I have a couple of hydrangeas that I haven't planted yet and I want to put them in large pots by a couple of trees in my yard. They are mopheads but I don't remember if they are supposed to be Nikko Blue or Endless Summer. I got them from a local hardware store (box store).
Okay. So, the idea I am getting from most of the people I've talked to is that most plants do not winter well in a pot. They need to be in the ground. So, if I don't want to bring them in I'll need to put them in the ground?
In your zone they should be OK outdoors in a pot. Being in a pot tends to knock about a zone off the hardiness because the soil can get a lot colder in a pot than the soil in the garden bed, but I think most of NC is zone 7 and most hydrangeas are hardy into zone 5 so you should be OK. Unless you're in a colder part of NC of course...but if that's the case and you don't want to bring them in but do want to keep them in pots, you can dig a hole and sink the pots in the garden for the winter, that way they'll get the benefit of the insulating properties of the soil.
If you are in one of the Zone 6 Areas of NC, you need to find out if these hydrangeas, the ones that you do not know their name, are hardy in Zone 6. There are some mopheads that will not survive Z6 winters outside, even in a pot sunk in the ground. If you are in Zone 7, they can. But fill the sides of the hole with soil, compost or mulch.