Answer: Mums vary in their hardiness, so select a variety that is hardy in your area.
Next, it is best to plant in the spring so they have all season to become established and well rooted. Plant them in a sunny location with a soil that is evenly moist and yet well drained. This is important to their winter survival, because they will "drown" if grown in a wet location over the winter.
Trim them back to about four inches in late fall and mulch around the plants; snow is an excellent insulation against cold. If there is no snow you could consider covering them with a light and airy mulch such as oak leaves or evergreen branches. Remove these gradually in the early spring to avoid smothering the newly emerging growth.
Annual division helps keeps the plants vigorous and healthy.
Finally, sometimes a slightly raise bed and a sheltered location out of wind can help them survive better.
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