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You can divide your tubers now, or you can wait and do it in the spring
. Make sure that when you do divide them, that each division has an 'eye' or new growth bud! Place the tubers in a bed of sawdust or vermiculite, inside a cardboard or wooden box.
Store them in a dry area where the temperature will remain at about 40 degrees F.
Check Dahlia tubers periodically during the winter, for signs of shriveling (moisten the storage medium),
or mildew (treat with a dry fungicide such as Captan)