Do Dahlia Flower Every Year. Dahlias are not considered to be biennial. Dahlias thrive in rich fertile well-draining soil.
If you live in a cold climate and want to get an early start you can start your dahlia tubers in 1-gallon pots about two to four weeks before your last frost date. If your hardiness zone is 7 or below you have a choice. Underground the tubers multiply each year again like a potato.
Either grow dahlias as annuals or dig the tubers and store them until spring.
Click to see full answer. Similar to a potato the tuber sends up a shoot that becomes the plant which produces leaves and flowers. By dividing these tubers in the winter you can multiply the original plant and grow identical dahlia flowers. Christmas in the Spring Dahlias From Seed.