A guide to overwintering Dahlias in the UK

A question often googled is: “Can you leave Dahlias in the ground over winter in the UK?” Of course, the answer to this question will depend on many factors, including where you live, the severity of the winter, whether your garden is exposed to hard frost, etc. In this article, we will look at ways of overwintering Dahlias and preserving your plants for next year. After all, dahlias are perennials. You should be able to enjoy them from year to year.

Although dahlias are perennials, they are also tender. Special care is needed when storing tubers to protect them from hard frosts.

As the colder months encroach, you may need to dig up your Dahlia tubers and store them in a frost-free environment. However, there are alternative approaches. More on that later. Firstly, let’s have a look at overwintering dahlias in a frost-free environment.

When to cut back dahlias uk

In the United Kingdom, the optimal time to cut back dahlias depends on seasonal changes and the local climate. Dahlias are tender perennials, and in the UK, they are prone to frost damage during the winter months. To ensure the health and vitality of your dahlias, it is generally recommended to cut them back after the first frost has blackened the foliage. This typically occurs in late autumn, around October or November.

When cutting back dahlias, start by removing the dead and withered foliage and cutting the stems to about 15–20 centimetres (6–8 inches) above ground level. This helps prevent the spread of diseases and encourages the plant to focus its energy on the storage organs, such as tubers or rhizomes, below the soil. After cutting back, it’s advisable to lift the dahlia tubers from the ground, especially if you’re in an area with particularly cold winters. Store the tubers in a cool, dry place until the following spring.

By following these steps, gardeners in the UK can protect their dahlias from winter damage and ensure a vibrant display of blooms in the coming growing season. Additionally, this practice helps maintain the overall health and longevity of the dahlias, ensuring they continue to thrive for years to come.

HOW To overwinter Dahlias Tubers

How you approach this topic will largely depend on where you live in the UK. If you live in the north, then always take your tubers in during the winter and protect them from frost. If you live in the south, you may be okay leaving them in the ground, but make sure you cover them with compost.

Overwintering Dahlias, Step by Step

  1. During late October, cut the tops of your dahlia plants to encourage tuber development.
  2. In November, cut the stems of your Dahlias to between 3 and 6 inches from the ground level. Don’t forget to label the stumps so that you can keep track of each variety.
  3. Dig down to about 8–10 inches deep around each Dahlia plant with a fork. Ensure that you don’t damage the brittle tubers. Once you have loosened the soil, lift it slowly out of the ground. Be gentle! If Dahlia tubers snap during the digging process, they may no longer be viable.
  4. Remove any excess soil or compost from around each tuber.
  5. Remove organic materials such as thin or decaying roots and leaves. This will help prevent fungal infections and other diseases.
  6. Remove the ‘mother root’ or last year’s tuber.
  7. Leave them upside-down for a week to allow the tubers to heal.
  8. The Dahlia tubers must remain dry, but not dry out completely.
  9. Place it in a dry, frost-free environment.
  10. Evenly space it in a tray or box and fill it with sawdust, spent dry compost, or vermiculite.
  11. Cover with cardboard or add an extra quilt of fleece if you live in a colder climate.
  12. Keep an eye on your Dahlia tubers. If they dry out, spray a little water on them with a trigger spray.
  13. Check on them every couple of weeks and discard any rotten or mouldy roots to limit infection.

An alternative to lifting tubers

If you live in a milder part of the UK, then you might want to try leaving your Dahlias in the ground over winter. I like this method as it offers very little disruption to the plants. You will need to cover each rootstock with a ‘molehill’ of spent compost. This will act as a blanket against hard frosts, which may damage the tubers. You may also want to try covering your Dahlias with fleece, hay, or straw to protect them from the worst of the frost.

Tip: Make sure you feed your Dahlias with fish bone and blood during late spring to encourage vigorous growth and plenty of flowers.

Dahlias – when to plant – UK

Your tubers have survived the winter, and now it is time to plant them out again. The following guide to overwintering Dahlias is geared toward readers from the UK. Times and techniques may vary for other countries.

  1. Carefully place tubers in 2-3 litre pots of free-draining, general-purpose compost from March to early April.
  2. Cover each Dahlia with compost so that only the stump is visible. Don’t bury deeply. Dahlia tubers grow immediately beneath the soil level.
  3. Place pots in a frost-free and bright location.
  4. Water your dahlias. Don’t over-water, but ensure that the compost doesn’t dry out. Boggy compost will rot your tubers.
  5. After the risk of frost has passed, plant them in a sunny spot in fertile and well-drained soil.
  6. Space each Dahlia between 50 – 75 cm.
  7. Mulch around your plants with a 3-cm layer of compost. This will help retain moisture and block some weeds from competing with your dahlias.
  8. Flowering should start in early July.
  9. Dead-head your Dahlias daily.
  10. Enjoy until early November, and then overwinter your Dahlias for next year!

If you have enjoyed this guide on overwintering Dahlias, perhaps you would like to read our Overwintering Begonias post.

Geoff Hoyle, Dahlia expert

Here is a great video on everything you need to know about getting the best out of your dahlia plants. It is presented by Geoff Hoyle, a keen Dahlia grower in Bredbury, Cheshire. He not only takes you through planning, planting, staking, and propagation, but he also explains how to overwinter Dahlias in great detail.

Can I leave Dahlias in the ground over winter UK?

The answer to that question depends on where you live in the UK. If you live in the north of England, then the answer is no. You will need to bring your Dahlias in during the winter. If you live in the south of England, your dahlias should be able to cope with most winters. However, I suggest that if you are planning to leave Dahlias in the ground over winter, you should cover them with a generous layer of spent compost, wood chippings, or manure. Uncover them in the spring before they start emerging.

Do I need to cut back Dahlias for winter in UK?

Remove the old flowering stems 5cm (2in) from the base and discard any thin roots. By the time spring arrives, the old, remaining stems will become papery and eventually rot away.

How do I overwinter Dahlias in pots?

Cut away old foliage to leave 2–3 inches of stem. Lay the pots on their sides to allow the compost to dry out. Place in a greenhouse or shed and cover with fleece. In spring, tap away some of the old compost and repot.

Do dahlia plants return each year in the UK?

If you protect them during the winter, you should have dahlias each year. I have several hundred dahlias in my garden. I planted them six years ago. So far, I haven’t lost a single plant, and the tubers are getting very big!

When to cut back Dahlias UK

Cut back your dahlias during November or after blooming has finished. Cover them (if leaving your Dahlias in the ground over winter) or take the tubers into a frost-free environment. Cut each plant back to 2–3 inches. 

For more information on this topic, please read this article on overwintering dahlias in the UK by the RHS.

In conclusion, successfully overwintering dahlia roots in the UK is a rewarding and crucial step for ensuring the longevity and vibrancy of these beautiful plants. By following the recommended practices of lifting, drying, and storing dahlia tubers in a cool, dark, and well-ventilated space, gardeners can protect their prized dahlias from the harsh winter conditions prevalent in the UK.

The diligence invested in this process will not only safeguard the tubers from frost damage and rot but also foster healthier, more robust plants in the coming growing season. As guardians of these botanical treasures, gardeners play a vital role in the cycle of dahlia cultivation, preserving the heritage and beauty of these blooms for seasons to come.

By adhering to the guidelines outlined in this article, enthusiasts can navigate the winter months with confidence, knowing that their dahlia roots are tucked away safely, ready to burst forth in a riot of colours and shapes when the warmth of spring returns. In essence, the key to a successful dahlia display lies in the meticulous care given during the dormant winter period, ensuring a spectacular and flourishing garden in the months that follow. Happy gardening!

This Post Has 17 Comments

  1. Roy Sell

    You tell us to start in October and cut back in November; then tell we can enjoy flowers through to December. A conflict of dates.
    However, thanks for the over wintering advice.

  2. James Middleton

    Thanks Roy. Cut the tops (flowering parts) of your plants in October and then further down at the stem.

  3. Margaret Boccoli

    I enjoyed your video especially with visual advice and not a running commentary. Got
    Lots of useful tips and helpful advice and care for my dahlias. Hopefully I will be able to care and produce a splendid display next year. Thanks

  4. Caroline Maclean

    Very helpful demonstration on how to grow, stake, trim, label and store daliahs.
    Thank you very much.

  5. Allie Wharf

    Hi James. We’re going to leave our dahlias in the ground- when do you recommend chopping the stems and to how much above ground? Thanks. Good article. Allie

  6. Kathryn

    I would like to know what to do with Dahlias that have been in pots all summer, not in the border. Can I just put them into the garage as they are, or do I need to take them out of the pots and store them bare rooted?

  7. James Middleton

    Hi Allie,

    It depends where you live in the country. I live in mild South Devon. I always leave mine in the ground. If you live in a colder part of the country (or world), make sure you cover the soil above the tubers with mulch. I use spent compost. I normally cut the stems to about 8 inches above the surface, to help keep track of where they are. This helps when weeding. The stems normally fall away during the Winter.

  8. James Middleton

    Hi Kathryn,

    You could leave them in the pots and transfer them into a frost free place. They will need repotting in mid-Spring. Or, you could unearth them and store them in dry, spent composts or soil. I treat them like potatoes. I chit them in Spring, in shallow trays of compost. You can also take cuttings as they chit. They are quite easy to propagate at that point.

  9. Margaret Mortimore

    I would like to know please when I should uncover my dahlias as I left them in their raised bed over the winter but covered them with mulch and a fleece. We are still having morning frosts in Gloucestershire so I guess it is too soon yet?

  10. James Middleton

    Hi Margaret,

    I would suggest that it depends on how much mulch you have added. If it is many inches, perhaps scrape away the mulch, but keep a couple of centimetres on there, just in case you get a late frost. Dahlias are pretty tough though. Here in Dawlish (Devon), I don’t bother covering them at all and they always survive. However, we don’t tend to get hard-frosts. You might find that the Dahlias will start to poke out of the ground over the next couple of weeks. Some of mine have already started to.

    Best regards, James

  11. Sarah Green

    I forgot to lift my dahlia tubers so they remained in ground over winter. Should they have started to sprout by now

  12. James Middleton

    Sorry for the delay. I missed this comment for some reason. It all depends where you live in the country. If you live in the South, it should be fine. In the North, you really ought to cover the ground with a thick layer of spent compost. Remove the compost after the worst of the frosts. It has been a long time since you wrote this comment. Did they come up?

  13. SueB

    I have overwintered dahlias in my allotment for years but the plants are now getting too big. Is there any way of pruning them without lifting them? could I just cut away some of the tubers in situ?

  14. James Middleton

    Hi SueB,

    Thanks for your comment. I would cut your dahlias down to 3-6 inches from the ground level and cover them with 6 inches of spent compost or a good layer of mulch. How you go about this depends on where you live. I live in South Devon, and I do nothing over winter, and I still have dahlias every year. If you live further north, you will need to protect them. I hope it goes well.

  15. Grimrose

    I grew dahlias from saved seed,they grew to a small plant ,some flowered.I put them in my cold greenhouse end of October, where the foliage got frosted.They haven’t formed tubers yet do you think they will survive if I take of the foliage and give frost protection?

  16. James Middleton

    Hi. Thanks for your question. It depends on when you sowed the daliah seeds. It is odd that they haven’t formed any tubers yet. That should have happened fairly early on. Are they a dwarf variety? I think you are doing the right thing by putting them in the greenhouse. Daliahs are reasonably hardy. I live in Devon and keep mine in the ground all winter. Further north, you should protect them as best you can from the coldest nights of winter. Some people heap mounds of spent compost on them and scrape them back in the spring. For extra protection, try wrapping the pots with a little fleece or netting and straw. Let me know how things go in spring. You should start to see growth in April or May.

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