Answer: There are a number of species within the hibiscus family, some of which are hardy outdoors in cold winter areas such as yours. However, 'rosa sinensis' is the tropical cultivar and will be damaged if left outdoors in winter. The roots are not hardy enough to survive, even if you mulch to protect the plant. I'd dig the plant and put it in a container to winter over indoors, but not until the weather begins cooling off in autumn. When growth slows and nighttime temperatures reach 55F, dig your plant, brush off as much garden soil from the roots as you can, and replant in a container of moistened potting soil. (The root mass will probably extend 12"-14" into the soil and at least as far out as the branch tips.) It's better to dig a generous hole than one too small. To help make digging easier, be sure to thoroughly soak the soil the day before.
When you move your plant indoors (do it gradually over a period of several days by bringing in at night and taking it out during the day so it can adjust to the temperature differences), put it in a bright spot without direct sunshine, keep the soil moist but not soggy wet, and mist the leaves occasionally. Flowering will stop in the winter and you can cut back the stems by 1/3 to help keep the plant bushy. In the spring, when the nighttime temperatures remain above 55F you can take your plant outside again.
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