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Garden Chrysanthemums (Chrysanthemum x morifolium cultivars) are hardy to -20º F/-29º C, if planted in a well-drained and insulated spot. Now would be a good time to cut down the stems. Enjoy the last flowers in a vase indoors. The snow will insulate the plant from the the cold, but additional insulation helps. It should be something that breathes. I particularly like wood chips for this, but other materials such as twigs, potting soil, pine needles etc will work. remember to take back the mulch in early Spring.