Dahlias can flower right up to December, but once the frost comes they are over. You can leave dahlia tubers in the ground over winter if they are in a sheltered position with good drainage, but if they are in an exposed site it’s probably best to lift and store the tubers to prevent frost damage.
'I recommend that you wait at least 10 to 14 days after your first hard frost before digging,' says flower farmer Erin Benzaken of Floret Flowers, as this allows the skin on the tubers time to toughen, making them less susceptible to rot.
Knock off as much of the soil as possible, leave them to dry and then wrap in newspaper or in wood shavings and store somewhere frost and damp free. They can then be replanted the following spring.