Cutting the root will in all likelihood not kill the tree; however, when you cut any tree root, it stimulates the cut end to grow even faster, so it's a pretty temporary solution at best. The surface roots around the tree indicate that the soil is so compacted that roots will not grow in it because it lacks sufficient air space. If the house foundation is a slab, I think you're right to be concerned about potential damage. The roots have entered an environment that is looser than the surrounding soil with lots of air and moisture. They will grow larger and larger and can in time crack the slab. A block foundation is also pretty vulnerable to root damage. A poured concrete foundation is the least vulnerable, but the first hair-like roots can still enter the tiniest crack and begin expanding. There are products which are sold as root barriers. Their installation involves a lot of digging and they are far from totally foolproof, but it might be worth checking with a tree or landscape company. It might be possible to cut the root and then install a barrier around the foundation side nearest the tree.

My cuttings usually lose their leaves. Sounds like you had good success on rooting them. Do not feed them until they have started putting on "grown up" leaves. I just uncover mine a little more every couple of days until they are more than half uncovered. You can leave them in the cups until the cups are full of roots. then I pot them in larger pots. I am afraid to put them straight in the ground with it so hot. I would keep them in the same place where you have them now.

Cori Ann, I was able to root other roses, not florist roses. I only ever got one florist rose to root. And yes I understand there is something they treat the roses with that probably does inhibit the rooting process. But I know it can be done. There was a lady on the Forums several yrs ago who rooted lots of them. I haven't seen her on here in a long time. Ya know, last night I looked at that video you posted about growing roses from seed. It's funny, I kept watching all sorts of rose propagating videos on YouTube. Some are hilarious. And some are very informative. And some are interesting, but incomplete. They don't show the end results. Anyway, in one of the videos, I saw a rooting product that intrigued me, and I ordered some from Amazon last night. It's called "Clonex gel." It's a super-concentrated rooting hormone that seals the end of the cutting. The reviews sounded great. Most people got well over 90% success. That's of course many other types of plants, but some that were difficult to root otherwise. I can't wait to try it now!

Correcting iron chlorosis is a process that is slower than watching paint dry so expect to have to wait several week for improvements. I normally see leaf improvements starting in close to 2 weeks and the changes happen faster when I use liquids (iron-chelated liquid compounds) instead of granular amendments. Iron chlorosis starts with light green leaves that turn yellow or even white, all the while staying dark green around the leaf veins. But other mineral deficiencies can have similar symptoms. If you notice no improvements after -say- two week or two and a half weeks, there may be another mineral that is low or there may be damage to the roots that produces the chlorosis. After no improvements in that time frame, I would check the roots, get a soil test/analysis done asap and add some fertilizer (which you already added this as compost) with lots of secondary minerals (other than the usual NPK) to see if that helps. Over-watering can also sometimes trigger chlorosis when it rains a lot very quickly in places that do not drain very well. It too goes away slowly. Unclear what the roots issue may be without a few pictures but -just a comment- some hydrangeas develop adventitious roots near the surface. I cannot see what you see but, I usually cover them with mulch and let them be (they will eventually dry out). If some pest however, is injuring the hydrangea roots then you need to cover and protect the roots and take appropriate action to identify and block the pest in your garden. Surprising -in a good way- that the plant is growing and still blooming fine if the roots are disturbed!