Garden Care

Dahlias – How to overwinter within the UK

Dahlia are tender perennials and must be protected from hard frosts. Here is a guide to storing Dahlia tubers during the coldest winter months and an answer to the question: can you leave dahlias in the ground over winter?

I often hear the question: can you leave dahlias in the ground over winter? Of course, this 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 preserving your dahlia plants so that you can enjoy them from year to year.

There aren’t many flowers that can surpass the beauty of the less-than-humble Dahlia. Colourful, waxy and butter-scented; they are the must-have addition to any garden. But did you know that you can easily overwinter your Dahlias, so that you can enjoy them next year?

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

As the colder months encroach, you may need to dig up your Dahlias tubers and store them in a frost-free environment. However, there are alternatives. More on that later. Firstly, let’s take a look at overwintering our dahlia roots in a frost free environment.

How to overwinter Dahlia tubers

  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 3-6 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 them 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 to 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 in a dry, frost-free environment.
  10. Evenly space in a tray or box and fill with sawdust, spent dry compost or vermiculite.
  11. Cover with cardboard or add an extra quilt 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. Discard any rotten or moulding roots to limit infection.

An alternative to lifting tubers

If you live in a milder part of the UK, then you might want to leave your Dahlias in the ground overwinter. I like this method as it offers very little disruption to the plants. You will need to cover each root-stock with a ‘molehill’ of spent compost. This will act as a blanket against hard frosts. You may also want to try covering your dahlias with fleece, hay or straw to protect them from the worst of the frost. 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 is a description of when to plant your Dahlias if you live in 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 during March to early April.
  2. Cover each Dahlia with compost so that only the stump is visible. Don’t bury deeply. Dahlia tubers grow immediate 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 a fertile and well-drained soil.
  6. Space each Dahlia between 50 cm – 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 December and then overwinter your Dahlias for next year!

If you have enjoyed this guide on how to overwinter Dahlia tubers, 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 by Geoff Hoyle, a keen Dahlia grower in Bredbury, Cheshire. He not only takes you through planning, planting, staking and propagation, he also explains how to over winter Dahlias in great detail.

By James Middleton

An obsessive gardener since 1982. Day-time job - web designer and developer and University lecturer.

11 replies on “Dahlias – How to overwinter within the UK”

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.

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

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

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

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?

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.

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.

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?

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

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