Answer: The Hibiscus syriacus or summer blooming Rose of Sharon shrub is considered winter hardy to zone 5. According to your zip code you are gardening in zone 5B or the warmer part of zone 5. It should be reliably winter hardy for you if planted in a spot with protection from sweeping winter winds and in well drained soil, meaning not in a soggy low spot.
The tropical hibiscus (Hibiscus rosa-sinensis) sold as a summer patio plant or houseplant would not be winter hardy for you outdoors in the landscape. It should not be exposed to temperatures below about 55 degrees.
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