Dahlias are native to Mexico where they were discovered by Anders Dahl, a Swedish botanist, according to Iowa State University Extension. Although the first dahlias were likely a single row of petals, or florets, with a yellow center, The American Dahlia Society recognizes 20 forms of dahlias, each sporting specific bloom types. Bloom size ranges from the tiny 2-inch pompom to massive 16-inch dinner plate varieties. With 15 official colors, dahlia blooms include traditional white, pink and red as well as bronze. Winterizing dahlias includes lifting and storing the underground tubers.
Cut dahlia foliage back to 3 to 4 inches from the ground level once they are killed by frost in the fall. Tag the plants to identify the color and variety.
Dig beneath the dahlia tubers with a spade or garden fork. Dahlia roots spread to a wide area. Use care not to injure roots or damage the tubers when digging.
Lift the tubers free of the soil. Shake to remove excess soil. Place dahlia tubers upside down in a shaded area to allow the stem to drain and soil to dry.
Remove dried soil by shaking or brushing the tubers with a soft brush. Although tubers can be washed, it is not necessary. If you wash the tubers, allow them to dry before storing.
Pour a 3- to 4-inch layer of peat moss or vermiculite into the bottom of a wooden crate or storage box. Layer the tubers over the peat moss. Cover with a 3- to 4-inch layer of peat moss.
Store in a cool area with temperatures between 40 and 55 F. Check the tubers once a month for signs of shriveling. If tubers begin to shrivel, moisten the peat moss. Avoid overwatering, as too much moisture invites disease.
Remove tubers in late spring and plant in a sunny location after the danger of frost has passed in your area.