Answer: "The American Garden Book", written by the folks at the Brooklyn Botanic Garden, states that passiflora incarnata is hardy in zones 6 to 9. (Since parts of southwestern PA are zone 6, they may indeed thrive there. In fact, the plant is described as sometimes invasive.) However, I was not able to find a type that is rated as hardy to USDA zone 5. Passiflora caerulea is rated to USDA zones 7 to 10, and the reference states that often the stems are killed back to the roots in zones 7 and 8. Why not give P. incarnata a shot? Place it in a warm, protected spot and mulch it well in the fall, once the ground freezes.
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