Cold is always a risk with many of of the best landscape plants. Those two plants are going to be very risky when temps drop to below freezing. You can cover them but it is no guarantee if temps drop to the 20's. They are considered worth growing however even if only as a warm season plant.
Flowering shrubs that will be dependably hardy for you include for part sun to shade gardenia, camellia, azalea and hydrangea, and for full sun Knock Out rose (a disease proof shrub type rose), yellow bells (dies to ground and returns in spring), and buddleja.
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