Answer: I am assuming you mean bearded iris rhizomes here. They should be fine. They often sprout fresh foliage and it usually winters over in good condition. In spring, simply trim away any badly damaged or discolored leaves. During the times when temperatures fluctuate, check them to be sure they have not been heaved out of the ground by frost action. If they have, simply press them back in again as best you can. If on the other hand you mean iris bulbs, they too should be fine as long as the flower buds are still underground. Most spring bulbs are adapted to very cold weather as well as to temperature swings which are so common in the spring. You might mulch around but not over any sprouted foliage to help moderate the soil temperature a bit.
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