Dahlias are not hardy and must be stored in a cool, dark place. Replant dahlia tubers properly in winter after they have been stored correctly.
The deeper the tubers are planted, the lower the risk of frost in autumn. However, flowering will start later. If there is another chance of frost after planting - for example due to the Ice Saints - you should protect the tuber with a winter fleece or with buckets. Plant perennials such as sweet candle, lavender and verbena as soon as possible.