Answer: There are two different types of plants commonly called periwinkle. Vinca is an evergreen perennial vining plant and you can soak the roots for a couple of hours to rehydrate them before planting. The other periwinkle, Catharanthus, is sometimes called Madagascar periwinkle, is an annual plant and the roots of these plant do not need to be soaked in water. Hope this clears up the confusion.
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