Answer: This plant should be reliably hardy for you. It does go dormant each winter and starts to grow again (from the roots) in the spring, about when the tulips bloom. It should be cut back in late fall or very early spring, then you can see the new growth beginning as the weather warms. I am not sure if you might have thought they were dead when in fact they were still dormant. The most common reason for losing them would be an overly wet soil. It should be evenly moist yet well drained meaning not sopping wet and not bone dry. I'm sorry you lost your plants.
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