How to care for your dahlias in winter

November 17th, 2019 Posted In: Gardening know how

I never dig up my dahlias in winter. And I have grown dahlias – successfully – for fifteen years.

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

Do I have some secret knowledge about a Siberian weather front heading this way?

Even if I did, my dahlias survived the Beast From the East, as the sudden snows in March 2017 were nick-named.

Why not 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.

Dahlia 'Orange Cushion'

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

In fact some of my dahlias have loved it. After nearly 10 years in the ground, 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 the prosecution…

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

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!

And for the defence…

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

Both Steven Edney of The Salutation in Sandwich (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, crowns protected by a pile of mulch. 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.

How to care for dahlias in winter

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

It all depends on time…

Looking at my Orange Cushion over the years, particularly this year, I think the key is probably how long you leave them. 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 2018

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.

Dahlia 'henriette' in 2017

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.

I’m sure that would never have happened if I’d stored my dahlias in winter neatly in a dark, ‘frost-free’ place.

hybrid dahlia

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:

Next year, I’ll be leaving my dahlias in the ground again. Just not for so long this time!

 


5 comments on "How to care for your dahlias in winter"

  1. Francesca says:

    This is such a helpful and interesting blog post. Your photographs of dahlias are gorgeous too. Thanks for sharing your brilliant advice.

  2. Aqsa says:

    Very well said! I have grown dahlias for the first time this year and was battling between taking out/leaving them to overwinter. I’ll be going with your choice this year, thank you for the tips !

  3. ME says:

    Thank you for the dahlia edition. In Scotland the risk is too great so I dig them up and replant them the following year

    1. Absolutely – we are much milder here down south.

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