutting a cake – you need to make sure everyone gets a decent slice (or in this case, an ‘eye’ that will actually grow). And, as ever, dahlias are well worth the effort.

That's right: if you get this one right, you’ll be rewarded with even more of those stunning blooms come summer, and they might just bloom for longer too.

How to divide dahlia tubers in the spring

Now that we've figured out you can divide dahlia tubers in the spring, here’s how to do it properly…

1. Prepare your tools and tubers

Morris says that you must always use sharp pruners (we rate the Spear & Jackson 7159BS Razorsharp Advantage Bypass Secateurs from Amazon) or a knife to carefully cut through the crown and separate the tubers.

'Remove any dead, diseased, or damaged tubers – squidgy, rotting ones should be discarded,' he adds.

2. Let fresh cuts heal

If you’ve made a 'fish cut' (a division with an exposed inner surface), Morris says it's best to leave the tubers in a cool, dark place for a day or so.

'Fresh cuts are more prone to disease, so this gives them the time they need to dry off before planting,' he explains.

3. Plant and label

Once all of your dahlia cuts have healed, pot the tubers up as usual, making sure they’re positioned correctly.

'Don’t forget to label each variety to keep track of your blooms!' warns Morris.

What to do if you've left it too late to divide your dahlias

While you can divide dahlias in the spring, it's best to do this before the end of March. If you've waited too long to set to work, though, don't despair; Morris says stem cuttings are a great alternative.

'All you have to do is take a new shoot from the growing dahlia, remove the lower leaves, and dip the cut end in rooting hormone,' he says.

'Plant three cuttings per 9cm pot in well-draining soil and keep moist. The result? Free dahlias!'

FAQs

What happens if you don't divide dahlia tubers?

If you don't divide dahlia tubers, it's not necessarily the end of the world as we know it – although there are a few unhappy side effects.

'The tubers will continue to multiply underground, leading to a dense, tangled mass. This can result in smaller flowers and weaker stems due to competition for nutrients and space,' explains Christopher O'Donoghue, one of the co-directors at Gardens Revived.

Christopher O'Donoghue

A gardener with over a decade of experience under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018 to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres – many with historical significance.

While undivided dahlias can still flower, Christopher adds that the blooms will likely become smaller and less abundant as the plant struggles to sustain an ever-growing root system.

'Old, undivided clumps can develop rot, fungal infections, or pest infestations, which can spread and eventually kill the plant,' he continues bleakly, 'and, over the years, the tubers can form a massive, knotted structure that becomes more difficult to lift and divide later.'

When to divide dahlia tubers in the UK?

If you want happy, healthy, thriving dahlias with strong and long-lasting blooms, it’s important to know when to divide them in the UK.

'Generally, it's best to divide the tubers every 2-3 years in early spring before planting, or in autumn after the first frost when the foliage has died back,' says Christopher O'Donoghue of Gardens Revived.

If they're looking a little overcrowded, it's also worth dividing them to give them a little more space.

What to do with dahlia tubers in spring?

If you're not sure what to do with dahlia tubers in spring, the answer is simple enough: wake them up!

'If you lifted and stored dahlias over winter, you should check them over for rot or shrivelled tubers, as well as discard any that are soft or mouldy,' says Christopher O'Donoghue of Gardens Revived.

'Then, take care to place them in trays of moist compost in a bright, frost-free spot (like a greenhouse or windowsill), before lightly watering them.'

Christopher adds that you should divide tubers if needed at this point, ensuring each section has at least one strong shoot or eye.

'Once all risk of frost has passed, plant tubers 10–15cm deep in well-draining soil,' he finishes.

So, can you divide dahlia tubers in spring? Absolutely, so long as you follow all of our golden rules to ensure they come back happier and healthier than ever.

Happy planting...