How to care for your dahlias in winter

November 17th, 2019
Posted In: Gardening know how

There is one big decision to make about looking after your dahlias in winter. Should you dig them up and store them? Or can you leave your dahlias in the ground?

This is partly – but only partly – about where you live. If you have a mild climate, with few or light frosts in winter and only short periods of snow, your dahlias are more likely to survive in the ground.

But they hate wet, cold soil, so if you get a lot of rain, leaving them in may not work.

I have grown dahlias – successfully – for twenty years. I have always been a fan of leaving them in, as I like easy gardening.

But this year I am digging up the dahlias. All of them. So what has changed?

To dig or not to dig up your dahlias in winter?

This post explains why I don’t usually dig up my dahlias. Our winters here in East Kent are comparatively mild. We don’t usually have long periods of frost and snow. Most of my dahlias have been fine with their dead foliage chopped off and their crowns protected by a pile of mulch or well rotted manure.

Ever since publishing my video ‘What You Need to Know About Dahlias‘, I’ve had comments from all over the world. And some people who live in colder climates have successfully left their dahlias in. It’s not entirely about how cold your winters are. It’s also about how wet they are – dahlias hate wet.

But you can have a surprising micro-climate in your garden – a sunny dry wall, for example.

Those with cold winters often treat dahlias as an annual, buying new tubers every year. If this is you, you’ve got nothing to lose by seeing what will happen if you leave them in.

But the colder your winter, the less chance you have of the dahlias surviving.

Dahlia ‘Orange Cushion’ has over-wintered in my border, under a crown of mulch, for nearly ten years. Excuse the aphids.

But whether you dig your dahlias up or not is not just about whether they will survive.

After nearly 10 years in the ground in my garden, Dahlia ‘Orange Cushion’ has expanded to fill most of the border, crowding out the other plants. It is now a wall of bobbing orange flowers and rather uninspiring, if abundant, foliage. While this is hugely admired from the kitchen window, something is just not right.

The case for digging up your dahlias in winter…

An exchange on Twitter with Withypitt Dahlias, Philippa Burrough of Ulting Wick (open for the NGS on various days and by appointment) and others clarified something in my mind.

Dahlias, like most plants, seem to go a bit feral if left entirely to their own devices. My ‘Orange Cushion’ flowers have been getting smaller and the mounds of foliage seem to have been getting bigger.

Withypitts Dahlias said ‘Leaving tubers in the ground will lead to weaker blooms, lacking intensity and clarity of colour. They degrade over time. Fine in the border, but not if quality blooms are wanted, and definitely not for Flower Farmers.’

My Orange Cushion dahlias should be fully double-flowered, according to Withypitt Dahlias, but leaving them in the ground for so many years hasn’t done them any good.

Dahlia ‘Creme de Cassis’ grown by Sue Oriel of Country Lane Flowers. Small flower farmers like Sue dig their dahlias up every year, partly because they need the space for the next crop and also because they need perfect flowers.

And Philippa Burrough added that she had just ‘dug up some that have been in the borders for quite a few years. Not what they were.’

‘As the tubers get larger,’ she explained, ‘they put up a large number of thinner stems, and therefore the flowers are less robust.’

So if you want exhibition blooms or to sell your cut flowers, you will have to dig the dahlias up every year!

But there are advantages to leaving them in, too…

On the other hand, I am not the only person to leave dahlias regularly in the ground over winter.

Both Steven Edney of The No Name Nursery in Kent (who comes from a family of dahlia growers) and Sarah Raven, who has restored dahlias to popularity, often leave dahlias in the ground in winter.

They protect the dahlia crowns by piling on a mulch, such as garden compost, on top of the plant. Both garden in South East England, which roughly equates to a USDA hardiness zone of 8b or 9.

Both say that most of the dahlias come through. They, too, are professionals and need a high standard of flowers.

However, in a professional garden, things are always changing. It seems unlikely that either Steven or Sarah would leave their dahlias in the ground for five to ten years.

I love this autumn view and the dahlias are a splash of colour, but less than they used to be.

You need to dig up dahlias at some point because…

Looking at my Orange Cushion over the years, particularly this year, I think the key is probably how long you leave dahlias in the ground. If  you don’t dig up your dahlias in winter – ever – things may go pear-shaped. ‘Rip City’ is another dahlia I’ve had in the garden since around 2011. Just this year, I noticed that the flowers weren’t as abundant as they had been.

Dahlia ‘Henriette’ in 2019. The stems aren’t as upright as they were two years earlier – or am I imagining it?

And ‘Henriette’, too, seems floppy and sprawling, with smaller flowers, compared to her usual neat and dainty appearance. She’s been in for five years.

And Dahlia ‘Henriette’ two years earlier in 2017. Has she got more vigour in this photo? Certainly the background is more dahlia-tastic.

So it’s out with the spade…

Actually, may I stop you there? Don’t dig your dahlias up with a spade. I did. I sliced through the dahlia tubers and broke the spade.

You do much less damage with a fork. I use an extra-light one from Kent & Stowe’s Garden Life range.  Note: links to Amazon are affiliate which means I may get a small fee if you buy through them. See disclosure. 

When I dug out the Orange Cushion tubers, I discovered there were over 100. All from one large tuber I planted in 2010.

Things had definitely got out of hand. And the tubers were all quite small, so I think they do need more space than they were getting. The original clump of tubers had got buried so deep that it’s still down there. I couldn’t even get it out.

Steven Edney says that you should store dahlias for winter somewhere dry, dark and ‘just frost-free’. A shed or garage is perfect. He stores his – when he digs them up – in spent compost, but you can also use straw.

I don’t think I’ve got enough spent compost for 100+ Orange Cushion tubers. Never mind the Rip City and the Henriette. They, too, have presumably run riot underground.

And another thing…

I planted a dahlia called ‘Con Amore’ a few years ago. It certainly lived up to its name, cosying up to the ‘Rip City’ next to it and producing a bi-colour dahlia that appears to combine the two.

That crossing of types is unlikely to happen if you store your dahlias in winter neatly in a dark, ‘frost-free’ place.

The love child of Rip City and Con Amore. Definitely a bit raffish.

More about dahlias…

See my video interview ‘Everything you Need to Know About Dahlias’ with Steven Edney here:

And you can drool over beautiful dahlia varieties in Dahlias – Beautiful Varieties for Home & Garden by Naomi Slade and Georgianna Lane.

Pin to remember how to care for dahlias in winter:

Next year, I’ll be leaving my dahlias in the ground again. Just not for so long this time! Do join us every Sunday morning for more gardening tips, ideas and inspiration. See how to follow by email here.