Answer: The best time to prune is late winter/early spring, before the shrub starts to grow. Nandina's growth habit is to produce tall, branchless stems that grow from the basal crown - it can't be trained to a softer, mounding habit like your other shrubs. To prune, cut one-thrid of the oldest, sprawling stems right back to the ground annually. It's not evergreen north of USDA Zone 8, and you're in Zone 6 or 7, hence the leaf drop. To grow healthy, vigorous, and attractive, it requires a deep, rich, moist soil.
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