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Overwintering dahlia tubers

23 June 2022

When a frost snap has touched the last dahlia flowers, it’s time to dig up the tubers. Dahlias are not frost hardy and cannot be overwintered in a flower bed – they must be dug up and stored in a frost-free place. 

In October, the first frost usually arrives in most parts of Sweden and the dahlias have come to the end of their work for the season. But the great thing about dahlias is that you can overwinter them so you can enjoy these beauties next year too – and divide them so you have even more! What is needed to overwinter dahlias is a frost-free place that is dark and dry.

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Protect with fibre cloth 

Dahlias remain beautiful and bloom well into the autumn, but when the frost comes, the pretty flowers die. For the first few frosts, you can protect them with fibre cloth, but when it gets too cold they freeze, leaving you with brown stems in your flower bed.  

Label the tubers 

It may be a good idea to label your dahlias before the frost touches them and they become unrecognisable. Write down information that will be helpful in the spring when it’s time to get the tubers back in the ground, such as the name, height, colour and size of the flowers. One tip is to write the information on a bamboo plant label or sticky label and tie it around the lower part of the stem using string. 

Digging up the dahlia tubers

Take care when digging up your tubers as they can be easily damaged. Use a pitchfork if you can – you can easily damage the tubers if you dig them up with a spade. If you do use a spade – be extra careful.

What to do: 

  1. Insert the pitchfork a little away from the tubers and coax them up. 
  2. Gently shake off the soil. 
  3. Use pruners to cut the stem about 10 cm from the tuber. If the stem is really thick, you can use a bigger tool, such as a pair of loppers. 
  4. Make sure the label is still attached. 

After these steps, there are a couple of different approaches. If the place where you are going to store your tubers tends to be a bit hot and dry, it might be a good idea to keep some soil around the tubers to prevent them from drying out. However, if it’s on the damp side, the soil may cause the tubers to mould, so rinse the tubers with water and leave them to dry. 

Once the tubers have completely dried, all the rot has been trimmed away and they look good, it’s time to pack them into boxes, trays, cartons or whatever you choose to store them in. You can wrap the tubers in newspaper or put them in peat or wood shavings. 

Tip! Experiment and see what suits you and your storage needs best!

Storing dahlia tubers for the winter

The optimal place to store your tubers is frost-free, dark and somewhat dry. Examples are in a shed, garage or basement. Ideally, the temperature should be around 4–8 degrees. Get to know your storage places and adapt overwintering accordingly – the most important thing is that the tubers are not exposed to any frost. If it’s a bit too dry, you can spray a little water on the tubers from time to time, but if it’s a bit too damp, mould can form and it’s important to remove all the mouldy parts as these can spread to the healthy parts. 

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Keep an eye on the tubers

During the winter, it is important to check the tubers from time to time to make sure that mice haven’t eaten them and they aren’t beginning to mould. 

Overwintering dahlias in pots

If you grow dahlias in pots, you can store them in the pots over the winter. Put the pots in a frost-free place and just replant the tubers in new soil in the spring before moving the pots back outside. 

Dahlias sown from seeds

If you sowed dahlias from seeds in the spring, these plants will have formed a tuber over the summer too. Dahlias sown from seeds are dug up and stored in the same way as dahlias grown from tubers.