Answer: Transplanting is a huge shock to a plant; many of the tiny feeder roots are invariably damaged in the process. You don't mention whether these were purchased plants, or if they were moved from another garden location. Large plants that have moved from another garden location are even more vulnerable to transplant shock than nursery plants.
If the trees were indeed moved, then I suspect that the trees' roots were damaged in the transplanting process, and they did not have time to recover before winter. So even though there was plenty of water available to them, the trees may not have had the ability to take it in.
If the trees were from a nursery, then my first guess would be a soil/water problem. If your soil drains very quickly, then even though you had plenty of rain, it may not have stuck around long enough to help the plants. And it's possible that the rain simply drained off the rootball into the surrounding soil, away from the roots. If your soil is compact, on the other hand, the water could have puddled in the planting hole, suffocating the roots.
I would not fertilize the plants--I don't think that is the problem. Rather, I would try to evaluate the soil conditions and try to determine if that is a factor. Make sure the trees continue to have adequate water this spring, look for signs of new growth, and hope for the best. If the trees were planted by a contractor, you might check to see if they offer any guarantees.
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