Can I leave my dahlias in the ground during winter?

That depends on the winter

In a mild winter, dahlia tubers can survive in the ground reasonably well. But during a harsh winter, many dahlias will not make it. Dahlias are not frost-resistant. If you want to keep them, you’ll need to lift them from the soil after the first frost. When the foliage has died and become brown it means all nutrietiens are given to the tuber now. Cut the plants back to about fifteen centimetres, gently lift the tubers with a garden fork, and shake off the excess soil. Let them dry for a few days and don’t forget to label them with the name, colour or height. Then store them in a dark, cool and well-ventilated place. You can plant them again in spring after the last night frost.