Lifting and Storing Dahlia Tubers Over Winter

Illustration of a colourful dahlia border in a British garden

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Dahlias are tender perennials that provide vibrant colour from summer through late autumn, but they cannot survive freezing temperatures. To ensure they return the following year, the underground tubers must be protected from frost. Depending on your local climate and soil type, this is achieved either by lifting the tubers and storing them in a frost-free indoor environment or by leaving them in the ground protected by a thick layer of insulating mulch.

Table of Contents

Determining whether to lift or mulch

The decision to dig up dahlia tubers or leave them in situ depends primarily on your regional weather and the drainage of your garden soil. In most parts of the UK, storing tubers indoors is the safest method to prevent loss.

When to lift and store

Lifting is strongly recommended if you have heavy soil, which tends to be colder and more prone to waterlogging during winter. Because dahlias dislike cold, wet soil, tubers left in heavy clay are at a high risk of rotting. This method is the most reliable way to ensure survival in colder or more exposed regions of the UK.

When to mulch in the ground

Leaving tubers in the ground is an easier option and may be viable if you live in a milder region or have light, free-draining soil. However, this remains a risk; an unexpectedly harsh winter or a period of extreme wetness can still lead to the loss of the plants. Those that are mulched in the ground may also come into growth later in spring and flower later in the growing season than those that were lifted and replanted.

Timing the process

Protection should begin at the first warning of frost, which typically occurs between September and November. The ideal trigger for lifting tubers is when the foliage has been blackened by the first frosts. Use the local forecast and soil conditions as well as the calendar. RHS advice is to lift by late November even in a mild autumn, but lift earlier where severe frost or prolonged wetness is forecast.

How to lift dahlia tubers

Lifting requires care to avoid damaging the tubers, as any cuts or bruises can become entry points for rot during the storage period.

Prepare the stems: Cut off the old flowering stems, leaving approximately 5cm to 15cm of the stem above the base. These spent stems can be added to your compost heap.
Extract the tubers: Use a garden fork to gently prise the plant out of the soil. Avoid using sharp spades that might slice through the fleshy tubers.
Clean the tubers: Remove loose soil and debris by hand. Trim away any thin, insignificant roots.
Dry the tubers: Position the tubers upside down in a frost-free, airy place to drain, then allow the surfaces to dry. Check regularly and do not let them become badly shrivelled. This allows any remaining moisture to drain out of the hollow stems, reducing the risk of fungal growth.
Label: Ensure each cultivar is clearly labelled before storage, as dormant tubers can look very similar.

Storing tubers indoors

Once dried, tubers should be kept in a dark, cool, but strictly frost-free environment. A shed or garage is suitable only if it actually remains frost-free; a bright conservatory can also become too warm or too cold. Frost-free means avoiding freezing; the suitable storage range for tubers is a separate check. Use a thermometer and an appropriate cool, ventilated location.

Storage materials and method

Tubers should not be stored in airtight plastic bags, as they require ventilation to prevent rot. Instead, use shallow crates or open-topped wooden boxes. Fill these with a dry, insulating packing medium such as:

Dry spent potting compost
Sand
Straw
Newspaper

Bury the tubers in the medium, leaving the crown and short old stem above the packing material. Extra fleece or newspaper can slow temperature changes, but is not a replacement for a frost-free location. Check a minimum thermometer and relocate the boxes if freezing is possible.

Maintenance during storage

Storage is not a “set and forget” process. Check the tubers regularly throughout the winter. If you spot any tubers showing signs of rot, remove them immediately to prevent the infection from spreading to healthy tubers in the same crate.

How to mulch dahlias in situ

If you have opted to leave your dahlias in the ground due to mild weather and well-drained soil, you must provide a physical barrier against the frost.

Cut back: Trim the stems down to the base.
Apply mulch: Cover the crowns of the tubers with a thick layer of organic mulch. A depth of 15cm is recommended to provide sufficient insulation.
Choose materials: Effective mulching materials include homemade garden compost, chopped stems, well-rotted manure, or chipped bark.

Diagnosing and preventing storage rot

The most common failure in overwintering dahlias is tuber rot. This is typically caused by excessive moisture or poor ventilation.

Signs of rot: Tubers may feel soft or mushy to the touch, develop a foul smell, or show dark, water-soaked patches on the skin.

Prevention strategies:

Avoid early storage: Let surface moisture dry before packing, while avoiding excessive dehydration. Check for both softness/rot and severe shrivelling during storage.
Avoid wounding: For a straightforward beginner method, leave clumps intact until spring, when growing points are easier to identify. Any wounds created by dividing the tubers provide an entry point for pathogens. Save division for the spring when the tubers are starting into growth.
Ensure airflow: Use open crates rather than sealed containers.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Garden fork: Useful for loosening soil around a tuber clump; work well outside it because fork tines can also puncture tubers. Ensure the tines are sturdy enough for the soil type to avoid bending. Search Amazon for Garden fork.
Wooden storage crates: Provides the necessary ventilation and structure for storing tubers in sand or compost. Ensure they are open-slatted or open-topped to allow airflow. Search Amazon for Wooden storage crates.
Biodegradable horticultural fleece: An optional extra insulating cover, not a way to make an unheated freezing shed frost-free. Check material, durability and storage temperature. Reuse sound fleece where available; a biodegradable claim does not establish insulation performance. Search Amazon for Biodegradable horticultural fleece.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.