Not impossible at all, although you may need another set of hands or two to make it easy. Do it ASAP - the ideal time would have been while the plants were still fully dormant, but you should have enough time to do so now and get them settled in before hot weather. Make sure the new planting locations are dug and prepared first. If large plants, try to take as much of the rootball as possible. You won't be able to get it all if the plants are well-established. They'll be heavy so place them on a large tarp after digging and drag them to their new home. And don't prune any topgrowth now. Wait until they are in and settled and see first what kind of transplant shock they might experience, then prune out any growth that looks like it is failing. They need all that topgrowth to support the growth of new roots to replace those that might have been damaged by digging.

Most tree-style hydrangeas are paniculatas as they really get quite tall. Let the soil remain moist well m lched and try not to overdo the watering. No need to fertilize until next year if the potting mix came those round fertilizer pellets. Just so you cover all bases and just so your warranty remains valid, call them now and register "the problem" in case you end up having to return it. But frankly, I would not consider it "a problem" yet as they probably grew it in weird conditions and it is simply slow leafing out. A paniculata planted on the ground should have started leaf out in Zone 5 by now (but I am not sure of Zone 4 though). Flower buds will be visible much later, in mid to late June (there are some paniculatas that will have flower buds real late in July). Luis

Yes. Feel free to deadhead the flowers during the winter months or at the start of Spring. Add them to a compost pile or use them as mulch under the shrub (provided you do not have fungal issues). When do the leaves dry out or when do the hydrangeas leafout in your zone?

Thanks. That was my gut instinct, as it is difficult to tell what is still living. Some branches that looked dead actually had new growth sprouting further up the plant that I didn't notice until I'd already cut it off. Any idea what variety they might be? Or are they too sickly to ID?