The flower color change is just a natural progression for aging flowers, so no worries there.

But I have never heard of a bigleaf hydrangea being trained into a tree form - typically these are only done with paniculatas, one of the reasons being that there are no issues with pruning these, while the pruning issues with macs can be significant. Can you post photos?

Yeah, I have not heard of those either but maybe someone has started selling them. May be small in that case (has the look but cannot grow as tall as a tree). If they really are standard/tree hydrangeas, did you say macrophylla but meant paniculata perhaps? If you do not have access to a camera, do you at least know the name of the variety?

I posted two pictures, can you see them? I bought them at Costso. The tag says Hydranges Macrophylla Pink. That's it.

Scientifically, there is really no such thing as a tree macrophylla. They are normally sold a gimmick/novelty, and manipulated to look like a tree. A shrub is grown and branched out, then it is hacked down to a single cane with foliage atop. They are often staked or wrapped in tubing, as otherwise they'd likely fall over. The single cane can be as tall as 3-4' but no taller. If your single cane is 12" it won't get any taller.

Note that on all Macs, select branches die off yearly (each might last 3+ years), and if the main one goes, you'll be back to a new shrub from soil level.

Macs don't like hot soil either. You do have mulch there which is better than nothing, but the plant will suffer and dry out quickly without shade for the soil.

And since it's a mac it'll most assuredly put out sucker shoots yearly at the base, which you'll have to hack off if you want to maintain "tree form."

Aside from that, no pruning is required. But deadheading the flowers can help the plant get set for next year.

Naturally you'll want to overwinter these in a cold environment but above 32F.

Well, that's a new one on me!! But I'd hardly call them 'trees'.........more of a shrub trained as a standard :-) And they won't get tall like the paniculata trees.

Costco sells a lot of weird stuff. Recently local stores here featured lavender 'trees' - not a normal growth habit for lavender either and not really intended for long term growing. You will have to prune off any lower growth to maintain in that form. And depending on your location, planting them in the ground in fall may be the best way to overwinter them. And if so, I'd let them revert to their normal growth habit.

Less sun exposure on your potted 'trees' would reduce the flower discoloring and more rapid aging.

I am planning on overwintering in the ground. Will move them to more shade. Do you think color will come back or once gone it's gone?

Sorry - once the flower color is gone, it is gone! But any new flowers should have good color, at least initially.

Thank you all for your input. So do I leave these or dead head them? Will it produce more flowers this year or is it a one time bloom. No sucker shoots off main stem. but fresh leaves budding off of "branches"

It is your choice to leave or deadhead. Since these planters are in such a visible location, I'd be inclined to deadhead them. And since we do not know the variety beyond "pink mophead", it's impossible to say whether it will produce more blooms from new growth or not. I'd be disinclined to think one of the newer remontant forms would be suitable for training into a standard but you never know. It is just a matter of wait and see what happens :-))

Thank you. I did deadhead one flower and nothing new as of yet. We will see.

What USDA hardiness zone are you in? I wouldn't recommend overwintering a Mac tree in ground in anywhere less than zone 9, or at least anywhere that a Spring freeze won't take the whole thing out.

Zone 5. I'm in northern Illinois

Yeah you're taking a big risk in Z5. Normally a mac with an isolated clump of branches over a foot off the ground will end up biting it - a miracle if not!