Dahlias are brightly colored flowers native to Central America. These plants, which come in a variety of shapes and sizes, are treated as perennials in zones 7 through 11. For cooler climate zones, the tuberous roots (known as tubers) must be dug up in fall and stored over the winter. If dahlias are stored in a damp location, mold can grow on the tuberous roots. If the tubers haven't become soft with rot, you can save them by treating the mold and storing them properly.
Rinse mold away carefully under running water.
Inspect dahlia tuber for soft areas that indicate rot. Slice off any soft areas with a sharp knife, leaving the eye of the bulb.
Discard any tubers that have rotted in the eye section. These will not grow.
Mix a solution of 10 percent bleach and 90 percent water in a bowl.
Dip tubers in bleach to kill any remaining mold spores.
Lay down newspaper in a dry, dark place. Put tubers on newspaper to dry.
Fill a brown paper bag with sawdust. When tubers are dry, place them in the paper bag and fold the mouth of the bag closed. Tubers should be completely buried in sawdust and should not touch one another.
Place bags of tubers in an empty milk crate so that there is plenty of air circulating through the crate and bags. Place milk carton in a dry, dark place with good air circulation to store until time to plant them.
Check your tubers every two weeks to ensure that mold has not returned.