The Ultimate Guide to Lifting and Storing Dahlia Tubers

How to overwinter dahlia tubers

By Hannah Miller at DIY Gardening

To lift or not to lift? That is the question!

Can you believe that some gardeners treat dahlias as annuals and throw them away at the end of the season?

It just seems such a waste.

If you live in milder parts of the country, you can probably get away with leaving your tubers in the ground over winter, provided you place a good layer of mulch over them at least four inches deep; this maybe enough to protect them from moderate frosts.

Maybe.

For the rest of us, overwintering is the best option, and it’s not that difficult.

Follow my 8 easy steps to guarantee your dahlias survive the winter and grow back healthy and strong next year.

Closeup of large pink and red dahlia flower
Large yellow and orange dahlia bloom

Step 1: You Will Need…

Here’s a list of everything you’ll need to lift and store your dahlias successfully:

  • A garden fork to lift them out of the ground without damaging them.
  • A brush for cleaning.
  • Newspaper and cardboard boxes.
  • Tags or labels so you can identify them next year.
  • Compost or fine wood shavings or vermiculite.
  • Secateurs and/or a sharp knife should you wish to divide them.
  • A cool frost-free place to store them, such as a garage.
  • If you live in the far north, you may need extra insulation, and hessian is perfect.

Step 2: Timing

You’ve probably heard that dahlia tubers are sensitive to frosts and should be lifted before or immediately after the first frosts.

While the tubers should never be subjected to frost, lifting them too early or even immediately after the first bout of frost is a bad idea.

The tubers need to swell up and mature before they’re lifted, and this usually happens after the first frost.

Pull them up too early, and they’ll be green; this means finding the eye will be difficult, making dividing them near impossible. Also, they’ll be skinny and far less likely to survive the winter period.

You’ll know when the first frost has got them, as they go mushy and black. The foliage, stems and flowers of dahlias are very sensitive to frosts.

As the dahlia tubers are under the soil, they’re unlikely to be damaged by early, light frosts, and in most areas, you can leave them in the ground for a few days or even a couple of weeks after the initial cold snap, even if the top growth looks dead.

This is a crucial step as the tubers put essential growth and maturity at this stage, it’s their final oomph before entering dormancy.

Obviously, if the weather forecast predicts harsh frosts, you’ll want to lift them, but they can easily survive a week or two into light, late autumn frosts.

If you’re worried about aesthetics, you can trim the dahlia stems, leaving a 6-inch stem at the base, or just leave them as they are.

Step 3: Dig ’em Up

After the dahlias have been left in the ground long enough to “cure”, it’s time to lift them.

The best way to loosen the dahlia tubers is to use a fork and gently fluff up the soil around them, but first I suggest trimming off the stems a good few inches above the tuber cluster; this will give you something to pull on gently.

The neck of the tubers is actually quite delicate and easily damaged, so take care here. You shouldn’t yank or pull the stem too hard.

While you can lift them with a shovel, there’s more chance of slicing or skinning the tuber, encouraging organisms to enter and thrive, leading to disease and rot, so a fork or hand tool is best.

Freshly dug dahlia tubers

Step 4: To Wash or Not To Wash?

I usually wash my dahlia tubers to remove any soil, but plenty of gardeners say this dampens them, and wet tubers are more likely to rot when in storage.

I think they’ll be just fine provided they’re dried sufficiently after washing, but either way, it’ll be easier to clean them with a brush than just your fingers.

Here’s how I do it:

  • First, snip off the excess tails; that’s the wispy ends of the roots.
  • Next, snip off the stem if it’s overly long; I leave at least 3 inches.
  • Hold the tuber bunch upside down and under running water.
  • Use a 1-inch painters brush to ease off any mud.

The next step is perhaps the most important:

  • Turn the bunch upside down and let them dry for at least a week, preferably in a garage or porch or somewhere sheltered.

If you want to divide your dahlias, I recommend washing them as this removes harmful organisms. If you don’t, then washing is entirely optional.

If you’re not sure whether to wash them or not, why not wash half and just use the brush to remove the dirt from the other half? Then, you can label them as washed or unwashed and then see how well they survive the winter.

Step 5: Should Dahlias be Divided After Lifting or in the Spring?

Dahlias tubers can be divided to create more plants, but each tuber must have an “eye”; if it doesn’t, then it won’t grow next year.

The eyes are often tricky to locate, especially if the tuber has only recently been lifted and/or is unwashed.

By contrast, it’s far easier to locate the eye and divide the tuber in the spring.

The only reason I can think of why a garden would divide them after lifting them is to save space. Tuber bunches can grow big, and if your storage space is limited, it might make sense to split them straight after you’ve lifted them.

You don’t have to divide tubers and they’ll have a better chance of growing next year if they’re left intact as each bunch will have several eyes.

Step 6: Preparing Your Box

I use cardboard boxes lined with newspaper, but I’ve seen gardeners use plastic pots, tubs and even hessian to store them,

Here’s my recommended method:

  • Trim the stem to within an inch of the cluster, being careful not to damage any eyes.
  • Cut a small 1-inch hole in each side of the box, near the top, for ventilation.
  • Line the base and sides of the box with old newspaper.
  • Place a 2-inch layer of dryish compost at the bottom of the box and lay the tuber bunches onto it, ensuring they don’t touch each other.
  • Infill with more compost until there’s space for extra tubers, and infill more until all the tubers are covered.
  • You can leave the stems exposed above the surface or cover them; it doesn’t matter, provided the tubers don’t touch each other.

The compost should be fairly dry but not so dry that it absorbs moisture from the tuber but certainly not wet that it rots it.

I usually buy a couple of bags of compost from my local garden centre and open them on my garage floor and aerate it for a week before I use them to store my dahlias.

Alternative to compost: Compost doesn’t wick the moisture away from the tubers so some gardeners use vermiculite or wood shavings but to save on costs and to simplify the process, I just use semi-dry compost, preferably a light, fluffy type.

Step 7: The Best Place to Store Dahlias Overwinter

And this is the big question I see being asked all the time; exactly where is the best place to store dahlia tubers over winter?

As a general rule of thumb, the tubers should be kept between 5° and 10°.

Below 5° and you’re skirting close to frosty conditions, and above 10°, the tubers may start to sprout.

In the UK, most gardeners will be able to keep them in sheds or garages. However, those living in the north may need to locate them in a warmer spot or cover them with breathable but insulating material, such as hessian or similar.

As for me, I have a porch cupboard that is relatively sheltered, and I’ll place the boxes on top of each other and against the outer house wall for a bit of warmth.

I recommend lifting the boxes off the floor by an inch or two at least.

The ideal humidity for dahlia tubers is well above 70° but this isn’t always possible in a garage or shed so I just make do with what I have.

Step 8: Keeping an Eye on the Tubers

Some of the tubers may rot, and these must be removed from the box before disease sets in and affects the other tubers.

I check the boxes once a month and fish out any squishy tubers; I don’t worry about any tubers looking shrivelled as that’s normal, as long as they are still reasonably firm.

If the tubers look really shrivelled, I may spray a little water into the compost to moisten it, but not enough to cause the tubers to rot.

Smaller dahlia blooms on stems
Pruning dahlia side stems

Summary

Dahlias can be grown as annuals, they can be left in the ground over winter with a layer of mulch on top, or they can be lifted and stored until spring.

I’ve had lots of success with the method described above, but others do things slightly differently, so don’t be afraid to try a different approach!

All of the dahlia photos on this page were taken by me in 2021 and all were grown from tubers I’ve previously divided from older plants over the years.

More From Hannah Miller:

This guide to lifting and storing dahlias was created by Hannah Miller and is part of our guide to growing plants and was last updated in November 2021.

You may also like our Ultimate Guide to Growing Dahlias.

Hannah is a keen amateur gardener, mother and a former NHS administrator.

She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.

Hannah is a keen photographer, and you’ll find hundreds of her photos throughout this site. She also contributes to our blog; check out her latest posts here.

Author Hannah Miller

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