Dee,
No way full size hydrangea will be happy in 18" diameter hole. Even if you could fit it there right now, you simply will be caging it, restricting future growth and compromising the health of the plant in general. Also, if hole is shallow (you said there are rocks underneath) that is definitely not a right space for any, even dwarf hydrangea.
If 'this spot is just crying for a shrub there' consider small(ish), up to 3' at maturity Rhododendron, Azalea or Pieris (BTW, they have nice variegated Pieris at HD right now).

Red/orange roots has to be removed indefinitely.
Hydrangeas main roots are brown(ish)-gray and feeder roots are white-gray. You may cut those red brush roots and remove them piece by piece if they are too tangled.

Don't keep hydrangea out of the ground for long.
If you can't plant it ASAP, wrap a rootball in some kind of cloth and water it TWICE a day + mist leaves daily.

Thanks George. I didn't think that the hydrangea (or much of anything large, for that matter) could survive in such a small hole. But you know what? I was so determined to have that stinking hydrangea there, lol, that I went back out with my pickaxe and pulled out 3 huge rocks (once I start I kinda get obsessed, lol!). Of course my DH, who got up at 3AM this morning to go fishing, wakes up from his nap and strolls outside just after I finish! So, I ended up with a huge hole and had to find soil to fill it in, lol!

I did not, however, do any more detangling of the roots. Maybe I should dig it back up and finish the job? The hydrangea was thriving as it was until this summer with the drought and the added sun, so I guess the roots weren't that bad, but I hate to see that happen to a plant. Unfortunately, it seems to happen all too often in my yard. Roots everywhere - except where the rocks are!

:)
Dee

Good work, Dee! Isn't it great to move rocks? Gives you such a sense of accomplishment when those rocks are sitting above ground next to a newly planted shrub.

I would not worry about those red roots, since they are no longer attached to whatever plant they belonged to. I'd just keep an eye around the hydrangea and see if something like spirea start popping up out of the soil. They could have been from something like a maple, many feet away from the shrub, in which case they'll just rot away harmlessly.

DTD, it does feel great to get those rocks out! Thank goodness I have some compost/soil mix leftover from a spring delivery, though, so I could fill the gaping hole I dug, lol.

I hate those little roots. Like I said, they are everywhere in my yard, and no matter how I build my beds, even digging them, they re-appear and tangle in the roots of my perennials. In a couple of beds and around some individual shrubs, I have put in 12-inch deep pound-in edging - not to edge, necessarily, but to try to keep the roots out. But this gets expensive and isn't really the look I'm going for either, lol! Oh well, I'm sure within a year this hydrangea will be attacked by roots again anyway.

Thanks for your help, guys!
:)
Dee

FWIW, the plants I have been transplanting, hostas and hydrangeas, are entangled with invasive vine roots (red). In this case, I feel like it is my big chance to get ahead of the vines from the "root cause". The only way I was able to get the roots off was to begin by washing them off with a hose and dipping and swirling the root ball in a bucket of water. The good news is that the plants are doing much better after transplant. I think stopping the strangulation gave them anti-transplant shock! The hydrangeas I transplanted had very long roots with a slightly orange tint to the brown coating on fleshy white roots. The nearly wire like red roots were the vines. These are able to take over the planet from small bits of roots.

Congratulation on your rock harvest!

Dee, I'm tipping my hat to ya :)... Hubby harvested a nice crop yesterday in order to plant a 5' Ilex 'Dragon Lady' and he was still uttering unmentionables this morning as he crawled into the shower! haha Daniel Webster was right...we grow rocks the best in New England. I'm using my rocks for critter habitat since we got the Wildlife Refuge certificate. It's amazing how having that silly sign has made us so much more conscious of our actions around here. We're even looking at installing rain barrels next spring (assuming it EVER rains in CT again?). Anyway, congrats on your fall harvest...

Confounded, you use the same method I do - the hose and the bucket of water. This time, though, the vines didn't seem to want to come off the hydrangea roots the way they usually do, which is why I thought they just might BE the hydrangea roots, lol!

Tricia, I feel your DH's pain, lol! I'm looking into getting rain barrels too. Wish I had done it LAST year! It might have helped a bit this year to have that extra water. I just may wait till I see rain again with my own eyes, because I'm beginning to think that it will never rain here again!

:)
Dee