You didn't mention the type and size of Hydrangea you are relocating, but if it is a big-leaf type(macrophylla) and very large, it will have a large root system. Dig a root ball as large as you can handle, with as much help as you can round up and wrap it in a plastic tarp to conserve the moisture. You might even place a bundle of wet newspapers inside to increase the humidity.
Plant the rootball at the same depth as it was at the former location and soak it well. Add a thick layer of mulch over the roots and water it often to keep the soil moist, not soggy, until it becomes re-established, which may take a year or more. A soaker hose coiled over the root area is an ideal way to provide the needed moisture. Adjust the on-off cycle to suit your needs. If many of the roots were severed during removal, it would be a good idea to remove some of the stems to reduce evaporation and the demand for water uptake. You can safely remove up to one-third of the stems and their foliage. Once established in it's new home, it will begin adding new growth each year.
Wear a back support and lift with your legs! Unless you have mechanical means to handle them, which I never did and I have moved some so large that I had to pull them out of the hole with a chain and pickup truck and tug them up a ramp to load them(with help, of course!).
Good luck!
Rb

We transplanted six in late February or maybe it was early March. They were well established plants and some were rather large. We made sure the hole was plenty large so we didn't have to mess with the roots while putting them in the hole. Added bone meal and some good garden soil and kept them watered well. They already were setting buds and green nodes on all when transplanted. Well, now three of the six that we kept have flowers opening and the leaves are healthy and a deep green. (We had moved them due to heat load in the summer.)

We gave several more away to friends and have heard they are all doing well. The last bunch to be picked up was over a week after we had dug them up and they now have blooms! I kept them in a large trash bag with water.
They seem to be pretty durable plants. Good luck!

I need to transplant a mophead (prob. Nikko Blue) back to its orig. home at west end of our front porch. We had to move it 2 years ago to a spot too shady for it, because we were getting a new septic system & the entire area would be torn up. It did not like the shade much & did little blooming, but that was OK, it was temp. Now we have sifted out the rocks the contractor left in our soil, and added compost, manure, and sand (we have heavy clay) & are ready to return hydr. to its home.
Now I need to ask, are hydrangeas shallow or deep- rooted? Do they make a taproot, or spread out a thready network? We don't want to dig into the soil near the plant & sever more roots than we should. It's been 2 years in the temporary spot so we know it has settled in.
Also, should we prune it back--partly to help us move it, and also to give it a rest next year from blooming, and let it concentrate on making roots? I'd like the blooms, of course, but if it is better for the plant in the long run I'll cut it back for the transplant.
Any advice on the type of roots they make? Thanks so much!

I have a hydrangea that has a partially exposed root ball. I just want to replant it in the same spot, just in a deeper hole. It's April though, so I'm concerned if I can safely do this or not. I'm not exactly sure what kind it is, but the blooms were lavender originally, then late last summer they turned pink. Any suggestions on this?