It would be extremely rare to see hydrangeas dying due to frost. While foliage and stems might show damage, the roots should survive, especially if the plant is well watered before temperatures plummet and if the plant is kept well mulched or is winter protected. If you covered them with mulch, the typically need about 2-4" of mulch past the drip line. Any excess mulch can be reused elsewhere in the garden with other plants. Or bag the mulch for later use when you have to replenish mulch that has decomposed or has been blown away. Hydrangeas should be starting to peek through in March under normal conditions (either stems start to leaf out or new stems start to grow). Oakleaf hydrangeas tend to break dormancy first, followed by Big Leaf Hydrangea and then the rest.
Answered on March 9, 2022
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