Answer: This plant Carex buchananii is described in the Monrovia online listing as being hardy into zone 5 so it should be able to overwinter in your area. I would be very careful however as some sources describe it as needing extra winter protection (such as deep mulching) to come through winter in your zone. You may want to mulch it heavily, just to be on the safe side. This plant grows best in full sun, in moist to wet soils. Sedge never grows very fast and the foliage tends to look dull so what you are seeing may be typical of this plant. However, if the foliage is discolored and dry (or rotting) and dead, go ahead and remove it now to allow the sun to reach the crown and encourage healthy new growth.
Best wishes with your sedge!
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