Written by: Crocus Plant Doctor Justin Turner
Last updated: November 2025
To lift or not to lift: The dahlia dilemma
Few plants bring such long-lasting colour and joy to the summer garden as dahlias. From neat pompoms to flamboyant dinner-plate blooms, they’re unrivalled for late-season impact and cut flowers. Although classed as perennials, dahlias are borderline hardy by nature, and their fleshy underground tubers can be damaged by frost or prolonged, wet winter ground conditions.
So, once autumn is in full swing, gardeners face the ‘perennial’ question: should I lift my dahlia tubers or leave them in the ground over winter?
The answer depends on where you live, your soil type, and how harsh your winters tend to be. As with many gardening decisions, it isn't always black and white. With milder winters becoming more frequent due to climate change, and many of us short on time and storage space, keeping tubers in the ground under a thick mulch can be a practical and sustainable choice, provided your soil drains well.
This article explains how to overwinter dahlias, whether that means lifting dahlia tubers and storing them indoors, or leaving dahlias in the ground with some protection, so you can enjoy strong, healthy plants year after year.
Understanding dahlia hardiness
Native to Mexico/Central America, dahlias thrive in warm, frost-free conditions. Their tubers can’t sustain cold — they begin to suffer around -2°C (28°F) — and if they sit in cold, wet soil for long, they can rot. The UK’s variable climate means that not every garden faces the same risks. A gardener in Cornwall or London might find dahlias overwinter happily in the ground, while someone in Yorkshire or the Scottish borders would lose them to frost. The key is to adapt your dahlia care to local conditions.
Unlike smaller bedding dahlias grown as annuals, these tuberous types are true perennials that can be kept year after year if protected from frost.
When and how to lift dahlia tubers
For most northern and inland gardens, or where soils are heavy and slow to drain, lifting and storing dahlia tubers remains the safest approach.
Wait until the first frost has blackened the foliage — that’s your signal. Resist the temptation to lift immediately, as tubers continue to mature and swell for a week or two afterwards, building reserves for strong spring growth.
Cut the stems back to around 15cm (6in) above ground level — this makes lifting easier and gives you something to hold. Make sure any labels are present, or re-written to enable identification. Use a fork to loosen the soil gently around the clump, taking care not to damage the tubers. Lift carefully and shake off loose soil.
Place the clumps upside down in a cool, dry, well-ventilated shed or greenhouse for several days to “cure,” which toughens the skin and reduces rot risk. When dry, trim fine roots and old stems before storing dahlia tubers.
How to store dahlia tubers over winter
Place tubers in shallow trays, crates or boxes filled with dry potting compost, coir, or vermiculite, keeping them separated to improve airflow and limit disease. Store somewhere cool, dark, and frost-free, ideally around 5°C (41°F).
Check every few weeks, removing any rotting tubers. Lightly mist those that shrivel. If a severe frost is forecast, cover trays with hessian or horticultural fleece.
In early spring (around March), bring tubers into gentle warmth. Pot individually in fresh compost, water sparingly, and wait for shoots before hardening off and replanting outdoors once the risk of frost has passed.
Lifting dahlia tubers offers several advantages. It protects them from frost, rot, and winter waterlogging, ensuring healthy regrowth the following year. Once lifted, the tubers can be easily inspected and divided to produce new plants, and starting them into growth indoors in spring encourages earlier flowering in the summer.
Lifting dahlia tubers isn't for everyone. It requires time, storage space, and regular checks over the winter to prevent rot or drying out. For time-poor gardeners, this can feel like added effort, especially if storage conditions are less than ideal or space is limited.
Overwintering dahlias in the ground
In milder parts of the UK — such as the south-west, southern coastal counties, and London — leaving dahlias in the ground can work perfectly well if the soil drains freely. After the first frost, simply cut back the blackened foliage to just above ground level, then cover around the crown with a 10-15cm (4-5in) layer of mulch such as straw, bark or compost. This insulates against frost whilst shedding or soaking up excess rain.
Mark the site clearly to avoid accidental digging. In exposed areas, add fleece or cloche protection in very cold spells. As spring arrives, gradually remove mulch to let light and warmth reach crowns, and watch for slugs and snails, which love tender new shoots.
Leaving dahlias in the ground offers several advantages. There’s no need for lifting, drying, or storing, which saves time and effort, and the tubers often start growing more quickly in spring since they remain settled in the soil. This method works particularly well in raised beds or well-drained soils, where moisture levels are less likely to cause problems.
However, there are also some disadvantages to consider. In heavy or waterlogged soil, tubers are at risk of rotting over winter, and in harsh conditions they may freeze. Early shoots can also be vulnerable to pests such as slugs and snails, so some monitoring and protection may still be required.
Dahlias in pots
Most tuberous dahlias grow best in open ground, though a few compact cultivars tolerate large containers of 40cm (16in) or more. Dahlias grown in pots are more vulnerable to cold, as roots are exposed to freezing air. Wrapping containers with bubble wrap or fleece and moving them to a sheltered spot can insulate them, similar to leaving tubers under mulch.
Soil and drainage considerations
Soil type often dictates success more than temperature. Heavy clay or poorly drained soil almost guarantees winter losses if tubers are left in situ. In such conditions, do you have to lift dahlia tubers every year? The answer is yes — or at least in most cases. Alternatively, grow them in raised beds or large containers where drainage can be controlled.
Conversely, light sandy or loamy soil in a sheltered, south-facing spot allows safe overwintering under mulch. Adding grit or coarse compost to the planting area in spring to improve drainage will pay dividends. If your soil stays wet or puddles in winter, lift your dahlias; if it drains freely and rarely freezes, they can likely stay put.
A balanced approach
Not all dahlias or winters are equal. Rare or cherished varieties may benefit from lifting, while common types can survive mild winters in situ. Some gardeners alternate — lifting every other year or leaving a few trial plants.
“As with many gardening decisions, it isn't always black and white. With milder winters becoming more frequent because of climate change, and many of us short on time and storage space, keeping tubers in the ground under a thick mulch can be a practical and sustainable option — provided your soil drains well.”
Whichever approach you take, observation and adaptation are key. With care in autumn and early spring, dahlias will reward you with months of spectacular blooms — proving that even the most borderline hardy plants can become reliable perennials in the right hands.
