When frost damages dahlia foliage, decide whether to protect the tubers in the ground or lift them. The safer choice for a treasured variety or a garden with heavy, wet soil is to lift, dry and store healthy clumps in a cool, dark, frost-free place. In a milder area with light, free-draining soil, some gardeners leave dahlias in place under mulch, accepting the risk of winter losses. These are the options in the Royal Horticultural Society’s dahlia guide.
Hi there, fellow DIYer,
The difficult part is less about the fork than about what happens after lifting. A wet clump in a closed box can rot. A shed that freezes is no shelter at all. A label, a dry clump and the right storage place make the spring restart much easier.
When should you lift?
The RHS advises waiting until the first frosts have damaged the foliage, then lifting if you choose to store the tubers inside. If frost comes late, lift by late November. That is a UK gardening guide, not a promise that every garden’s first frost falls in the same week. Watch the plants and local forecast.
A light frost on leaves does not automatically mean every tuber has frozen below ground. Even so, do not leave a valued clump exposed to a prolonged cold or waterlogged spell while waiting for a calendar date.
Can you leave them in the ground?
The RHS says this is possible in milder places or in light, free-draining soil, but an unexpectedly harsh or wet winter can kill the tubers. Cut back the stems and cover the crown with about 15 cm of mulch, such as garden compost or bark chippings. Heavy soil that remains cold and soggy is a stronger reason to lift.
| Your conditions | A sensible choice |
|---|---|
| Mild, sheltered garden with free-draining soil | You may leave a less valuable clump under 15 cm of mulch, accepting the risk |
| Heavy or wet soil, exposed site or treasured cultivar | Lift and store in a genuinely frost-free place |
| No frost-free storage space | Consider whether leaving in situ is possible; do not assume an unheated shed stays above freezing |
Lift, dry and pack a clump
- Label the variety before cutting it back. Once the flowers and leaves have gone, tubers look much alike.
- Loosen soil around the clump with a fork, working out from the stems. Lift from beneath rather than pulling the stems, and avoid spearing the tubers.
- Shake off loose soil and inspect. Trim damaged tubers and keep only healthy, undamaged material for storage.
- Cut stems back to about 5 to 15 cm. The RHS gives this range and advises leaving the rest of the clump intact until spring.
- Turn the clump upside down to dry. Hollow stems can retain water; the RHS recommends allowing them to drain and dry thoroughly over a few weeks in a sheltered, frost-free place.
- Pack in an open-topped box or shallow crate. Cover the clumps with dry spent potting compost, sand, straw or newspaper. Label the box as well as the plant.
The storage place should be dark, cool and frost-free. A garage or shed is suitable only if it stays above freezing. Add fleece or newspaper during very cold spells if needed, as the RHS suggests, but check the actual conditions rather than relying on the word “shed”. Do not seal wet tubers in plastic.
Check through winter
Inspect the stored clumps regularly. Remove any showing rot before it spreads. A tuber that is very shrivelled may have dried excessively; review the packing and storage conditions. Do not treat a fixed humidity or temperature range copied from another climate as a guarantee for a particular shed.
Avoid dividing clumps immediately after lifting just to save box space. The RHS recommends dividing in spring, because fresh wounds can admit rot during storage. This is especially useful if you are new to spotting growing points.
Start them again in spring
The RHS advises starting dormant tubers in pots of peat-free compost indoors or in a greenhouse. Keep them frost-free and in good light, and water sparingly as shoots appear. When dividing in spring, each new section needs roots and shoots. Grow the pieces on separately.
Young plants should be hardened off before planting outside after the local danger of frost has passed. In a colder UK district that can be later than in a sheltered southern garden. The RHS also describes direct planting of dormant tubers in mid to late April where conditions suit, even though foliage must still be protected from frost. Follow the method that fits your site.
Your storage note
| Variety or colour | Lifted on | Storage place | Winter checks | Spring result |
|---|---|---|---|---|
| Example: red border dahlia | After foliage frost | Frost-free garage, open crate | Check monthly | |
| Your plant |
A photograph of the flower beside its label saves confusion when every crate contains brown tubers. After that, the work is simple: keep the clump dry enough to avoid rot, protected from frost and easy to inspect.
Best wishes from Fred Schouten