The dahlia plant is a perennial flower that is hardy in zones 7 to 11. While these growing locations do not require wintering dahlia tubers, growing zones that are wet or have cold winter climates should treat them as annuals and dig them for blooming the following season. The dahlia grows from a tuber underground that appears similar to a bulb. The difference is that tubers are not winter hardy in cold climates like bulbs are.
Cut the dahlia stems down to 6 to 8 inches in height one week after the first winter frost of the season.
Dig the tubers out by gently poking a pitch fork into the ground to lift the tubers out. Rinse soil remains off the tubers and remove the stem remains. Also remove and discard broken and rotten tubers along with the main mother tuber.
Place the tubers in a dry location that is above freezing for three to five days. The tubers must be dry prior to placing in storage.
Store the tubers in a box made from cardboard, wood or plastic. Fill the box with an even mixture of lightly dampened peat moss and sand and bury the tuber underneath. The peat moss should only be dampened so that when it is squeezed no water drips out.
Place the box in an area that is cool and dark. The temperature must be above freezing, ideally approximately 40 degrees F. Periodically check the tubers to make sure they are not drying out. Spray lightly with water if they seem dry or are starting to shrivel. Tubers that are too wet should be removed and laid on newspaper to dry out for several days. Sprinkle lightly with fungicide to prevent rotting.
Divide tubers in spring if they were wintered as a clump. Make sure there is one or more prominent bud on each section. Dust the tubers with a fungicide powder and let them dry for two or three days. This allows time for the open surface from dividing to heal before planting.