Answer: According to the Monrovia web site, this plant, Nandina domestica 'Monum' or Plum Passion Heavenly Bamboo is winter hardy to temperatures as low as 0 to minus ten degrees F. It is typically listed as hardy to zone 6.
In addition to the nomimal zone description, hardiness also depends on the microclimate in your yard and the overall health of the plant. In a protected spot in town for example, sheltered from the wind and with some reflected heat from buildings, it would have an improved chance of coming through the winter in better shape than it would out in a windswept hilltop. Its chances will also be better if it is watered as needed into the fall and until the ground freezes, and with a generous layer of winter mulch over the root zone (but not up against the stems). Reliable snow cover can also be helpful in providing some insulation from the cold. Finally, an established plant is usually more resiliant than a newly plant one could be.
In my experience, nandina may discolor and defoliate in the colder winter areas such as yours, even if it does manage to survive and be root hardy. In severe winters it may die back to the ground as well, although usually they manage to send up new stems the following summer.
Whether or not this will be satisfactory to you will depend on where you have planted it and how visible it will be in the winter months. Further south, in warmer zones, it is a nicer evergreen presence in the garden and very dependable.
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