Advice
RHS Help & Advice
Overwintering Dahlias
Images: RHS/Leigh Hunt
Although dahlias can be left in the ground in milder areas, they are not reliably hardy and can rot on heavy soils, so most should be lifted and stored dry over winter.
Dahlias are best lifted once the foliage has been blackened by the first frost. Cut off the old flowering stems 5cm (2in) from the base and trim away any thin roots. These stems can be composted.
Use a fork to prise the plants out the soil, taking care not to damage, cut or bruise the tubers, as this can lead to rots developing in store.
Remove the soil from the tubers by hand or wash it off with a hose. If the tubers have been washed, position them upside down in a cool place
for a few weeks to dry off.
Label cultivars and lightly dust them with sulphur powder and bury in trays or wooden boxes filled with dry sand, soil or compost, leaving only the old flower stalks exposed. Place the trays in a cool but frost-free place, such as a garage
attached to a house or a shed.
Inspect all the tubers regularly and cut out any rot that develops with a clean, sharp knife and dust the cut surfaces with sulphur powder. In early spring shoots will appear, heralding a new season.