How to overwinter dahlias in the UK

By Sophie Sparkes · October 2026 · 6 min read

Dahlias flower right up until the first frost, then turn black overnight. That is not the end of them. The tubers underneath are alive, and with a little care in October and November they will flower again next summer, often bigger than this year.

Short answer: wait until the first frost blackens the leaves, then cut the stems down to 10-15cm. In a cold or wet garden, lift the tubers, dry them upside down for about a week, and store them in dry compost or sand somewhere dark and frost-free, ideally 5-10°C. In a mild, well-drained garden you can leave them in the ground under a 10-15cm mulch. Dahlias in pots can simply be moved, pot and all, into a frost-free shed or garage and kept dry.

Why dahlias need help over winter

Dahlias come from the mountains of Mexico and are only half hardy. The leaves and stems are killed by the first frost, and the tubers themselves rot if the soil around them freezes or stays cold and waterlogged for weeks. In practice, wet does more damage than cold. A tuber in free-draining soil can come through a few degrees of frost; the same tuber in heavy clay that sits wet all winter often turns to mush.

Lift or leave? How to decide

• Leave them in if you garden in the south or a sheltered city, your soil drains well, and you are happy to risk losing the odd plant. Many gardeners in mild areas have left dahlias in for years.
• Lift them if you are in the north, Scotland, a frost pocket or a rural inland garden, if your soil is heavy clay, or if they are precious or expensive varieties you do not want to gamble with.
• Not sure? Lift your favourites and leave the rest. That way one bad winter cannot take everything.

When to lift dahlias

Keep deadheading and enjoying the flowers until the first frost, which in most of the UK falls between mid-October and mid-November. When the leaves turn black and limp, that is your signal. Lift within a week or two, before the ground gets very wet or frozen. Letting the frost hit the foliage first is useful, because it tells the tubers the season is over and helps them ripen for storage.

How to lift and store dahlia tubers

1. Cut the stems down to 10-15cm and tie on a label with the variety name. You will not remember which is which in April.
2. Dig carefully with a fork, starting 30cm out from the stem so you do not spear the tubers. Lift the whole clump gently; the necks where tubers join the stem snap easily, and a tuber without its neck will not sprout.
3. Turn the clump upside down and leave it somewhere dry and frost-free for about a week. Dahlia stems are hollow and hold water, which rots the crown if it drains back down.
4. Brush off the loose soil once it has dried. You do not need to wash the tubers.
5. Pack them in a crate or box of barely damp compost, sand, vermiculite or scrunched newspaper, with the crown just showing at the top.
6. Store somewhere dark, cool and frost-free, ideally 5-10°C: a frost-free garage, cellar, spare room or under the stairs. A shed only works if it stays above freezing.

Checking stored tubers over winter

Have a look once a month. Soft, mouldy patches should be cut out with a clean knife back to firm flesh, and badly rotten tubers thrown away so the rot does not spread. Shrivelled, wrinkled tubers are too dry: give the packing material a light mist of water. Firm and slightly plump is what you want.

Leaving dahlias in the ground

After the first frost, cut the stems to ground level so water cannot run down into the crown. Then spread a thick mulch, 10-15cm deep, over the top: garden compost, bark, leaf mould or straw all work. Mark where they are so you do not dig into them in spring. If slugs are a problem in your garden, watch for new shoots in April, which they love.

Dahlias in pots

Pots are the easiest of all. Once frost has blackened the leaves, cut the stems back, stop watering, and move the whole pot into a frost-free shed, garage or greenhouse. Lay it on its side so rain cannot get in if it has to stay outside under cover. Keep the compost almost completely dry until spring. Compost in a pot freezes much faster than soil in a border, so pots left outside in the open are the ones most likely to be lost.

Waking them up in spring

In March or April, pot up stored tubers in multi-purpose compost and start them off in a greenhouse, porch or bright windowsill, watering lightly until shoots appear. This is also the moment to divide big clumps: cut them so that every piece has a bit of the old stem with at least one bud, or eye, on it. Plant out once all risk of frost has passed, usually mid to late May in the south and late May to early June further north. Dahlias left in the ground will push through on their own once the soil warms.

Dahlia overwintering questions

What do you do with dahlias in the winter in the UK?

Either lift the tubers after the first frost and store them dry and frost-free at around 5-10°C, or, in a mild garden with free-draining soil, cut them down and leave them in the ground under a 10-15cm mulch. Dahlias in pots can go into a frost-free shed or garage, kept dry, until spring.

What do I do with dahlias after flowering?

Keep deadheading until the first frost, because they will carry on flowering into autumn. Once frost blackens the leaves, cut the stems down to 10-15cm and either lift the tubers for storage or mulch them where they are.

Can I leave dahlias in pots over winter?

Yes, as long as the pot is somewhere frost-free and dry, such as a shed, garage or greenhouse. Stop watering once the foliage dies back. A pot left out in the open is at real risk, because the compost freezes right through and stays wet.

Do dahlias come back every year?

Yes, they are perennials. The top growth dies each winter, but the tubers survive if they are protected from frost and waterlogging, then sprout again in spring. Clumps get bigger every year, which is why many gardeners divide them.

Should I cut back dahlias before winter?

Yes, but wait until frost has blackened the foliage. Cut the stems to 10-15cm if you are lifting them, or to ground level if you are leaving them in, so water does not collect in the hollow stems.

Can I store dahlia tubers in a shed?

Only if it stays frost-free. An uninsulated shed can drop well below freezing on a cold night, which kills stored tubers. Wrapping the storage box in old blankets or bubble wrap helps, but a frost-free garage, cellar or spare room is safer.